The overall goal of this method is to provide a simple, easy setup for measuring the evolution of hydrogen gas from a chemical reaction. This method can help researchers in the field of hydrogen generation to measure the efficiency of specific catalysts of materials in generating hydrogen from reactions with aqueous solutions. The main advantages of this technique are that it is simple, low-cost, and robust.
Before beginning the procedure, add water to a glass bowl until it is approximately 3/4 full. Then, place the bowl on a temperature-controlled stirrer hotplate set to 50 degrees Celsius. When the water reaches 50 degrees Celsius, place a 50-milliliter round-bottom flask containing five milliliters of de-ionized water into the bowl such that the level of the water in the bowl is well above the level of the water in the flask.
Set a thermometer into the neck of the flask to monitor the temperature. After equilibration, the temperature of the water in the flask is usually approximately five degrees Celsius lower than the set point on the hotplate. When the temperature of the water in the flask remains constant over a 10-minute period, fill a beaker with de-ionized water and place an empty beaker onto a data-logging balance.
Next, use a plastic sheet to construct a bridge for transferring water from the spout of the water beaker to the empty beaker on the data-logging balance, taking care that the plastic bridge is not in physical contact with the beaker on the data-logging balance. When the bridge is in place, fill a 500-milliliter measuring cylinder with de-ionized water and cover the opening of the cylinder with a gloved hand. Invert the cylinder and place it into the beaker of water, such that the opening of the measuring cylinder is just below the surface of the water.
Then, clamp the cylinder to a retort stand fitted with two bosses to hold the cylinder in place. Adjust the position of the beaker such that the spout is in contact with the plastic bridge. Then, carefully raise the measuring cylinder to allow a release of water and in ingress of air to keep the level of the air in the measuring cylinder consistent at the beginning of each experiment.
Insert the non-ground glass joint end of a modified adapter into a length of tubing and carefully wrap parafilm around the connection between the joint and the tubing. Insert the end of the tubing into the measuring cylinder and add water to the beaker to make sure that the excess water runs off onto the balance. Confirm that the data-logging balance does not read zero.
Then, use a separate balance to weight out the appropriate amount of silicon into a small glass vial. Now, place a 50-milliliter round-bottom flask containing 5 milliliters of sodium hydroxide solution into the water bath, such that the level of the water in the bath is well above the level of sodium hydroxide in the flask. Place a thermometer into the neck of the flask and allow the solution to equilibrate for 10 minutes.
During the equilibration, open a new spreadsheet in the appropriate spreadsheet software package and open the data collection software. Load the appropriate data-logging software file. Then, just before the end of the 10 minutes, select Activate and click on Normal Mode to begin logging the data in the spreadsheet software package.
At the end of the 10-minute equilibration period, rapidly invert the glass vial and deposit the silicon directly into the sodium hydroxide solution. Quickly place the ground-glass joint of the adapter into the neck of the round-bottom flask and zero the balance. After 10 minutes, press the backspace key to stop the data logging and select Quit.
Save the file in the spreadsheet software package. Remove the adapter from the round-bottom flask and add water to quench the reaction. The solid residue in the flask can then be isolated for further analysis.
To investigate the reproducability of the experimental setup, varying masses of silicon are reacted with aqueous sodium hydroxide solutions to generate hydrogen. In these representative experiments, there was very little deviation in the total hydrogen yields, and the hydrogen generation rates between the reactions, with a greater level of deviation observed within the periods of induction. In this representative sub-optimal experiment, the low flow of hydrogen between 200 and 800 seconds resulted in a buildup of drips due to the surface tension of the water at approximately 400 and 710 seconds.
Though 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 the measurement was stopped before the drips fell. Once mastered, a hydrogen measurement can be conducted in 30 minutes if the technique is performed properly and the material are catalysts to sufficiently reactive. While attempting this procedure, it's important to remember that it will not work for very rapid or very slow flows of gas.
For our next procedure, the residual material can be isolated, and other methods, like X-Ray Diffraction, infrared spectroscopy, and X-Ray photoelectron spectroscopy, can be performed to investigate the mechanism of hydrogen generation from the materials used. After watching this video, you should have a good understanding of how to measure the hydrogen evolution from the reactions of materials with aqueous solutions using a data-logging balance. Don't forget that working with hydrogen can be hazardous, and that precautions, such as always performing the procedure in a fume hood, should be taken.
