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.

Electrostatic Secondary-Sphere Interactions That Facilitate Rapid and Selective Electrocatalytic CO2 Reduction in a Fe-Porphyrin-Based Metal-Organic Framework.

Metal-organic frameworks (MOFs) are promising platforms for heterogeneous tethering of molecular CO2 reduction electrocatalysts. Yet, to further understand electrocatalytic MOF systems, one also needs to consider their capability to fine-tune the immediate chemical environment of the active site, and thus affect its overall catalytic operation. Here, we show that electrostatic secondary-sphere functionalities enable substantial improvement of CO2 -to-CO conversion activity and selectivity. In situ Raman analysis reveal that immobilization of pendent positively-charged groups adjacent to MOF-residing Fe-porphyrin catalysts, stabilize weakly-bound CO intermediates, allowing their rapid release as catalytic products. Also, by varying the electrolyte's ionic strength, systematic regulation of electrostatic field magnitude was achieved, resulting in essentially 100 % CO selectivity. Thus, this concept provides a sensitive molecular-handle that adjust heterogeneous electrocatalysis on demand.