Screening of transition metal oxides for electrocatalytic nitrate reduction to ammonia at large currents

Electrochemical nitrate reduction reaction (NO3RR) towards ammonia, as an emerging and appealing technology alternative to the energy-intensive Haber–Bosch process and inefficient nitrogen reduction reaction, has recently aroused wide concern and research. However, the current research of the NO3RR towards ammonia lacks the overall performance comparison of various electrocatalysts. Given this, we here make a comparison of 12 common transition metal oxide catalysts for the NO3RR under a high cathodic current density of 0.25 A·cm−2, wherein Co3O4 catalyst displays the highest ammonia Faradaic efficiency (85.15%) and moderate activity (ca. −0.25 V vs. reversible hydrogen electrode). Other external factors, such as nitrate concentrations in the electrolyte and applied potential ranges, have also been specifically investigated for the NO3RR.