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Highly active and stable electrocatalysts at low cost for hydrogen evolution reaction are essential for large scale hydrogen production. The Ni 3 P-Ni heterostructure confined in 3D networks of carbon nanotube (CNT) has been successfully prepared as the hydrogen evolution reaction (HER) electrode. The morphology and phase composition of Ni 3 P-Ni heterostructure are tunable by varying the acid pickling time. The Ni 3 P-Ni/CNT composite electrode with optimized Ni:Ni 3 P ratio of 22.29 wt% demonstrate high catalytic activity and excellent stability for HER. It demonstrates a comparable HER activity to the standard Pt electrode in alkaline solution, i.e., overpotentials of 116 vs 67 mV at 10 mA·cm−2 and Tafel slops of 59 vs 37 mV·dec−1. No degradation is observed after 1000 cyclic voltammetry (CV) cycles or 50 h operation under constant 0.3 V overpotential. • Pickling affects the morphology of heterogeneous structure and the content of Ni. • The Ni 3 P-Ni heterostructure was anchored to the carbon nanotube network by ball milling. • The electrode was prepared by mixing with PTFE and pressing. • The results show that Ni 3 P-Ni/CNT electrode has the best hydrogen evolution activity when the Ni/Ni 3 P ratio is 22.29 %. [ABSTRACT FROM AUTHOR]