to conventional energy sources due to its clean nature (i.e., only water is produced upon burning) and high energy density. [2] The electrochemical splitting of water to yield high purity hydrogen (>99.6%) has therefore drawn increasing attention. [3] However, due to the sluggish kinetics of the HER, the use of electrocatalysts is essential in order to reduce the overpotential, especially in alkaline solutions. Although Pt and Pt-based alloys are still benchmark electrocatalysts in the HER, the high cost and low abundance of Pt limits its widespread application in hydrogen production technologies.Recently, a range of abundant transition metal phosphides such as molybdenum phosphide have been intensively examined as potential HER electrocatalysts. Various strategies have been employed to improve the electrocatalytic HER activity of transition metal phosphides, including surface phosphosulfidation, hybridization, and elemental doping. [4] However, despite such modifications, MoP continues to suffer from a high overpotential (>130 mV at 10 mA cm −2 ) [5] and significant instability in alkaline electrolytes. Here we investigate whether the topological states of MoPThe electrolysis processes such as hydrogen evolution reaction (HER) require high efficient catalysts with robust surface stability. A high conductivity is also necessary to speed up the charge transport between the catalyst and the electrolyte. Recently, the observation of exceedingly high conductivity in the topological semimetal MoP, has provided a model catalyst to investigate the correlation between the electrical transport and the electrocatalytic activity for the HER. Thus, MoP is encapsulated in a Mo, P codoped carbon layer (MoP@C). This composite material exhibits outstanding HER performance, with an extremely low overpotential of 49 mV at a current density of 10 mA cm −2 and a Tafel slope of 54 mV dec −1 in an alkaline medium. In addition, electron transport analysis indicates that MoP exhibits high conductivity and mobility due to the existence of triple-point fermions and a complex Fermi surface. Furthermore, the presence of PC and MoC bonds at the interface between the carbon layer and the MoP particles modulates the band structure of MoP@C and facilitates fast electron transfer, accumulation, and subsequent delocalization, which are in turn responsible for the excellent HER activity.

Conductivity, carrier mobility, and a suitable Gibbs free energy are important criteria that determine the performance of catalysts for a hydrogen evolution reaction (HER). However, it is a challenge to combine these factors into a single compound. Herein, we discover a superior electrocatalyst for a HER in the recently identified Dirac nodal arc semimetal PtSn4. The determined turnover frequency (TOF) for each active site of PtSn4 is 1.54 H2 s−1 at 100 mV. This sets a benchmark for HER catalysis on Pt‐based noble metals and earth‐abundant metal catalysts. We make use of the robust surface states of PtSn4 as their electrons can be transferred to the adsorbed hydrogen atoms in the catalytic process more efficiently. In addition, PtSn4 displays excellent chemical and electrochemical stabilities after long‐term exposure in air and long‐time HER stability tests.

No abstract

No abstract