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

Abstract

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.

Understanding metal–organic frameworks for photocatalytic solar fuel production

“…Accordingly, matching reactant conversion times with the lifetime of photogenerated charges is the key for minimizing charge recombination and maximizing the energy utilized for the photochemical reaction. We believe that the combination of innovative spectroscopic techniques and the appropriate photocatalytic testing 82 will advance this field greatly. Even when achieving a high quantum yield is the ultimate goal, the future growth of MOF-based photocatalysts requires deeper understanding of the operation of current systems and their advantages over other photocatalytic materials.…”

Hydrogen Generation through Solar Photocatalytic Processes: A Review of the Configuration and the Properties of Effective Metal-Based Semiconductor Nanomaterials

“…An effective and low-cost substitute for noble metals is represented by a selected group of Earth-abundant metals including cobalt [119], nickel [120] and copper. In particular, remarkable photoefficiencies were achieved over copper-based metal oxides tested for photocatalytic reforming of several sacrificial organic species [18,121] and in the presence of aqueous matrix with excess chloride ion [122] and nitrate ion [123].…”

“…The efficiency for hydrogen generation through photocatalytic water splitting can be expressed as [17,18]:…”

“…The efficiency for hydrogen generation through photocatalytic water splitting can be expressed as [17,18] 2 ) and S (cm 2 ) are the hydrogen production rate, the standard Gibbs free energy needed to produce one mole of hydrogen from water (237 kJ/mol), the specific power of the light source and the irradiated area, respectively.…”

Photocatalytic Activity: Experimental Features to Report in Heterogeneous Photocatalysis

“…The produced new catalysts are often tested against a specific reaction such as the degradation kinetics of a dye, resulting in works that claim to have improved the photocatalytic efficiency (or enhanced the activity) of the process relative to previous materials, modified stoichiometric ratios, variable geometries, or single components integrated into nanocomposite heterostructures [11,12]. However, such measurements are insufficient to report photocatalytic activities because they lack a mechanism to account for the number of photons driving the process [13,14]. …”