Electrocatalytic performance and cell voltage characteristics of 1st-row transition metal phosphate (TM-Pi) catalysts at neutral pH

Abstract

Water electrolysis represents a clean and sustainable route for large-scale hydrogen generation. However, efficient water splitting is hindered by the kinetically sluggish oxygen evolution reaction (OER), which requires significant energy inputs to drive the reaction at sufficiently fast rates. Recently, an increasing number of applications have emerged that require water electrolysis at neutral pH and under ambient conditions. This requirement creates additional challenges as the electrolysis of water is favorable in acidic and alkaline conditions. In order to tackle these challenges, considerable efforts have been devoted to the development of earth-abundant, highly effective, and robust electrocatalysts for the OER at pH = 7. Of these catalysts, amorphous transition-metal phosphates have attracted wide attention because of their unique electrocatalytic properties. In this paper, the OER performance of a series of amorphous first-row transition metal phosphate (TM-Pi) catalysts, namely Co-Pi, NiFe-Pi and Fe-Pi prepared with different deposition strategies onto various substrates, is comparatively studied in a neutral phosphate buffer solution (PBS). Additionally, a simplified cell model is applied to analyze the current-voltage characteristics and quantitatively evaluate and compare the reversible, ohmic, and activation overvoltage components of the studied TM-Pi. It is found that TM-Pi catalysts deposited onto a highly ordered nickel foam (NF) substrate are competitive with commercial Pt and IrO2 catalysts in terms of OER activity and long-term stability.