Engineering efficient and sustainable catalysts for hydrogen production through (photo)electrochemical water splitting

Abstract

Hydrogen (H2) is regarded as one of the most important energy sources in the sustainable economy. Water electrolysis emerges as a critical technology for green H2 production based on renewable energy with no carbon emission. To efficiently promote this technology, the thesis concentrates on developing efficient and stable electrocatalysts based on sustainable materials. Sustainable (photo)electrocatalysts studied in this work are expected to be non-toxic, low-cost, and synthesized by environmentally friendly approaches.

The first work concentrated on acidic OECs, the indispensable research pathway to improve the application of green H2 production by proton-exchange-membrane water electrolyzer (PEMWE). Its application is limited by the reliance on noble metals, while non-noble-metal-based OECs usually suffer due to their poor stability in acidic electrolytes with high oxidation potential conditions. Therefore, this work focused on developing stabilization strategies to enhance the stability of earth-abundant-based OECs, along with the activity of catalysts. Firstly, it proposed a nanoscale protective layer to prolong the stability of active cobalt oxide catalysts at near-zero pH conditions. It revealed the acidic corrosion occurring with OECs and the protective effects of the coating layer on the stability of catalysts. Secondly, it utilized the self-healing concept to engineer mixed metal oxide materials. The self-healing concept implies a quasi-equilibrium state where the loss of catalyst due to corrosion occurs at the same or slower rate than its re-electrodeposition.

The second part of this thesis investigated OECs in photoelectrochemical (PEC) water splitting, a complementary device focusing on direct use of solar energy, a clean and renewable source, for green H2 production. Herein, flame-made nanostructured ternary metal oxide, iron tungstate, with surface modification, was proposed as a photoanode based on its narrow bandgap and suitable band edge.