Electrodeposited CoP2 on CO2-laser-modified graphite felt: a robust electrocatalyst for nitrite reduction to ammonia

Abstract

The conversion of nitrite-based pollutants to value-added ammonia (NH3) via sustainable electrocatalysis represents a remarkable advancement in waste management research. Herein, a two-step strategy was developed to synthesize well-dispersed cobalt phosphide (CoP2) on graphene oxide (GO)-graphite felt (GF), termed CoP2/GO-GF. The electrodeposited CoP2 exhibited exceptional performance in the electrocatalytic NO2- to NH3 reduction reaction (NO2RR), achieving a maximum NH3 yield rate of 10.6 mg h-1 cm-2 with a faradaic efficiency of 80% at -0.4 V vs. the reversible hydrogen electrode (RHE). The high efficiency of CoP2/GO-GF is attributed to its improved surface-active site density, enhanced electrochemical double-layer capacitance (3.37 mF cm-2), and optimized electron transfer resistance (13.31 Omega). Furthermore, a turnover frequency analysis of the NO2RR indicated the abundance of active sites, facilitating smooth charge tunneling from CoP2 to CO2 laser-developed GO on GF in CoP2/GO-GF. In situ FTIR analysis confirmed the sequential reduction pathway from NO2- to NH3, identifying NO as a key intermediate. Additionally, density functional theory (DFT) calculations revealed a moderate free energy barrier (0.26 eV) for the rate-limiting step, thus validating the thermodynamic feasibility of the reaction. Furthermore, durability tests demonstrated stable performance over 10 reuse cycles, confirming the efficiency and robustness of CoP2/GO-GF as an electrocatalyst in the NO2RR.