Photothermal-effect-promoted interfacial OH− filling and the conversion of carrier type in (Co1−xNix)3C during water oxidation

Abstract

The solar-irradiation-induced photothermal effect can accelerate the sluggish kinetics during water oxidation. However, the mechanism describing the photothermal effect is not clear and the range of suitable materials is not well developed, limiting the design and applicability of this technique. Herein, taking a series of (Co_1−xNi_x)₃C (x = 0, 0.1, and 0.2) oxygen evolution reaction (OER) catalysts as model catalysts, the catalytic mechanism of the interfacial photothermal effect (IPE) via concentrated solar irradiation (CSI) is comprehensively uncovered. The temperature/solar irradiation dependence of the polarized cyclic voltammetry (CV) data proves that the chemical basis of the photothermal effects of the catalysts mainly involves enhanced OH⁻ filling at the interface between the catalyst and electrolyte. Hall tests at variable temperatures illustrate that the physical basis for OER enhancement by CSI is that alloyed Ni can cause conversion of the carriers from electrons to holes in Co₃C, leading to enhanced conductivity and light absorption and heat conversion abilities. As a result, (Co_0.8Ni_0.2)₃C exhibits a 660.3% OER enhancement and requires only a 262 mV overpotential to produce a current density of 10 mA cm⁻² under CSI, making it superior to most reported OER catalysts. Also, for the hydrogen evolution reaction (HER), (Co_0.8Ni_0.2)₃C requires only 69 mV to drive a current density of 10 mA cm⁻² under CSI conditions. Finally, this work gives insight into the roots of the photothermal enhancement of OER activity.