MXene supported CoxAy (A = OH, P, Se) electrocatalysts for overall water splitting: unveiling the role of anions in intrinsic activity and stability

The development of efficient and stable bifunctional catalysts that outperform noble metal catalysts is a crucial task and an ongoing challenge for sustainable water electrolysis. In this work, large-size-exfoliated MXene sheets render a flat and flexible platform for the decoration of Co(OH)F, CoP and Co7Se8, allowing them to exhibit high electrocatalytic performances; thanks to the maximized surface area and conductivity. CoP/MXene shows enhanced oxygen evolution reaction (OER) activity, with substantially lower overpotential (η = 230 mV) at 10 mA cm−2 compared to those of IrO2 (300 mV). Furthermore, a hybrid bifunctional electrode (CoP/MXene//CoP/MXene) exhibits highly stable and efficient overall water splitting performance (1.56 V@10 mA cm−2) as compared to the benchmark electrode couple IrO2/C//Pt/C (1.62 V@10 mA cm−2) in alkaline solution. Furthermore, we elucidate the oxidation process of the anion components (P and Se) of the hybrid catalysts under OER conditions and verify their significant influence on the activity and stability. Notably, the surface oxidation of CoP/MXene results in a POx-enriched Co–OOH/CoP/MXene hybrid, which enables retention of consistent activity and stability. On the other hand, SeOx deposition on the Co–OOH/Co7Se8/MXene surface significantly deteriorates the activity and stability of the catalyst. These results not only highlight the insight on the correlation between oxidized anion species and the intrinsic activity of hybridized electrocatalysts but also impart the systematic synthetic design of MXene-supported catalysts with high water-splitting efficiency.