Interface engineering to optimize the catalytic activity of Fe, Co, and Ti sites in FeCoP/MXene toward efficient overall water splitting

Abstract

Transition metal phosphides (TMPs), with tunable electronic structures and diverse compositions, are promising candidates for electrocatalytic water splitting. However, their unsatisfactory electrical conductivity and tendency to aggregate during reactions result in structural instability, ultimately hindering further improvement of their electrocatalytic performance. To address these issues, a bamboo-leaf-like FeCoP/MXene heterojunction was synthesized by hydrothermal and thermal treatments, utilizing highly conductive MXene as the substrate. Density functional theory (DFT) calculations and experimental characterization reveal that strong Ti–O–Co/Fe covalent bond are formed between MXene and FeCoP through hybridization of O 2p and Co/Fe 3d orbitals, which enhance the structural stability of the interface and facilitate the effective anchoring of FeCoP on the MXene surface. Consequently, the structural stability and electrical conductivity of the catalyst are improved simultaneously. Additionally, interfacial charge redistribution optimizes the Gibbs free energy of hydrogen adsorption at the Co, Fe, and Ti sites while promoting the adsorption and activation of water molecules. These factors interact synergistically, leading to enhanced bi-functional electrocatalytic performance for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In a FeCoP/MXene (+||−) two-electrode system, the catalyst achieves a current density of 10 mA cm^–2 at a potential of 1.5 V, which is superior to the RuO₂ (+)||Pt/C (−) system. The assembled water splitting device exhibits long-term stability for up to 100 h at a current density of 100 mA cm^–2. Furthermore, an anion exchange membrane water electrolyzer (AEMWE) equipped with FeCoP/MXene as both anode and cathode achieves an industrial-grade current density of 500 mA cm^–2 at 1.83 V. These results highlight the critical role of interfacial engineering in enhancing the electrocatalytic performance of TMPs for water splitting and provide valuable insights for the design of novel bifunctional TMP catalysts.

Graphical abstract