Benchmarking photocatalysts for dinitrogen photoreduction reaction

The photocatalytic nitrogen reduction reaction (pNRR) for ammonia (NH₃) production is often discussed as a sustainable alternative to the thermocatalytic Haber-Bosch process. One of the main challenges in pNRR research is the lack of reliable detection of photochemically produced NH₃ since NH₃ concentrations are often low and nitrogen-containing impurities may be present. Here, we identify three key sources of contamination (feed gases, catalyst precursors, and hole scavengers) and systematically quantify and reduce the contamination. We developed a custom photoreactor setup to minimize contamination and benchmarked three photocatalysts previously reported to be active toward pNRR. Our results indicate that the pNRR rates of all three catalysts under benchmarking conditions are much lower than previously reported and in some cases have negligible activity. We suggest essential control experiments to contribute to the standardization of NH₃ measurements in the pNRR field and to help the field elucidate the photoactivity of catalysts toward pNRR.