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 159.6 µg h−1 mgca−1 is achieved at a potential of −0.2 V versus RHE. The proposed catalyst is shown to also exhibit a very high activity (100 mA mg−1 at 1.48 V), durability (2 h) and production of value‐added formic acid at anode (2.78 µmol h−1 mgcat−1 and F.E. of 59.2%). The overall NH3 synthesis is achieved at a reduced cell voltage of 1.6 V (200 mV less than NRR‐OER coupled NH3 synthesis) when OER at anode is replaced with MOR and a high NH3 yield rate of 95.2 µg h−1 mgcat−1 and HCOOH formation rate of 2.53 µmol h−1 mg−1 are witnessed under full‐cell conditions.

Operando scanning electrochemical microscopic investigation and visualization of NRR-HER competition in electrochemical NH3 synthesis

“…When the origin of NH 3 produced during the NRR was efficaciously tracked, and the validation of the same was implemented by carrying out 15 N 2 -isotope labelling experiments and quantification of produced 14 NH 4 + and 15 NH 4 + yield rates by different methods including spectrophotometry as well as NMR. 45 The electrolyte samples were collected after 2 h of isotope labelling NRR experiments and utilised for ammonia quantification. Prior to the quantification of unknown samples, the standard calibration curves were extracted for known concentrations of NH 4 + via NMR also (Fig.…”

Boosting nucleophilic attack to realize high current density biomass valorization on a tunable Prussian blue analogue

“…† The NiFe-PBA catalyst shows a high catalytic performance in terms of activity (500 mA cm −2 ) and faradaic efficiency (95.8%) toward formate. 9,29,30,[36][37][38][39][40][41][42][43][44] Compared with the catalysts reported, NiFe-PBA/NF can achieve the highest current density while maintaining the FEs of formic acid close to 100%.…”

A perspective on the future of electrochemical ammonia synthesis: aqueous or non-aqueous?

“…Inspired from this, few articles are available in the literature showing effectual HER suppression by the use of alkaline electrolytes and designing a durable electrocatalyst for aqueous ENRR. In a recent report by Gupta et al , 66 a bifunctional CoPPi catalyst has been developed for ENRR in alkaline 0.1 M KOH electrolyte to achieve a high FE of 43.42% at −0.2 V ( vs. RHE) marking itself as one of the best reports so far in ENRR under aqueous alkaline conditions (Fig. 2b).…”