Synergistic Integration of Amorphous Cobalt Phosphide with a Conductive Channel for Highly Efficient Electrocatalytic Nitrate Reduction to Ammonia

Electrocatalytic nitrate reduction to ammonia (NO3RR) is regarded as a viable alternative reaction to "Haber Bosch" process. Nevertheless, it remains a major challenge to explore economical and efficient electrocatalysts that deliver high NH3 yield rates and Faraday efficiencies (FE). Here, it demonstrates the fabrication of a 3D core-shell structured Co-carbon nanofibers (CNF)/ZIF-CoP for NO3RR application. Benefitting from the distinct electron transport property of Co-CNF and desirable mass transfer ability from amorphous CoP framework, the as-prepared Co-CNF/ZIF-CoP exhibits large NH3 FE (96.8 +/- 3.4% at -0.1 V vs reversible hydrogen electrode (RHE)) and high yield rate (38.44 +/- 0.65 mg cm-2 h-1 at -0.6 V vs RHE), which are better than Co-CNF/ZIF-crystal CoP. Density functional theory (DFT) calculations further reveal that amorphous CoP presents a lower energy barrier in the rate determination step of the protonation of *NO to produce *NOH intermediates compared with crystal CoP, resulting in a superior NO3RR performance. Eventually, an aqueous galvanic Zn-NO3- battery is assembled by using Co-CNF/ZIF-CoP as cathode material to achieve efficient production of NH3 whilst simultaneously supplying electrical power. This work offers a reliable strategy to construct amorphous metal phosphide framework on conducting CNF as efficient electrocatalyst and enriches its promising application for NO3RR. A facile strategy has been demonstrated to prepare 3D core-shell structured Co-carbon nanofibers (CNF)/ZIF-CoP with amorphous CoP framework derived from ZIF-67 as the shell, which can be used as an efficient NO3RR electrocatalyst, presenting a large NH3 FE (96.8 +/- 3.4% at -0.1 V vs RHE) and high yield rate (38.44 +/- 0.65 mg h-1 cm-2 at -0.6 V vs RHE). The electrocatalytic mechanism reveals that both efficient electron transfer property from Co-CNF and desirable mass transfer ability from amorphous CoP framework contribute to the superior NO3RR performance.image