Dinitrogen Reduction Coupled with Methanol Oxidation for Low Overpotential Electrochemical NH3 Synthesis Over Cobalt Pyrophosphate as Bifunctional Catalyst.

Abstract

Electrochemical dinitrogen (N2 ) reduction to ammonia (NH3 ) coupled with methanol electro-oxidation is presented in the current work. Here, methanol oxidation reaction (MOR) is proposed as an alternative anode reaction to oxygen evolution reaction (OER) to accomplish electrons-induced reduction of N2 to NH3 at cathode and oxidation of methanol at anode in alkaline media thereby reducing the overall cell voltage for ammonia production. Cobalt pyrophosphate micro-flowers assembled by nanosheets are synthesized via a surfactant-assisted sonochemical approach. By virtue of structural and morphological advantages, the maximum Faradaic efficiency of 43.37% and NH3 yield rate of 159.6µg h-1 mgca -1 is achieved at a potential of -0.2V versus RHE. The proposed catalyst is shown to also exhibit a very high activity (100mA mg-1 at 1.48V), durability (2h) and production of value-added formic acid at anode (2.78µmol h-1 mgcat -1 and F.E. of 59.2%). The overall NH3 synthesis is achieved at a reduced cell voltage of 1.6V (200mV less than NRR-OER coupled NH3 synthesis) when OER at anode is replaced with MOR and a high NH3 yield rate of 95.2µg h-1 mgcat -1 and HCOOH formation rate of 2.53µmol h-1 mg-1 are witnessed under full-cell conditions.