N-doped TiO₂ nanotube arrays with uniformly embedded Co_xP nanoparticles for high-efficiency hydrogen evolution reaction

Efficient and stable non-precious metal based electrocatalysts are crucial to the hydrogen evolution reaction (HER) in renewable energy conversion. Herein, Co_xP nanoparticles (NPs) are uniformly embedded in N-doped TiO₂ nanotube arrays (Co_xP/N-TiO₂ NTAs) by low-temperature phosphorization of the precursor of metallic cobalt NPs embedded in N-doped TiO₂ NTAs (Co/N-TiO₂ NTAs) which were fabricated by phase separation of CoTiO₃ NTAs in ammonia. Owing to the abundant exposed surface active sites of Co_xP NPs, tight contact between the Co_xP NPs and TiO₂ NTAs, fast electron transfer in N-doped TiO₂, and channels for effective diffusion of ions and H₂ bubbles in the tubular structure, the Co_xP/N-TiO₂ NTAs have excellent electrocatalytic activity in HER exemplified by a low overpotential of 180 mV at 10 mA cm⁻² and small Tafel slope of 51 mV dec⁻¹ in 0.5 M H₂SO₄. The catalyst also shows long-term cycling stability and is a promising non-precious metal catalyst for HER.