Dynamic Coordination Structure Evolutions of Atomically Dispersed Metal Catalysts for Electrocatalytic Reactions

Abstract

and high-efficient renewable energy conversion devices such as fuel cells and batteries. Hence, the development of costeffective catalysts in facilitating various electrocatalytic reactions with high activity and selectivity is urgently needed. [2,3] In the last two decades, nanoparticles have been preferred as the efficient catalysts for various heterogeneous catalysis process. [4,5] However, it should be noted that only the surface atoms would participate in the electrocatalysis process, while metal atoms embedded in nanoparticles cannot be fully utilized. Hence, downsizing the metal sizes of nanoparticles to atomically dispersed metal atoms to form single-atom catalysts (SACs) is a promising strategy, which aims to achieve a comparable electrocatalytic performance to nanoparticles but with maximized atom efficiency and greatly reduced cost of catalyst preparation. [5][6][7] The concept of "SACs" was first developed in heterogeneous catalysis by Zhang et al. in 2011, they used coprecipitation method to synthesize isolated Pt single atoms anchored onto FeO substrates, which exhibited extraordinary activity in CO oxidation. [8] This pioneering work sheds light on using SACs as promising electrocatalysts for the improved activity in the crucial energy-conversion electrochemical reactions.Due to the extremely high surface energy, the single metal atoms in SACs are likely to migrate and aggregate under synthetic and electrocatalytic conditions, and they are generally stabilized by a support matrix such as MOFs [9,10] and graphene-like carbon nitride. [11][12][13] Therefore, the interaction of the single-atom sites with the ideal supports and the electronic properties of SACs can be regulated through changing the host or doping heteroatom. Note that, the metal sites and local coordination environments including the metal-support interaction (MSI) play a crucial synergistic role in dominating electrocatalytic reactions, which is closely correlated to the activity and stability of SACs. [14] Hence, understanding the coordination structure-performance correlation in SACs is the paramount guidance for the development of highly efficient SACs for electrocatalytic reactions.Although many breakthroughs on fabrication strategies and characterization techniques of SACs in various electrocatalytic reactions have been recorded, [15][16][17][18][19][20] a deeper understanding of the dynamic nature of single metal active sites with local coordination structures under realistic working conditions is still poorly studied. In most studies, the isolated metal centers in the SACs with the static atomic configurations based on ex situ Single-atom catalysts (SACs) are regarded as promising electrocatalysts for various reactions in the field of energy conversion and storage owing to their maximized atom utilization efficiency and unique electronic properties. The modifications of local coordination structures of single metal centers play significant roles in dominating catalytic performances, thus the SACs are resurveyed with different l...

Single-Atom Catalysts on Covalent Organic Frameworks for Energy Applications

“…Therefore, rapid electron transfer is one of the critical requirements to promote reactivity. 124 In this sense, Lotsh et al reported conjugated azine-linked N 2 -COF as a photosensitizer and chloro(pyridine)cobaloxime as a cocatalyst, where a H 2 generation rate of 782 μmol g −1 h −1 is achieved. 125 Later, structural features such as COF crystallinity, porosity, metal sites, and overall electronic structures were explored and tuned, considering the photocatalytic performance.…”

“…In an alkaline aqueous solution, the half-reaction is expressed as 2H 2 O + 2e – → 2OH – + H 2 , while in an acidic solution, the reaction is expressed as 2H + + 2e – → H 2 . Therefore, rapid electron transfer is one of the critical requirements to promote reactivity . In this sense, Lotsh et al reported conjugated azine-linked N 2 -COF as a photosensitizer and chloro(pyridine)cobaloxime as a cocatalyst, where a H 2 generation rate of 782 μmol g –1 h –1 is achieved .…”

Spatially and temporally understanding dynamic solid–electrolyte interfaces in carbon dioxide electroreduction

“…The catalyst restructuring under electrochemical working conditions has been commonly observed for various reactions and across different scales (from nanoscopic to macroscopic). [38][39][40][41][42] From the viewpoint of thermodynamics based on the Nernst equation, the stable phase of a catalyst under electrochemical conditions is mainly determined by pH, electrode potential, and ionic concentration. In particular, the application of potential bias relevant to CO 2 RR provides an energy input that accompanies drastic structural reconstruction, which is the main driving force for the observed changes in structures and/or morphologies.…”

Gaining Deep Understanding of Electrochemical CO2RR with In Situ/Operando Techniques

“…Typically, the coordination structure of single-atom catalysts can significantly affect adsorption behavior of intermediates, and thus change product distributions. [150] Tang and co-workers studied the effects of coordination environment regulation on the CO 2 RR performance of Ni single-atom catalysts on C, N, or B codoped graphene using DFT calculations. [151] The results reveal that the linear scaling relationship between *COOH and *CO is weakened via a specific coordination environment induced by C, N, or B co-doping.…”