Amorphous cobalt phosphate incorporated in carbon matrix as an efficient pre-catalyst for promoted electrosynthesis of ammonia

Abstract

Developing highly efficient electrocatalysts for nitrate (NO₃⁻) reduction is a promising strategy to realize the eco-friendly and sustainable synthesis of ammonia (NH₃). Currently, some noble metals or earth-abundant metal-based catalysts have been devoted to the electroreduction of nitrate, while the high cost or high bias to achieve the desired faradaic efficiency (FE) hinders their further application. Herein, we report a pre-catalyst featuring amorphous cobalt phosphate incorporated in the carbon matrix (Co–P–O/C) for NO₃⁻ reduction. During the pre-catalytic process, the catalyst undergoes a prominent phase reconstruction with the accumulation of high-valence Co species, obvious P–O bonds, and abundant active sites, which are highly desirable for electrochemical activity. Finally, a 97% FE and high NH₃ yield of 1183 mmol g_cat⁻¹ h⁻¹ was obtained at a low applied potential of −0.2 V vs. reversible hydrogen electrode (RHE) on the optimized Co–P–O/C. In situ Raman spectroscopy and the corresponding X-ray photoelectron spectroscopy (XPS) revealed a conspicuous structural transformation during the electrocatalytic process, which makes a contribution to the energy-efficient NH₃ synthesis. This unique investigation of the amorphous pre-catalyst can inspire its further development in other energy-related electrocatalysis.