Recent Progress in Non‐Precious Metal Single Atomic Catalysts for Solar and Non‐Solar Driven Hydrogen Evolution Reaction

Abstract

converting electrical energy into chemical energy. However, both reactions require large thermodynamic overpotential to overcome the kinetic barriers. [3] The cathodic reaction of HER has received extensive attentions for hydrogen production. To improve the efficiency of electrical energy to hydrogen production, the cathodic overpotentials have to be reduced, especially at high current densities for practical application. This can be achieved via catalysts, which include transition metals and their sulfides, nitrides, phosphides, selenides, and carbides. [4] Direct solar-driven water splitting is a more sustainable and renewable strategy compared to water electrolysis. As a highly desirable approach to solve the energy crisis, it collects and stores solar energy in chemical bonds. [5] In the solar-driven water splitting reaction, a semiconductor is required to absorb radiant energies, generate electron-hole pairs, and finally drive the decomposition of water. [5] Therefore, quantum efficiency of this process is determined by the semiconductors. P-type semiconductors, for example, p-InP and Cu 2 O, with high position of conduction band, can reduce protons into hydrogen as a photocathode. However, solar to hydrogen (STH) efficiency is largely dependent on the surface reaction kinetics to some extent. [6] Solar water splitting has attracted intensive attention of researchers since the first report in 1972. [7] Its practical implementation encounters many challenges, one of which is to develop highly active sites on the bare semiconductor surface to lower HER barrier. [8] One approach to introduce catalytic active center is to coat isolated metallic nanoparticles as catalysts on the surface. [9] For instance, p-InP coated with Rh particles could yield 13.3% conversion efficiency to hydrogen. [10] The improvement is ascribed to the change of Schottky barrier height of the material system through addition of metal particles. [11] With higher density of majority carriers than the semiconductors, the metals on the surface enable facile transport of minority carriers and facilitate reduction reaction. [5] Another effective approach to overcome the kinetic limitation of solar-assisted water splitting is to provide an extra bias which helps the photogenerated electron-hole pairs separate and migrate to the electrode surface. [12] Besides, the additional bias can lead bending of the semiconductor's band and hence compensate the insufficient electronic energy and overcome the

Single-atom catalysts for photocatalytic energy conversion

“…The unsaturated active sites in SACs enable optimizing the adsorption of molecules by tuning the For the utilization of infinite and freely accessible solar energy, artificial photocatalytic energy conversion provides a promising strategy to overcome the global energy crisis and combat the increasingly erratic climate by reducing greenhouse gas emissions. 24,25 For example, photocatalytic water splitting is a technologically straightforward and cost-competitive avenue toward sustainable clean H 2 fuel production, [26][27][28] while photocatalytic CO 2 reduction represents a deployable and highly attractive strategy to convert inert CO 2 into value-added chemicals and definitively close down the carbon cycle. 11,24,[29][30][31] Nevertheless, the performance of the traditional photocatalytic systems, which greatly rely upon the energy band configuration and surface structure of the catalysts, is still far from satisfactory because of the sluggish separation of electron-hole pairs and limited surface-active sites.…”

“…Furthermore, due to the limited electron penetrability of microscopic techniques, isolated metal atoms decorated in the bulk phase or cavities instead of the surface structure are difficult to be observed. 28 Consequently, some additional spectroscopic methods are necessary to provide complementary data and underpin the presence of isolated metal sites in single-atom photocatalysts.…”

Recent progress on the long‐term stability of hydrogen evolution reaction electrocatalysts

“…12,137,138 Single-atom catalysts have attracted much attention due to their high atomic efficiency, and the related work of Ni single-atom supported on carbon supports also shows strong stability. 152 Ni single-atoms anchored to nanoporous graphene (Ni-doped np-G), which still maintained 90% of the initial activity after 120 h of continuous operation at 150 mV overpotential in 0.5 M H 2 SO 4 , showing outstanding stability (Figure 9A). 142 The experiment and theoretical calculation results agree that the structure and morphology of Ni-doped np-G catalysts are stable (Figure 9B).…”

“…In recent years, many reports focused on the in‐depth study of the HER stability of nickel monomers and nickel‐based complexes 12,137,138 . Single‐atom catalysts have attracted much attention due to their high atomic efficiency, and the related work of Ni single‐atom supported on carbon supports also shows strong stability 152 . Ni single‐atoms anchored to nanoporous graphene (Ni‐doped np‐G), which still maintained 90% of the initial activity after 120 h of continuous operation at 150 mV overpotential in 0.5 M H 2 SO 4 , showing outstanding stability (Figure 9A).…”

Machine learning for design principles for single atom catalysts towards electrochemical reactions

“…187 ML, however, can accelerate the screening of SACs and decrease the computational cost and time by screening for similarities in SACs and establishing deep structure-activity relationships. 146,[188][189][190] Therefore, the integration of ML algorithms and DFT calculations has been performed for the rapid and highthroughput screening of SACs. 191 For example, ML combined DFT calculations were employed to screen and design MBenebased SACs for the HER.…”