Insights on Measuring and Reporting Heterogeneous Photocatalysis: Efficiency Definitions and Setup Examples

Heterogeneous photocatalysis is a potentially competitive solution for the direct production of solar fuels. This research field has seen tremendous growth over the last five decades, and with such an exciting research topic, it has seen—and will continue to see—an increasing number of papers being published in a variety of journals. However, it is becoming increasingly difficult to compare the efficiencies of heterogeneous photocatalyst powders, because different researchers report their results in different ways. Efforts have been made to create standards for reporting data in this field, but there continues to be a discrepancy in published works. This article intends to clarify efficiency definitions, and clarify misconceptions as to why researchers should avoid reporting rates of evolution per gram, per surface area of catalyst, or as turnover frequencies (TOFs) alone, to be able to compare photocatalytic efficiency among different materials. By providing an example of a photoreactor for water splitting in the authors' laboratory, the paper also intends to guide new researchers in the field. This article does not discuss how to improve photocatalysis but rather how to improve the reporting of photocatalysis to ensure reproducibility and effective benchmarking. Researchers should not only ensure that they have all the appropriate characterization and statistical data to support their claims but should also recognize that improperly reported data may lead to faulty benchmarking that prevents their results from being compared with those of other photocatalysts, inhibiting the progress of photocatalytic research.