Heterogeneous Single Atom Electrocatalysis, Where “Singles” Are “Married”

Abstract

There is an intensive search for heterogeneous single atom catalysts (SACs) of high activity, efficiency, durability, and selectivity for a wide variety of electrocatalytic conversion and chemical reactions, such as the hydrogen evolution reaction (HER), oxygen evolution/reduction reaction (OER and ORR), CO2 reduction reaction (CO2 RR), and nitrogen reduction reaction (NRR). With the downsizing from nanoparticles and clusters to single atoms, there are steady changes in the bond and coordination environment for each and every atom involved. Indeed, the single atoms in these electrocatalysts are not “singles”; they are “married” to the supporting surfaces, and their performance is controlled by the bonding and coordination with the substrate surfaces. Herein, an overview is presented on the brief history leading to the rapid development of SACs and their current status, by focusing on their synthesis, control of composition, strategies to realize single atoms with the desired bonds and coordination, and targeted performance in selected reactions. Their applications in the selected spectrum of energy conversion and chemical reactions are discussed, in relation to their structures at varying length scales down to the atomic level. A particular emphasis is placed on on‐going research activities, together with the future perspectives and particular challenges for SACs.

Efficient Hydrogen Evolution of Oxidized Ni‐N3 Defective Sites for Alkaline Freshwater and Seawater Electrolysis

“…efficient HER. [12][13][14] However, to the best of our knowledge, successful HER application of SACs in alkaline seawater has not been properly realized yet. In addition, the intrinsic HER mechanism of SACs involves rather complicated pathways occurring at the atomically dispersed metal species.…”

Atomic Level Dispersed Metal–Nitrogen–Carbon Catalyst toward Oxygen Reduction Reaction: Synthesis Strategies and Chemical Environmental Regulation

“…In addition, the synergistic effect between single atom sites and atomic clusters is very effective in breaking the limitation of the proportional relationship between electrocatalysis and other types of multi‐step reactions. [ 101‐103 ] In this category of electrocatalyst, a single atom can act as an active catalytic site, and nanoclusters can increase the conductive channels of charge flow in time of an electrochemical reaction.…”

Selective single-atom electrocatalysts: a review with a focus on metal-doped covalent triazine frameworks

“…Recently, single-atom electrocatalysts (SACs), which comprise singly isolated metal atoms immobilized onto a heterogeneous support, have attracted intensive attention as a robust analogue of organometallics. [17][18][19][20][21][22][23][24] SACs are the ultimate form of size reduction of metal electrodes, and they maximize the efficiency of metal atom use. Furthermore, some SACs exhibit unique electrocatalytic activity and selectivity.…”

“…SACs with dened coordination structures on inorganic supports, including nanocarbons, metal oxides, and nitrides, have recently been developed and are well summarized in reviews. 23,24 For example, Kou and Wang et al synthesized single Mo sites with an Mo 1 N 1 C 2 local coordination structure in nitrogen-doped carbons and used them as efficient bifunctional OER/ORR and nitrogen reduction reaction catalysts. 25,26 The same authors nicely demonstrated that the single Co atoms which are coordinated with three Mo atoms in the 2D molybdenum carbide nanosheets served as effective active sites for both the OER and the HER.…”