The authors thank the EPSRC and Intelligent Energy Ltd for funding this project. PB also thanks the SCI for the award of a Messel Scholarship.

1. Set-up of Data-logging Software
<ol>
	<li>Install the data collection and spreadsheet software onto a computer equipped with an RS232 serial port.</li>
	<li>Connect the computer to the balance using an appropriate RS232 connector cable (in this method both the computer and the balance required a 9-pin connector). The balance will typically be connected to COM1.</li>
	<li>Open the data collection software.</li>
	<li>To log the data in a spreadsheet (e.g., Excel), go to &#39;Mode&#39;, then &#39;Send keystrokes to&#39;, enter the appropriate name of the spreadsheet software in the &#39;Application Title Bar Text&#39; and select &#39;excel.exe&#39; in the &#39;Command line&#39;, then press &#39;OK&#39;. A check mark should appear next to &#39;Send Keystrokes To&#39; in the &#39;Mode&#39; drop-down menu.</li>
	<li>Go to &#39;Port&#39;, then &#39;Settings&#39;, and ensure that the values are appropriate to the balance in question, then press &#39;OK&#39;.</li>
	<li>Go to &#39;Define&#39;, then &#39;Define input data record structure&#39;, and select &#39;Numeric char received&#39; in the &#39;Start Of Record Event&#39; section and &#39;Carriage Return or CrLf Received&#39; in the &#39;End Of Record Event&#39; section, then press &#39;Continue&#39;.</li>
	<li>When a box entitled &#39;Input Record Structure&#39; appears, select &#39;Each data record contains a single data field&#39; and then press &#39;Continue&#39;.</li>
	<li>When a box entitled &#39;Input Record Definition Editor - Send Keystrokes Mode&#39; appears: in Field 1, set the &#39;Input Filter&#39; to &#39;Numeric Data Only&#39; and the &#39;Field Postamble Keystrokes&#39; to &#39;{Tab}{Minute}:{Second}{LEFT}{DOWN}&#39; and then press &#39;OK&#39;.</li>
	<li>Go to &#39;Define&#39;, then &#39;Define hot keys and hot actions&#39;. Select Hot Key 1, then select the Hot Key Action &#39;Suspend WinWedge&#39; and assign this the Hot Key Keystroke of &#39;BACKSPACE&#39;, and press OK.</li>
	<li>Go to &#39;File&#39;, then &#39;Save As&#39;, and save the method in an appropriate folder.</li>
</ol>
2. Experimental Set-up
<ol>
	<li>Add water to a glass bowl until it is approximately &#190; full. Then, place the glass bowl on a temperature-controlled stirrer-hotplate and heat to 50 &#176;C; alternatively, use a thermostatically controlled water bath.</li>
	<li>Add deionized water (5 ml) to a 50 ml round-bottomed flask and position this in the water bath such that the level of the water in the bath is well above the level of water in the flask.</li>
	<li>Insert a thermometer into the neck of the round-bottomed flask to monitor the water temperature (after equilibration, the temperature of the water in the flask is usually ~ 5 &#176;C lower than the set point on the hotplate). 
	Note: The set-up is ready when the temperature of the water in the flask remains constant over a 10 min period.</li>
	<li>Fill a beaker with deionized water.</li>
	<li>Place an empty beaker onto the data-logging balance.</li>
	<li>Construct a bridge from plastic sheet which can transfer water from the spout of the beaker to the empty beaker on the data-logging balance. Ensure that the plastic bridge is not in physical contact with the beaker on the data-logging balance.</li>
	<li>Fill a 500 ml measuring cylinder with deionized water.</li>
	<li>While covering the open end with a gloved hand, invert the measuring cylinder and place it into the beaker such that the open end of the measuring cylinder is just below the surface of the water.</li>
	<li>Use a retort stand fitted with two bosses and clamps to support the measuring cylinder. Depending on the size of the measuring cylinder, place counterweights on the base of the retort stand to prevent it from falling due to the weight of the water.</li>
	<li>Adjust the position of the beaker such that the spout is in contact with the plastic bridge.</li>
	<li>Carefully raise the measuring cylinder to allow release of water and ingress of air to ensure that the level of air in the measuring cylinder is consistent at the beginning of each experiment (for example, 100 ml of air).</li>
	<li>Insert the non-ground glass joint end of a modified adapter into a length of tubing. Seal by carefully wrapping Parafilm around the connection between the joint and the tubing.</li>
	<li>Insert the end of the tubing into the measuring cylinder.</li>
	<li>Ensure that the addition of excess water will result in it running off onto the balance by adding some water to the beaker. Leaks can occur at high flow rates at the connection between the beaker&#39;s spout and the plastic bridge.</li>
	<li>Ensure that the balance does not read zero. If necessary, add some water to the beaker on the data-logging balance.</li>
	<li>Using a balance, weigh out either 0.05, 0.10, 0.15, 0.20, or 0.25 g of silicon into a small glass vial; do not use a plastic weighing boat as some silicon tends to be trapped on the inner neck of the flask when it is added to the reaction mixture from a weighing boat. This problem is avoided by instead rapidly inverting a small glass vial into the neck of the flask.</li>
</ol>
3. Experimental Procedure
<ol>
	<li>Add sodium hydroxide solution (5 ml, 20 wt%) to a 50 ml round-bottomed flask and position this in the water bath such that the level of the water in the bath is well above the level of water in the flask.</li>
	<li>Insert a thermometer into the neck of the round-bottomed flask to monitor the solution temperature (after equilibration, the temperature of the water in the flask in this set-up is usually ~ 5 &#176;C lower than the set point on the hotplate).</li>
	<li>Leave for 10 min to equilibrate.</li>
	<li>Before the equilibration period ends, open a new spreadsheet in the spreadsheet software package and then open the data collection software. Load the method created in Step 1 by going to &#39;File&#39; on the data collection software start menu, and then &#39;Open method&#39;.</li>
	<li>Just before the 10 min equilibration period is due to end, go to &#39;Activate&#39; and then click on &#39;Normal mode&#39;. Data will start being logged in the spreadsheet software package.</li>
	<li>At the end of the 10 min equilibration period, add the silicon by rapidly inverting the glass vial and depositing the silicon into the sodium hydroxide solution.</li>
	<li>Rapidly place the ground glass joint of the adapter which is attached to the tubing into the neck of the round bottomed flask. Zero the balance. The moment at which the balance is zeroed will be taken as time (t) = 0 in the data analysis.</li>
	<li>After 10 min have elapsed, stop the data logging by pressing the backspace key and then selecting the &#39;Quit&#39; option on the data collection software menu. Save the file in the spreadsheet software package.</li>
	<li>Remove the adapter which is attached to the tubing from the round-bottomed flask and add water to quench the reaction.</li>
	<li>Isolate the solid residue in the flask for further analysis by centrifugation or gravity filtration, or transfer the entire reaction mixture to a beaker and neutralize with hydrochloric acid (1 M) and dispose of the waste appropriately.</li>
</ol>
4. Data Analysis
<ol>
	<li>Ensure that the data is loaded into an appropriate spreadsheet software package.</li>
	<li>Find the point at which the balance is zeroed; this is considered to be the (t) = 0 point of the reaction.</li>
	<li>Delete the data which precedes this.</li>
	<li>Insert a column to the left of this data. This will contain the time.</li>
	<li>Add appropriate time intervals, starting from zero, to the column which has just been inserted. The balance used in these studies logged 8.5 data points per second, and thus time intervals of 0.117647 (=1/8.5) sec were used.</li>
	<li>Consider gas which has been collected over water to be saturated with water vapor. During the collection process, the water level in the measuring cylinder adjusts to maintain the internal pressure in the measuring cylinder at atmospheric pressure.</li>
	<li>Apply an approximate correction factor using Dalton&#39;s Law, which states that the sum of the individual partial pressures of the gases in a mixture (P1&#8230;Pn) is equal to the total pressure (Ptot). As, if the room temperature is 298 K, the partial pressure of water vapor is 31,69.9 Pa, and the total pressure of gas in the measuring cylinder is atmospheric pressure (101,325 Pa), it can be calculated that there is approximately 3.08% water vapor by volume in the collected gas. Estimate the amount of water vapor in the hydrogen at other temperatures by using the partial pressure of water vapor at the temperature in question.</li>
	<li>To obtain an estimate of the amount of hydrogen generated (if the room temperature is 298 K), multiply the gas volume by 0.97.</li>
	<li>Estimate the initial hydrogen generation rate by fitting a linear trend line to the initial steep slope of the hydrogen generation curve.</li>
	<li>Take the induction period as the time taken for water to be displaced from the measuring cylinder. These estimates of induction period are not absolute; the actual hydrogen generation reaction starts before the end of the &#39;induction period&#39; estimated in these experiments as a certain amount of hydrogen must be generated to be able to begin displacing water. However, these values do allow for an assessment of the relative change in induction period between experiments.</li>
</ol>

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The authors have nothing to disclose.

The most critical steps of the protocol are those which occur at the beginning of an experiment. The large temperature dependence of the rate of these hydrolysis reactions means that great care must be taken to ensure that the solution temperature has reached equilibrium before the addition of the solid. The solid must be added rapidly and completely, the ground glass joint of the adapter must be properly inserted into the neck of the round-bottomed flask, and the balance must then be zeroed as rapidly as possible. An incorrect measurement of start time and reaction temperature will generate incorrect results.
The method does have some limitations. It is imperative that the beaker into which the measuring cylinder is inserted is as narrow as practicable to ensure that the water displaced from the measuring cylinder is rapidly channeled down the plastic bridge onto the balance. Otherwise, the surface tension of the water allows for a slow buildup of the water level at low flow rates (see Figure 5) until the point at which all of the water is released in a large drip.
The error of the balance also limits the resolution of the data. In these experiments, a balance with an error of &#177; 0.05 g was used, which is adequate when generating several hundred milliliters of hydrogen, but a balance with a smaller error would be required if smaller volumes were being measured.
As the displaced water drips from the bridge onto the balance, the mass recorded by the balance oscillates, i.e., as a drip falls onto the balance, the balance momentarily records a slightly larger mass. This means that differentiation of high time resolution raw data using software packages is problematic as the gradient oscillates. The most appropriate way to find the gradient of the steepest part of the hydrogen generation curve, and thus the hydrogen generation rate, is to fit a straight line to it and calculate its gradient.
By automatically logging the data in a spreadsheet, this method offers a significant improvement in accuracy and temporal resolution with respect to water displacement methods which rely on recording the volume of gas evolved manually. However, though it is considerably lower in cost than methods which use cameras and image analysis software to track gas evolution, it is generally lower in temporal resolution, and such camera-based methods also avoid the problem of oscillating mass-balance readings due to water forming drops and therefore produce data which can be more easily processed by differentiation.
The water displacement method is applicable to the collection of any gas that has low solubility in water. Thus, this experimental protocol could be modified for the measurement of rates of gas generation from other chemical reactions which evolve poorly water soluble gases.

Due to their high energy density, lithium-ion batteries are currently one of the most popular power sources for portable consumer electronics. However, the amount of energy that can be delivered by a battery is limited. There is thus currently much interest in developing alternative methods of providing portable power. One of the more promising methods is the use of proton exchange membrane (PEM) fuel cells, which generate electricity and water by combining hydrogen and oxygen. PEM fuel cells have two main advantages over batteries. Firstly, PEM fuel cells can provide power for a much longer period of time (as long as a flow of hydrogen is maintained). Secondly, depending on the fuel source, PEM fuel cells can have a much greater energy density than batteries, meaning that a smaller system can provide more energy.1,2 As a result of this, there is a currently a large amount of research directed at developing portable, on-demand hydrogen sources.2-7 One method which is currently receiving much attention is the generation of hydrogen by reacting chemicals with water.8,9
One of the most important parameters which must be measured in these reactions is the evolution of hydrogen. For simple reactions, such as the evolution of hydrogen by the addition of chemical hydrogen storage materials to aqueous solutions, it is advantageous to have a simple, low cost measurement system. An example of such a system is the water displacement method, in which the volume of gas generated in a chemical reaction is measured simply by tracking the volume of water displaced from an inverted water-filled measuring cylinder. This technique originated in the pneumatic trough, which was developed by the botanist Stephen Hales and then adapted and put to its most famous use by Joseph Priestley to isolate several gases, including oxygen, in the 18th century.10,11 The water displacement method is applicable to any gas which is not particularly soluble in water, including hydrogen, and is still widely used to record the volume of hydrogen generated from the reactions of various chemicals, such as sodium borohydride, aluminum, and ferrosilicon, with water.12-20
However, the classic water displacement method, involving manual recording of the changes in the water level as gas is evolved, is tedious and can, at higher gas flow rates when the water level changes rapidly, be inaccurate, as it is difficult for the experimenter to take an accurate reading. Manually recorded data is also inherently low in temporal resolution, as an experimenter cannot realistically take readings at smaller intervals than ~ 10 sec.
Several researchers have overcome this problem by using cameras to record the water displacement process and data analysis software to extract the change in volume over time.21-25 However, this requires knowledge of computer programming and relatively expensive equipment. Other researchers have made use of mass-flow meters to record the hydrogen flow.26-29 However, these are often only capable of detecting gas over a narrow range, and are better suited to applications in which the flow is maintained at a relatively constant level.
A simpler approach to obtaining higher resolution, more accurate data is to channel the water displaced by hydrogen evolution into a receiver vessel which is placed on a mass balance.30-35 The variation of this method described herein makes use of general laboratory grade glassware and a low-cost, commercially available balance to record hydrogen evolution from the reaction of silicon with aqueous sodium hydroxide solutions. Rather than being manually recorded, the data is logged in a spreadsheet using a data collection software package which allows the balance to send data to the computer. It should be noted that while this technique is appropriate for measuring hydrogen evolution on the milliliter scale, it is not suitable for measuring very small (due to the uncertainty in the balance) or very large (due to the limited size of the measuring cylinder) volumes of hydrogen without appropriate adaptation (i.e., using a higher resolution balance or a larger measuring cylinder).

<table><tbody><tr><td>WinWedge software</td><td>Taltech</td><td></td><td>http://www.taltech.com/winwedge</td></tr><tr><td>High Resolution Top Loader Balance</td><td>LW Measurements, LLC</td><td>HRB6001</td><td>http://www.lwmeasurements.com/HRB-6001-High-Resoultion-Top-Loader-Balance-p/hrb6001.htm</td></tr><tr><td>Silicon</td><td>Sigma Aldrich</td><td>215619</td><td>325 mesh</td></tr><tr><td>Sodium hydroxide</td><td>Sigma Aldrich</td><td>221465</td><td>Reagent grade</td></tr><tr><td>Aluminium (65.7%)-silicon (34.3%) alloy&amp;nbsp;</td><td>Goodfellow</td><td>275-274-74</td><td></td></tr><tr><td>Excel</td><td>Microsoft</td><td></td><td>https://products.office.com/en-us/excel</td></tr><tr><td>Glass sample vials, 50 x 12 mm</td><td>Scientific Laboratory Supplies</td><td>TUB1152</td><td></td></tr><tr><td>Plastic sheet</td><td></td><td></td><td>Recycled from a smooth-sided plastic drinks bottle</td></tr><tr><td>Silicone tubing, 5 x 8 mm BxO D</td><td>Scientific Laboratory Supplies</td><td>TUB3806</td><td></td></tr><tr><td>Parafilm (2 in. by 250 ft.)</td><td>Sigma Aldrich</td><td>P7543</td><td></td></tr><tr><td>Adapter</td><td>Sigma Aldrich</td><td>Z415685</td><td>We used a custom-made adapter in our set-up, but this type of fitting would serve the same function</td></tr></tbody></table>

a simple, low-cost, and robust system to measure the volume of hydrogen evolved by chemical reactions with aqueous solutions

There is a growing research interest in the development of portable systems which can deliver hydrogen on-demand to proton exchange membrane (PEM) hydrogen fuel cells. Researchers seeking to develop such systems require a method of measuring the generated hydrogen. Herein, we describe a simple, low-cost, and robust method to measure the hydrogen generated from the reaction of solids with aqueous solutions. The reactions are conducted in a conventional one-necked round-bottomed flask placed in a temperature controlled water bath. The hydrogen generated from the reaction in the flask is channeled through tubing into a water-filled inverted measuring cylinder. The water displaced from the measuring cylinder by the incoming gas is diverted into a beaker on a balance. The balance is connected to a computer, and the change in the mass reading of the balance over time is recorded using data collection and spreadsheet software programs. The data can then be approximately corrected for water vapor using the method described herein, and parameters such as the total hydrogen yield, the hydrogen generation rate, and the induction period can also be deduced. The size of the measuring cylinder and the resolution of the balance can be changed to adapt the setup to different hydrogen volumes and flow rates.

To investigate the reproducibility of the experimental set-up, varying masses of silicon were reacted with aqueous sodium hydroxide solutions to generate hydrogen. Each reaction was performed in triplicate. The average hydrogen generation curves are shown in Figure 1. Average total hydrogen yields, hydrogen generation rates, and induction periods for each mass of silicon were also calculated and are plotted with error bars representing one standard deviation in Figures 2, 3, and 4, respectively. There was very little deviation in the total hydrogen yields and hydrogen generation rates between reactions, and a greater level of deviation in the induction periods.
<img alt="Figure 1" src="/files/ftp_upload/54383/54383fig1.jpg" /> 
Figure 1: Example of Hydrogen Generation Curves from the Reaction of Silicon with Aqueous Sodium Hydroxide. Various masses of silicon (0.05, 0.10, 0.15, 0.20 and 0.25 g) were reacted with aqueous sodium hydroxide solution (5 ml, 20 wt%) at 50 &#176;C. Hydrogen generation was recorded for a period of 10 min. The reactions were conducted in triplicate and the results averaged. <a href="https://www.jove.com/files/ftp_upload/54383/54383fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/54383/54383fig2.jpg" /> 
Figure 2: Example of Hydrogen Yield Values from the Reaction of Silicon with Aqueous Sodium Hydroxide. The total volumes of hydrogen evolved in 10 min were deduced from the hydrogen generation curves. The average total hydrogen yields for each mass of silicon were obtained and plotted. It can be seen that there is a linear relationship between the mass of silicon used in the reaction and the volume of hydrogen generated under these reaction conditions. The error bars represent one standard deviation of the total hydrogen yields. <a href="https://www.jove.com/files/ftp_upload/54383/54383fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/54383/54383fig3.jpg" /> 
Figure 3: Example of Hydrogen Generation Rate Values from the Reaction of Silicon with Aqueous Sodium Hydroxide. The initial or maximum rates of hydrogen generation for each mass of silicon were calculated from the hydrogen generation curves. The average initial or maximum hydrogen generation rates for each mass of silicon were obtained and plotted. It can be seen that, on average, there is a power relationship between the mass of silicon used in the reaction and the initial or maximum hydrogen generation rate observed under these reaction conditions. The error bars represent one standard deviation of the initial or maximum hydrogen generation rates. <a href="https://www.jove.com/files/ftp_upload/54383/54383fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/54383/54383fig4.jpg" /> 
Figure 4: Example of Induction Period Values from the Reaction of Silicon with Aqueous Sodium Hydroxide. The induction periods for the hydrogen generation for each mass of silicon were deduced from the hydrogen generation curves. The average induction period for each mass of silicon was obtained and plotted. It can be seen that, on average, there is no great change in the induction period between the experiments. The error bars represent one standard deviation of the initial or maximum hydrogen generation rates. <a href="https://www.jove.com/files/ftp_upload/54383/54383fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Figure 5 shows some representative results from a sub-optimal experiment. In this case, the low flow of hydrogen between 200 and 800 sec results in the build-up of drips due to the surface tension of the water, which fell at approximately 400 and 710 sec. Though these drips do not affect the calculation of the maximum hydrogen generation rate, they could have an effect on the total hydrogen yield if, for example, the measurement was stopped before the drip fell. It is thus necessary to either alter the reaction conditions (in this case, for example, by adding a greater mass of aluminum-silicon alloy or using a higher concentration of sodium hydroxide) to ensure a higher flow of gas or the reaction setup to prevent the buildup of drips.
<img alt="Figure 5" src="/files/ftp_upload/54383/54383fig5.jpg" /> 
Figure 5: Example of a Sub-optimal Experiment. In this experiment, aluminum (65.7%)-silicon (34.3%) alloy (0.2 g) was reacted with aqueous sodium hydroxide solution (5 ml, 10 wt%) at 40 &#176;C. Though at the initial high rates of hydrogen evolution the recording of the hydrogen generation is optimal, as the flow slows the surface tension of the water results in drips being formed. The drips fall at approximately 400 and 710 sec, in this case. <a href="https://www.jove.com/files/ftp_upload/54383/54383fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions at JoVE.com

A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions

The study of methods to generate on-demand hydrogen for fuel cells continues to grow in importance. However, systems to measure hydrogen evolution from the reaction of chemicals with water can be complicated and expensive. This article details a simple, low-cost, and robust method to measure the evolution of hydrogen gas.

There is a growing research interest in the development of portable systems which can deliver hydrogen on-demand to proton exchange membrane (PEM) ...

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19.5K Views.  Loughborough University. The study of methods to generate on-demand hydrogen for fuel cells continues to grow in importance. However, systems to measure hydrogen evolution from the reaction of chemicals with water can be complicated and expensive. This article details a simple, low-cost, and robust method to measure the evolution of hydrogen gas.

Video: A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions

High-pressure Sapphire Cell for Phase Equilibria Measurements of CO2/Organic/Water Systems

The high pressure sapphire cell apparatus was constructed to visually determine the composition of multiphase systems without physical sampling. Specifically, the sapphire cell enables visual data collection from multiple loadings to solve a set of material balances to precisely determine phase composition. Ternary phase diagrams can then be established to determine the proportion of each component in each phase at a given condition. In principle, any ternary system can be studied although ternary systems (gas-liquid-liquid) are the specific examples discussed herein. For instance, the ternary THF-Water-CO2 system was studied at 25 and 40&#160;&#176;C and is described herein. Of key importance, this technique does not require sampling. Circumventing the possible disturbance of the system equilibrium upon sampling, inherent measurement errors, and technical difficulties of physically sampling under pressure is a significant benefit of this technique. Perhaps as important, the sapphire cell also enables the direct visual observation of the phase behavior. In fact, as the CO2 pressure is increased, the homogeneous THF-Water solution phase splits at about 2 MPa. With this technique, it was possible to easily and clearly observe the cloud point and determine the composition of the newly formed phases as a function of pressure.
The data acquired with the sapphire cell technique can be used for many applications. In our case, we measured swelling and composition for tunable solvents, like gas-expanded liquids, gas-expanded ionic liquids and Organic Aqueous Tunable Systems (OATS)1-4. For the latest system, OATS, the high-pressure sapphire cell enabled the study of (1) phase behavior as a function of pressure and temperature, (2) composition of each phase (gas-liquid-liquid) as a function of pressure and temperature and (3) catalyst partitioning in the two liquid phases as a function of pressure and composition. Finally, the sapphire cell is an especially effective tool to gather accurate and reproducible measurements in a timely fashion.

High-pressure Sapphire Cell for Phase Equilibria Measurements of CO2/Organic/Water Systems

The high pressure sapphire cell apparatus is a unique tool to study, without sampling, phase behavior under a wide range of pressures. Using a cathetometer, very precise volume measurements can be recorded to measure liquid expansion and phase composition. Thus, this synthetic method enables the study of (1) phase equilibria of multi-component mixtures and (2) the partition behavior of catalyst or model compounds as a function of pressure.

The high pressure sapphire cell apparatus was constructed to visually determine the composition of multiphase systems without physical sampling. ...

Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase

Understanding the chemistry of redox proteins demands methods that provide precise control over redox centers within the protein. The technique of protein film electrochemistry, in which a protein is immobilized on an electrode surface such that the electrode replaces physiological electron donors or acceptors, has provided functional insight into the redox reactions of a range of different proteins. Full chemical understanding requires electrochemical control to be combined with other techniques that can add additional structural and mechanistic insight. Here we demonstrate a technique, protein film infrared electrochemistry, which combines protein film electrochemistry with infrared spectroscopic sampling of redox proteins. The technique uses a multiple-reflection attenuated total reflectance geometry to probe a redox protein immobilized on a high surface area carbon black electrode. Incorporation of this electrode into a flow cell allows solution pH or solute concentrations to be changed during measurements. This is particularly powerful in addressing redox enzymes, where rapid catalytic turnover can be sustained and controlled at the electrode allowing spectroscopic observation of long-lived intermediate species in the catalytic mechanism. We demonstrate the technique with experiments on E. coli hydrogenase 1 under turnover (H2 oxidation) and non-turnover conditions.

Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase

Here, we describe a technique, protein film infrared electrochemistry, which allows immobilized redox proteins to be studied spectroscopically under direct electrochemical control at a carbon electrode. Infrared spectra of a single protein sample can be recorded at a range of applied potentials and under a variety of solution conditions.

Understanding the chemistry of redox proteins demands methods that provide precise control over redox centers within the protein. The technique of protein ...

Biochemistry

Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and non-destructively reveals the hydrogen density distribution at surfaces, at interfaces, and in the volume of solid materials with high depth resolution. The technique applies a 15N ion beam of 6.385 MeV provided by an electrostatic accelerator and specifically detects the 1H isotope in depths up to about 2 &#956;m from the target surface. Surface H coverages are measured with a sensitivity in the order of ~1013 cm-2 (~1% of a typical atomic monolayer density) and H volume concentrations with a detection limit of ~1018 cm-3 (~100 at. ppm). The near-surface depth resolution is 2-5 nm for surface-normal 15N ion incidence onto the target and can be enhanced to values below 1 nm for very flat targets by adopting a surface-grazing incidence geometry. The method is versatile and readily applied to any high vacuum compatible homogeneous material with a smooth surface (no pores). Electrically conductive targets usually tolerate the ion beam irradiation with negligible degradation. Hydrogen quantitation and correct depth analysis require knowledge of the elementary composition (besides hydrogen) and mass density of the target material. Especially in combination with ultra-high vacuum methods for in-situ target preparation and characterization, 1H(15N,&#945;&#947;)12C NRA is ideally suited for hydrogen analysis at atomically controlled surfaces and nanostructured interfaces. We exemplarily demonstrate here the application of 15N NRA at the MALT Tandem accelerator facility of the University of Tokyo to (1) quantitatively measure the surface coverage and the bulk concentration of hydrogen in the near-surface region of a H2 exposed Pd(110) single crystal, and (2) to determine the depth location and layer density of hydrogen near the interfaces of thin SiO2 films on Si(100).

We illustrate the application of 1H(15N,&#945;&#947;)12C resonant nuclear reaction analysis (NRA) to quantitatively evaluate the density of hydrogen atoms on the surface, in the volume, and at an interfacial layer of solid materials. The near-surface hydrogen depth profiling of a Pd(110) single crystal and of SiO2/Si(100) stacks is described.

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and ...

Engineering

Measurement of Outgassing Rates of Steels

Steels are commonly used materials in the fabrication of vacuum systems because of their good mechanical, corrosion, and vacuum properties. A variety of steels meet the criterion of low outgassing required for high or ultrahigh vacuum applications. However, a given material can present different outgassing rates depending on its manufacturing process or the various pretreatment processes involved during the fabrication. Thus, the measurement of outgassing rates is highly desirable for a specific vacuum application. For this reason, the rate-of-pressure rise (RoR) method is often used to measure the outgassing of hydrogen after bakeout. In this article, a detailed description of the design and execution of the experimental protocol involved in the RoR method is provided. The RoR method uses a spinning rotor gauge to minimize errors that stem from outgassing or the pumping action of a vacuum gauge. The outgassing rates of two ordinary steels (stainless steel and mild steel) were measured. The measurements were made before and after the heat pretreatment of the steels. The heat pretreatment of steels was performed to reduce the outgassing. Extremely low rates of outgassing (on the order of 10&#8722;11 Pa m3 sec&#8722;1 m&#8722;2) can be routinely measured using relatively small samples.

A protocol for the measurement of outgassing rates of hydrogen from ordinary steel vacuum chambers using the rate-of-pressure rise method is presented.

Steels are commonly used materials in the fabrication of vacuum systems because of their good mechanical, corrosion, and vacuum properties. A variety of ...

Quantitative Analysis by Thermogravimetry-Mass Spectrum Analysis for Reactions with Evolved Gases

During energy conversion, material production, and metallurgy processes, reactions often have the features of unsteadiness, multistep, and multi-intermediates. Thermogravimetry-mass spectrum (TG-MS) is seen as a powerful tool to study reaction features. However, reaction details and reaction mechanics have not been effectively obtained directly from the ion current of TG-MS. Here, we provide a method of an equivalent characteristic spectrum analysis (ECSA) for analyzing the mass spectrum and giving the mass flow rate of reaction gases as precise as possible. The ECSA can effectively separate overlapping ion peaks and then eliminate the mass discrimination and temperature-dependent effect. Two example experiments are presented: (1) the decomposition of CaCO3 with evolved gas of CO2 and the decomposition of hydromagnesite with evolved gas of CO2 and H2O, to evaluate the ECSA on single-component system measurement and (2) the thermal pyrolysis of Zhundong coal with evolved gases of inorganic gases CO, H2, and CO2, and organic gases C2H4, C2H6, C3H8, C6H14, etc., to evaluate the ECSA on multi-component system measurement. Based on the successful calibration of the characteristic spectrum and relative sensitivity of specific gas and the ECSA on mass spectrum, we demonstrate that the ECSA accurately gives the mass flow rates of each evolved gas, including organic or inorganic gases, for not only single but multi-component reactions, which cannot be implemented by the traditional measurements.

Precise determination of the evolved gases&#39; flow rate is key to study the details of reactions. We provide a novel quantitative analysis method of equivalent characteristic spectrum analysis for thermogravimetry-mass spectrum analysis by establishing the calibration system of the characteristic spectrum and relative sensitivity, for obtaining the flow rate.

During energy conversion, material production, and metallurgy processes, reactions often have the features of unsteadiness, multistep, and ...

A Practical and Low-Cost Setup to Measure Methane in Aqueous Samples

Measuring Dissolved Methane in Aquatic Ecosystems Using An Optical Spectroscopy Gas Analyzer

Measuring greenhouse gas (GHG) fluxes and pools in ecosystems are becoming increasingly common in ecological studies due to their relevance to climate change. With it, the need for analytical platforms adaptable to measuring different pools and fluxes within research groups also grows. This study aims to develop a procedure to use portable optical spectroscopy-based gas analyzers, originally designed and marketed for gas flux measurements, to measure GHG concentrations in aqueous samples. The protocol involves the traditional headspace equilibration technique followed by the injection of a headspace gas subsample into a chamber connected through a closed loop to the inlet and outlet ports of the gas analyzer. The chamber is fabricated from a generic mason jar and simple laboratory supplies, and it is an ideal solution for samples that may require pre-injection dilution. Methane concentrations measured with the chamber are tightly correlated (r2 &#62; 0.98) with concentrations determined separately through gas chromatography-flame ionization detection (GC-FID) on subsamples from the same vials. The procedure is particularly relevant for field studies in remote areas where chromatography equipment and supplies are not readily available, offering a practical, cheaper, and more efficient solution for measuring methane and other dissolved greenhouse gas concentrations in aquatic systems.

This study demonstrates an approach to measure methane gas concentrations in aqueous samples using portable optical analyzers coupled to an injection chamber in a closed loop. The results are similar to conventional gas chromatography, presenting a practical and low-cost alternative particularly suitable for remote field studies.

Measuring greenhouse gas (GHG) fluxes and pools in ecosystems are becoming increasingly common in ecological studies due to their relevance to climate ...

Environment

Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions

Developing photocatalytic H2 production devices is the one of the key steps for constructing a global H2-based renewable energy infrastructure. A number of photoactive assemblies have emerged where a photosensitizer and cobaloxime-based H2 production catalysts work in tandem to convert light energy into the H-H chemical bonds. However, the long-term instability of these assemblies and the need for hazardous proton sources have limited their usage. Here, in this work, we have integrated a stilbene-based organic dye into the periphery of a cobaloxime core via a distinct axial pyridine linkage. This strategy allowed us to develop a photosensitizer-catalyst hybrid structure with the same molecular framework. In this article, we have explained the detailed procedure of the synthesis of this hybrid molecule in addition to its comprehensive chemical characterization. The structural and optical studies have exhibited an intense electronic interaction between the cobaloxime core and the organic photosensitizer. The cobaloxime was active for H2 production even in the presence of water as the proton source. Here, we have developed a simple airtight system connected with an online H2 detector for the investigation of the photocatalytic activity by this hybrid complex. This photosensitizer-catalyst dyad present in the experimental setup continuously produced H2 once it was exposed in the natural sunlight. This photocatalytic H2 production by the hybrid complex was observed in aqueous/organic mixture media in the presence of a sacrificial electron donor under complete aerobic conditions. Thus, this photocatalysis measurement system along with the photosensitizer-catalyst dyad provide valuable insight for the development of next generation photocatalytic H2 production devices.

Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions

We have directly incorporated a stilbene-based organic dye into a cobaloxime core to generate a photosensitizer-catalyst dyad for photocatalytic H2 production. We have also developed a simple experimental setup for evaluating the light-driven H2 production by photocatalytic assemblies.

Developing photocatalytic H2 production devices is the one of the key steps for constructing a global H2-based renewable energy infrastructure. A number ...

Hydrogen Production and Utilization in a Membrane Reactor

Industrial hydrogenation consumes ~11 Mt of fossil-derived H2 gas yearly. Our group invented a membrane reactor to bypass the need to use H2 gas for hydrogenation chemistry. The membrane reactor sources hydrogen from water and drives reactions using renewable electricity. In this reactor, a thin piece of Pd separates an electrochemical hydrogen production compartment from a chemical hydrogenation compartment. The Pd in the membrane reactor acts as (i) a hydrogen-selective membrane, (ii) a cathode, and (iii) a catalyst for hydrogenation. Herein, we report the use of atmospheric mass spectrometry (atm-MS) and gas chromatography mass spectrometry (GC-MS) to demonstrate that an applied electrochemical bias across a Pd membrane enables efficient hydrogenation without direct H2 input in a membrane reactor. With atm-MS, we measured a hydrogen permeation of 73%, which enabled the hydrogenation of propiophenone to propylbenzene with 100% selectivity, as measured by GC-MS. In contrast to conventional electrochemical hydrogenation, which is limited to low concentrations of starting material dissolved in a protic electrolyte, the physical separation of hydrogen production from utilization in the membrane reactor enables hydrogenation in any solvent or at any concentration. The use of high concentrations and a wide range of solvents is particularly important for reactor scalability and future commercialization.

Membrane reactors enable hydrogenation in ambient conditions without direct H2 input. We can track the hydrogen production and utilization in these systems using atmospheric mass spectrometry (atm-MS) and gas chromatography mass spectrometry (GC-MS).

Industrial hydrogenation consumes ~11 Mt of fossil-derived H2 gas yearly. Our group invented a membrane reactor to bypass the need to use H2 gas for ...

Vapor-liquid Equilibrium

Source: Michael G. Benton and <a href="https://www.jove.com/author/Kerry+M._Dooley">Kerry M. Dooley</a>, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA
Vapor-liquid equilibrium is paramount in engineering applications such as distillation, environmental modeling, and general process design. Understanding the interactions of components in a mixture is very important in designing, operating and analyzing such separators. The activity coefficient is an excellent tool for relating molecular interactions to mixture composition. Finding the molecular interaction parameters allows future prediction of the activity coefficients for a mixture using a model.
Vapor-liquid equilibrium is a critical factor in common processes in the chemical industry, such as distillation. Distillation is the process of separating liquids by their boiling point. A liquid mixture is fed into a distillation unit or column, then boiled. Vapor-liquid equilibrium data is useful for determining how liquid mixtures will separate. Because the liquids have different boiling points, one liquid will boil into a vapor and rise in the column, while the other will stay as a liquid and drain through the unit. The process is very important in a variety of industries.
In this experiment, the activity coefficients of mixtures of various compositions of methanol, isopropanol, and deionized water will be obtained using a vapor-liquid equilibrium apparatus and gas chromatograph. Additionally, the binary interaction parameters of the system will be determined using Wilson&#39;s equation and the activity coefficients.

Vapor-liquid Equilibrium, Activity Coefficient, Fugacity

Source: Michael G. Benton and Kerry M. Dooley, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA
Vapor-liquid equilibrium is ...

Education

JoVE Science Education

Chemical Engineering

Introduction to Titration

Source: Laboratory of Dr. Yee Nee Tan &#8212; Agency for Science, Technology, and Research
Titration is a common technique used to quantitatively determine the unknown concentration of an identified analyte.1-4 It is also called volumetric analysis, as the measurement of volumes is critical in titration. There are many types of titrations based on the types of reactions they exploit. The most common types are acid-base titrations and redox titrations.5-11
In a typical titration process, a standard solution of titrant in a burette is gradually applied to react with an analyte with an unknown concentration in an Erlenmeyer flask. For acid-base titration, a pH indicator is usually added in the analyte solution to indicate the endpoint of titration.12 Instead of adding pH indicators, pH can also be monitored using a pH meter during a titration process and the endpoint is determined graphically from a pH titration curve. The volume of titrant recorded at the endpoint can be used to calculate the concentration of the analyte based on the reaction stoichiometry.
For the acid-base titration presented in this video, the titrant is a standardized sodium hydroxide solution and the analyte is domestic vinegar. Vinegar is an acidic liquid that is frequently used as a culinary condiment or flavorings. Vinegar mainly consists of acetic acid (CH3COOH) and water. The acetic acid content of commercial vinegar can vary widely and the goal of this experiment is to determine the acetic acid content of commercial vinegar by titration.

A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions

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