Hydrogen evolution reaction plays a decisive role in a range of electrochemical and photoelectrochemical devices. It requires efficient and robust electrocatalysts to lower the reaction overpotential and minimize energy consumption. Over the last decade, we have witnessed a rapid rise of new electrocatalysts, particularly those based on non-precious metals. Some of them approach the activity of precious metal benchmarks. Here, we present a comprehensive overview of the recent developments of heterogeneous electrocatalysts for hydrogen evolution reaction. Detailed discussion is organized from precious metals to non-precious metal compounds including alloys, chalcogenides, carbides, nitrides, borides and phosphide, and finally to metal-free materials. Emphasis is placed on the challenges facing these electrocatalysts and solutions for further improving their performance.We conclude with a perspective on the development of future HER electrocatalysts.

The development of non precious metal based electrocatalysts for the hydrogen evolution reaction (HER) holds a decisive key to a spectrum of energy conversion technologies. Previous studies have established layered molybdenum chalcogenides as promising candidates. In this work, we prepared ultrathin MoS2(1–x)Se2x alloy nanoflakes with monolayer or few-layer thickness and fully tunable chemical composition for maximum HER activity. Spectroscopic characterizations corroborate the progressive evolution of their structures and properties as x increases from 0 to 1 without any noticeable phase separation. In particular, it is evidenced that the introduction of selenium continuously modulates the d band electronic structure of molybdenum, probably leading to tuned hydrogen adsorption free energy and consequently electrocatalytic activity. Electrochemical measurements show that all MoS2(1–x)Se2x nanoflakes are highly active and durable for HER with small overpotentials in the range of 80–100 mV and negligible activity loss up to 10000 cycles. Most importantly, alloyed nanoflakes, especially with the chemical composition of MoSSe, exhibit improved performance in comparison to either MoS2 or MoSe2. Given their overall similar nanoflake morphologies, we believe such improvements reflect the higher intrinsic activity of alloyed catalysts with the hydrogen adsorption free energy closer to thermoneutral.

The development of nonprecious metal based electrocatalysts for hydrogen evolution reaction (HER) has received increasing attention over recent years. Previous studies have established MoC as a promising candidate. Nevertheless, its preparation requires high reaction temperature, which more than often causes particle sintering and results in low surface areas. In this study, we show supporting MoC nanoparticles on the three-dimensional scaffold as a possible solution to this challenge and develop a facile two-step preparation method for ∼3 nm MoC nanoparticles uniformly dispersed on carbon microflowers (MoC/NCF) via the self-polymerization of dopamine. The resulting hybrid material possesses large surface areas and a fully open and accessible structure with hierarchical order at different levels. MoO was found to play an important role in inducing the formation of this morphology presumably via its strong chelating interaction with the catechol groups of dopamine. Our electrochemical evaluation demonstrates that MoC/NCF exhibits excellent HER electrocatalytic performance with low onset overpotentials, small Tafel slopes, and excellent cycling stability in both acidic and alkaline solutions.

Active and durable electrocatalysts for methanol oxidation reaction are of critical importance to the commercial viability of direct methanol fuel cell technology. Unfortunately, current methanol oxidation electrocatalysts fall far short of expectations and suffer from rapid activity degradation. Here we report platinum–nickel hydroxide–graphene ternary hybrids as a possible solution to this long-standing issue. The incorporation of highly defective nickel hydroxide nanostructures is believed to play the decisive role in promoting the dissociative adsorption of water molecules and subsequent oxidative removal of carbonaceous poison on neighbouring platinum sites. As a result, the ternary hybrids exhibit exceptional activity and durability towards efficient methanol oxidation reaction. Under periodic reactivations, the hybrids can endure at least 500,000 s with negligible activity loss, which is, to the best of our knowledge, two to three orders of magnitude longer than all available electrocatalysts.