Quantification of Hydrogen and Oxygen Production to Assess Selectivity of Electrocatalysts for Solar Water Splitting

Photoelectrochemical water splitting presents an environmentally friendly means of producing hydrogen for use as fuel or industrial feedstock; current research in this field primarily focuses on developing the ideal catalysts and semiconductors for this process. It is undesirable for a given electrocatalyst/semiconductor pair to have less than 100% faradaic efficiency for the solar water splitting reaction, which literature has shown may occur through unwanted side reactions or catalyst/semiconductor degradation. A technique is developed to quantify the production of hydrogen and oxygen in a photoelectrochemical cell in order to assess the faradaic efficiency of electrocatalysts and semiconductor absorbers used for solar water splitting. The process involves commercial hydrogen and oxygen microsensor probes and a custom photoelectrochemical cell optimized for accurate product quantification. The airtight cell consists of two identical compartments separated by an ion exchange membrane and is equipped with ports for all necessary electrodes, product detection sensors, a gas purge, and a thermocouple. Three-point calibrations are performed prior to experimentation using an inert gas purge and then injecting known volumes of hydrogen or oxygen into the cell. The technique’s accuracy is confirmed by ensuring measurements of approximately 100% faradaic efficiency for platinum and iridium electrodes for the hydrogen evolution reaction and oxygen evolution reaction, respectively (a baseline based on previous studies from the literature). The accuracy of hydrogen measurements is further confirmed using gas chromatography. Initial applications include assessing crystalline molybdenum disulfide catalysts on n⁺ silicon wafer cathodes, which are measured to have a faradaic efficiency of 98.6%. Future work will initially focus on improving the technique’s precision and determining the effect of changing temperature on the sensors’ accuracy, after which additional catalysts and semiconductors will be evaluated, including tantalum nitride and strontium titanate photoanodes.