Interface engineering of highly stable CeO2/CoFe@C electrocatalysts for synergistically boosting overall alkaline water splitting performance

Electrochemical water splitting produces "green hydrogen," a clean, sustainable fuel that can eventually contribute to carbon neutrality. However, the big challenge to the widespread adoption of water-splitting technology is the complex synthesis routes that involve harmful or expensive chemicals and sluggish reaction kinetics. This work presents a scalable and environmentally friendly solvent-free strategy for in situ synthesis of highly dispersed CeO2/CoFe nanoparticles encapsulated within 3D hierarchically porous carbon heterostructures (CeO2/CoFe@C) via a simple pyrolysis process. The optimized Ce20/CoFe@C/750 catalyst shows low overpotentials of 114 and 191 mV at 10 mA cm-2 toward the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), respectively, in 1.0 M KOH. Two-electrode systems achieve a cell voltage of 1.508@10 mA cm-2 with robust stability over 500 h in 1.0 M KOH. This notable performance is attributed to the hierarchically porous nanosheet architecture with a superhydrophilic surface that facilitates mass transport, and rapid H2/O2 gas bubble escape, and the synergistically coupled CeO2/CoFe heterointerface and abundant oxygen vacancies boost overall activity, particularly for the OER. Additionally, experimental results indicate that the optimum performance depends critically on the effect of changing Ce concentration. Density functional theory (DFT) calculations suggest that optimizing the CeO2/CoFe interface triggered CeO2 reconstruction, where oxygen migration to CoFe created vacancies. Also, this reduction of the Ce site at the interface and the availability of d and f orbitals contribute to bonding and antibonding adsorbates, thereby moderating their adsorption energy and boosting OER activity. This study demonstrates the significance of rational design concepts in catalyst structure optimization, resulting in noticeably improved overall water-splitting performance.