Synergistic effects of metallic and non-metallic element-doped electrocatalysts for the hydrogen evolution reaction: a review

, P, N, B, O, S) elements has emerged as an effective strategy to enhance catalytic activity. This dual-doping approach enables fine-tuning of the catalyst's electronic environment, increases active site density, and improves hydrogen adsorption/desorption behaviour. Metallic dopants modulate conductivity and the electronic structure of active sites, while non-metallic heteroatoms introduce charge redistribution, surface defects, and chemical polarity - collectively accelerating HER kinetics. This review critically examines recent advances in the synthesis and performance of heteroatom-doped HER electrocatalysts under acidic and alkaline conditions. Emphasis is placed on how compositional tuning, structural design, and interface engineering contribute to improved catalytic performance, including low overpotentials, favourable Tafel slopes, and long-term stability. These developments underscore the potential of heteroatom doping as a versatile platform for designing next-generation HER catalysts for scalable and economically viable hydrogen energy systems.