Efficient electrochemical NO reduction to NH3 over metal-free g-C3N4 nanosheets and the role of interface microenvironment

The ever-increasing NO emission has caused severe environmental issues and adverse effects on human health. Electrocatalytic reduction is regarded as a win-win technology for NO treatment with value-added NH3 generation, but the process is mainly relied on the metal-containing electrocatalysts. Here, we developed metal-free g-C3N4 nanosheets (deposited on carbon paper, named as CNNS/CP) for NH3 synthesis from electrochemical NO reduction under ambient condition. The CNNS/CP electrode afforded excellent NH3 yield rate of 15.1 μmol h−1 cm−2 (2180.1 mg gcat−1 h−1) and Faradic efficiency (FE) of ∼41.5 % at − 0.8 and − 0.6 VRHE, respectively, which were superior to the block g-C3N4 particles and comparable to the most of metal-containing catalysts. Moreover, through adjusting the interface microenvironment of CNNS/CP electrode by hydrophobic treatment, the abundant gas-liquid-solid triphasic interface improved NO mass transfer and availability, which enhanced NH3 production and FE to about 30.7 μmol h−1 cm−2 (4424.2 mg gcat−1 h−1) and 45.6 % at potential of − 0.8 VRHE. This study opens a novel pathway to develop efficient metal-free electrocatalysts for NO electroreduction and highlights the importance of electrode interface microenvironment in electrocatalysis.