Improved Nitrate-to-Ammonia Electrocatalysis through Hydrogen Poisoning Effects

Electrochemical conversion from nitrate to ammonia is a key step in sustainable ammonia production. However, it suffers from low productive efficiency or high energy consumption due to a lack of desired electrocatalysts. Here we report nickel cobalt phosphide (NiCoP) catalysts for nitrate-to-ammonia electrocatalysis that display a record-high catalytic current density of -702±7 mA cm^-2, ammonia production rate of 5415±26 mmol g_cat ^-1 h^-1 and Faraday efficiency of 99.7±0.2 % at -0.3 V vs. RHE, affording the estimated energy consumption as low as 22.7 kWh kg_ammonia ^-1. Theoretical and experimental results reveal that these catalysts benefit from hydrogen poisoning effects, which leave behind catalytically inert adsorbed hydrogen species (H_I*) at Co-hollow sites and thereupon enable ideally reactive H_II* at secondary Co-P sites. The dimerization between H_I* and H_II* for H₂ evolution is blocked due to the catalytic inertia of H_I* thereby the H_II* drives nitrate hydrogenation timely. With these catalysts, the continuous ammonia production is further shown in an electrolyser with a real energy consumption of 18.9 kWh kg_ammonia ^-1.