Tuning the Spin Density of Cobalt Single-Atom Catalysts for Efficient Oxygen Evolution

Abstract

Single-atom catalysts (SACs) with magnetic elements as the active center have been widely exploited for efficient electrochemical conversions. Understanding the catalytic role of spin, and thus modulating the spin density of a single-atom center, is of profound fundamental interest and technological impact. Here, we synthesized ferromagnetic single Co atom catalysts on TaS2 monolayers (Co1/TaS2) as a model system to explore the spin–activity correlation for the oxygen evolution reaction (OER). A single Co atom adsorbed at the hollow site (CoHS) with spin-polarized electronic states serves as the active site for OER, whose spin density can be regulated by its neighboring single Co site via tuning the Co loading. Both experimental and theoretical results reveal the spin density-dependent OER activity that an optimal spin density of CoHS can be achieved with a neighboring hetero-single CoTa site (substitution of Ta by Co) for a superior OER performance, in contrast to a homo-single CoHS site, which creates an excessive spin density over vicinal CoHS. An optimized spin density of CoHS results in an optimal binding energy of oxygen species for the OER. Establishing the spin–activity correlation in SACs may create a descriptor for designing efficient magnetic SACs for renewable energy conversions.

Understanding Single-Atom Catalysis in View of Theory

“… 103 The spin–activity correlation in a single Co atom supported by TaS 2 -catalyzed oxygen evolution reaction was also reported in a combined experimental and theoretical work. 104 By using ab initio nonadiabatic molecular dynamics simulations, Cheng et al found the spin selection could enhance charge carrier lifetimes and thus boost the reaction in a photocatalytic water-splitting reaction catalyzed by single copper atoms on Anatase TiO 2 . 105 Both experiments and simulations have demonstrated that the rational modulating spin states of SACs is a promising method to boost the catalytic performance.…”

“…Very recently, Gong et al successfully fabricated the single Co atoms centered in porphyrin units of covalent organic frameworks (COFs), COF-367-Co. 102 They found that by rationally regulating the oxidation states of single Co atoms such as Co II -TAP and Co III -TAP, as shown in Figure 7a 103 The spin−activity correlation in a single Co atom supported by TaS 2 -catalyzed oxygen evolution reaction was also reported in a combined experimental and theoretical work. 104 By using ab initio nonadiabatic molecular dynamics simulations, Cheng et al found the spin selection could enhance charge carrier lifetimes and thus boost the reaction in a photocatalytic water-splitting reaction catalyzed by single copper atoms on Anatase TiO 2 . 105 Both experiments and simulations have demonstrated that the rational modulating spin states of SACs is a promising method to boost the catalytic performance.…”

Hollow Carbon Nanoballs on Graphene as Metal‐Free Catalyst for Overall Electrochemical Water Splitting

“…[15][16][17] More recently, a great deal of effort has been made to develop single-atom electrocatalysts (SACs) with excellent atom-utilization efficiency to address the abovementioned issues and accelerate water electrolysis. [18][19][20] However, SACs face several of their own drawbacks such as low volume of production, the complex equipment, and extremely controlled conditions required, ambiguous number of active site as well as their high cost which unfavorable to use it in large scale. [21] Besides these catalysts, metal-free nitrogenous carbon catalysts have received enormous interest and have already shown their potential to be used as the replacement for expensive metallic catalysts in FCs and water splitting cells [22][23][24][25] due to their low cost, huge surface area, desirable chemical stability, high electrical conductivity, remarkable resistance to CO poisoning, and multifunctionality.…”

Structural rule of N-coordinated single-atom catalysts for electrochemical CO2 reduction

“…), 8–13 SACs contribute an excellent platform to explore great potential catalysts for different catalytic reactions, e.g. , water splitting, 14–16 nitrogen reduction reaction (NRR) 17–20 and carbon dioxide reduction reaction (CO 2 RR). 21–24 In these SACs, nitrogen (N) atoms are the common ligands used to anchor transition metal centers (TM); thus, the N-coordination environment (denoted as N x , where x is the N-coordination number) is of great importance to determine the catalytic performance of TM SACs.…”