Enhanced reduction of nitrate by noble metal-free electrocatalysis on P doped three-dimensional Co3O4 cathode: Mechanism exploration from both experimental and DFT studies

Developing green, sustainable and economical materials for emerging electrochemical remediation of nitrate (NO3-) contaminant have attracted immense research interest. In this study, a cost-effective and stable three-dimensional P-doped Co3O4/nickel foam (NF) was prepared for electrocatalytic reduction of NO3- in water. The doping of P could replace the lattice oxygen in Co3O4 and lead to the enhancements in Co3+ percentage and empty d orbitals. As a result, the relative energy for Volmer reaction and the adsorption energy of atomic H* decreased to be -0.73 eV and -3.60 eV, respectively. Furthermore, the higher electrochemical active area and lower interface impedance of Co3O4 were attained after P doping. The P-2.1-Co3O4/NF cathode outperformed Co3O4/NF in the NO3- reduction rate (8.45 times faster) and contribution of atomic H* (2.37 folds increase in the ratio). And almost 100% N-2 selectivity can be obtained in the presence of 2500 mg L-1 chloride ions. Generally, this study provided a new paradigm for designing more practical non-metallic catalyst for NO3- reduction.