Size effect of carbon nanotubes confined CoP–Ni 2 P heterostructure via phosphorylation‐induction strategy for efficient overall water splitting

Abstract The size tuning of one‐dimensional (1D) spatially confined electrocatalysts with abundant exposed active sites is still a huge challenge for electrocatalytic hydrogen/oxygen evolution reactions (HER/OER) and overall water splitting (OWS). Herein, we construct CoP–Ni 2 P heterostructure embedded ultrafine N‐doped carbon nanotubes (CoP–Ni 2 P@U‐NCNTs/NF) with a diameter size of about 50 nm from 2D cobalt‐based zeolitic imidazolate framework (Co‐ZIF‐L/NF) via phosphorylation strategy, while Co–Ni embedded N‐doped carbon nanotubes with a diameter of about 200 nm are constructed via carbonization. The size‐tuned CoP‐Ni 2 P@U‐NCNTs/NF possesses abundant active sites and electron transport pathways, and the stability of CoP–Ni 2 P heterostructure is improved by carbon coating. Density functional theory (DFT) calculation results verify that the Ni 2 P and CoP heterojunction synergistically promotes the electron redistribution of the Co–Ni to optimize Gibbs free energy of H* (Δ G H* ). Meanwhile, the NCNTs‐confined CoP–Ni 2 P induced by phosphating accelerates the reconstruction of the CoOOH‐NiOOH compared with Ni‐Co, thereby boosting the reaction kinetics of efficient OWS due to the reduced reaction energy barrier of O–O coupling. As expected, the CoP–Ni 2 P@U‐NCNTs/NF favors a low overpotential of 67/203 mV@10 mA cm −2 for the HER/OER, realizing an ultralow cell voltage of 1.52 V@10 mA cm −2 for OWS and long‐term durability at various current densities. This work provides a feasible approach to tuning the composition and structure of high‐efficiency electrocatalysts for the production of green hydrogen.