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 Ω). 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.