Nitrogen-doped Cobalt Phosphate co-catalyst for efficient photoelectrochemical water oxidation

Abstract

As the consumption of fossil fuel increased tremendously after the industrial revolution, the concentration of carbon dioxide ($CO_2$) in atmosphere has been accumulated by 400 ppm. Carbon dioxide acts as a greenhouse gas, which leads the climate change. One way to solve the climate change problem is to develop the alternative energy source. Photoelectrochemical water splitting or $CO_2$ reduction is a promising technology to deal with the current energy problem. In this study, hematite photoanode is modified with nitrogen-doped cobalt phosphate (Co-Pi) co-catalyst for enhanced photoelectrochemical water oxidation. The photocurrent density of hematite photoanode increases from 0.48 mA/$cm^2$ to 1.01 mA/$cm^2$ at 1.23 vs. RHE under simulated 1-sun (100 mW/$cm^2$) illumination with nitrogen-doped cobalt phosphate. The $N_2$ plasma formed by the microwave plasma enhanced-chemical vapor deposition equipment (MPE-CVD) makes nitrogen atoms dope in Co-Pi co-catalyst. The light absorption properties remain the same after $N_2$ plasma treatment. The electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis show that N-doped Co-Pi lowers the impedance between photoanode and electrolyte, and increases donor density in photoanode.