• Energy Research

AbstractOwing to the rapidly increasing consumption of fossil fuels, finding clean and reliable new energy sources is of the utmost importance. Thus, developing highly efficient and low‐cost catalysts for electrochemical reactions in energy conversion devices is crucial. Single‐atom catalysts (SACs) with maximum metal atom utilization efficiency and superior catalytic performance have attracted significant attention, especially for electrochemical reactions. However, because of the highly unsaturated coordination environment, the stability of SACs can be a challenge for practical applications. In this review, we will summarize the strategies to increase the stability of SACs and synthesizing stable SACs, as well as the application of SACs in electrochemical reactions. Finally, we offer a perspective on the development of advanced SACs through rational design and a deeper understanding of SACs with the help of in situ or operando techniques in electrochemical reactions.

AbstractOwing to the rapidly increasing consumption of fossil fuels, finding clean and reliable new energy sources is of the utmost importance. Thus, developing highly efficient and low‐cost catalysts for electrochemical reactions in energy conversion devices is crucial. Single‐atom catalysts (SACs) with maximum metal atom utilization efficiency and superior catalytic performance have attracted significant attention, especially for electrochemical reactions. However, because of the highly unsaturated coordination environment, the stability of SACs can be a challenge for practical applications. In this review, we will summarize the strategies to increase the stability of SACs and synthesizing stable SACs, as well as the application of SACs in electrochemical reactions. Finally, we offer a perspective on the development of advanced SACs through rational design and a deeper understanding of SACs with the help of in situ or operando techniques in electrochemical reactions.

AbstractPt‐Ir catalysts have been widely applied in unitized regenerative fuel cells due to their great activity for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, the application of noble metals is seriously hindered by their high cost and low abundance. To reduce the noble metals loading and catalyst cost, the atomic layer deposition is applied to selectively surface anchoring of Ir single atoms (SA) on Pt nanoparticles (NP). With the formation of SA‐NP composite structure, the IrSA‐PtNP catalyst exhibits significantly improved performance, achieving 2.0‐ and 90‐times mass activity by comparison with the benchmark Pt/C catalyst for the ORR and OER, respectively. Density functional theory calculations indicate that the SA‐NP cooperation synergy endows the IrSA‐PtNP catalyst to surpass the bifunctional catalytic activity limit of Pt‐Ir NPs. This work provides a novel strategy for the construction of high‐performing dual catalyst through designing the single atom anchoring on NPs.image

AbstractPt‐Ir catalysts have been widely applied in unitized regenerative fuel cells due to their great activity for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, the application of noble metals is seriously hindered by their high cost and low abundance. To reduce the noble metals loading and catalyst cost, the atomic layer deposition is applied to selectively surface anchoring of Ir single atoms (SA) on Pt nanoparticles (NP). With the formation of SA‐NP composite structure, the IrSA‐PtNP catalyst exhibits significantly improved performance, achieving 2.0‐ and 90‐times mass activity by comparison with the benchmark Pt/C catalyst for the ORR and OER, respectively. Density functional theory calculations indicate that the SA‐NP cooperation synergy endows the IrSA‐PtNP catalyst to surpass the bifunctional catalytic activity limit of Pt‐Ir NPs. This work provides a novel strategy for the construction of high‐performing dual catalyst through designing the single atom anchoring on NPs.image

AbstractA fuel cell is an energy conversion device that can continuously input fuel and oxidant into the device through an electrochemical reaction to release electrical energy. Although noble metals show good activity in fuel cell‐related electrochemical reactions, their ever‐increasing price considerably hinders their industrial application. Improvement of atom utilization efficiency is considered one of the most effective strategies to improve the mass activity of catalysts, and this allows for the use of fewer catalysts, saving greatly on the cost. Thus, single‐atom catalysts (SACs) with an atom utilization efficiency of 100% have been widely developed, which show remarkable performance in fuel cells. In this review, we will describe recent progress on the development of SACs for membrane electrode assembly of fuel cell applications. First, we will introduce several effective routes for the synthesis of SACs. The reaction mechanism of the involved reactions will also be introduced as it is highly determinant of the final activity. Then, we will systematically summarize the application of Pt group metal (PGM) and nonprecious group metal (non‐PGM) catalysts in membrane electrode assembly of fuel cells. This review will offer numerous experiences for developing potential industrialized fuel cell catalysts in the future.

AbstractA fuel cell is an energy conversion device that can continuously input fuel and oxidant into the device through an electrochemical reaction to release electrical energy. Although noble metals show good activity in fuel cell‐related electrochemical reactions, their ever‐increasing price considerably hinders their industrial application. Improvement of atom utilization efficiency is considered one of the most effective strategies to improve the mass activity of catalysts, and this allows for the use of fewer catalysts, saving greatly on the cost. Thus, single‐atom catalysts (SACs) with an atom utilization efficiency of 100% have been widely developed, which show remarkable performance in fuel cells. In this review, we will describe recent progress on the development of SACs for membrane electrode assembly of fuel cell applications. First, we will introduce several effective routes for the synthesis of SACs. The reaction mechanism of the involved reactions will also be introduced as it is highly determinant of the final activity. Then, we will systematically summarize the application of Pt group metal (PGM) and nonprecious group metal (non‐PGM) catalysts in membrane electrode assembly of fuel cells. This review will offer numerous experiences for developing potential industrialized fuel cell catalysts in the future.

Alkaline water splitting is an attractive method for sustainable hydrogen production.

Alkaline water splitting is an attractive method for sustainable hydrogen production.

AbstractThe high‐temperature pyrolysis process for preparing M–N–C single‐atom catalyst usually results in high heterogeneity in product structure concurrently contains multiscale metal phases from single atoms (SAs), atomic clusters to nanoparticles. Therefore, understanding the interactions among these components, especially the synergistic effects between single atomic sites and cluster sites, is crucial for improving the oxygen reduction reaction (ORR) activity of M–N–C catalysts. Accordingly, herein, we constructed a model catalyst composed of both atomically dispersed FeN4 SA sites and adjacent Fe clusters through a site occupation strategy. We found that the Fe clusters can optimize the adsorption strength of oxygen reduction intermediates on FeN4 SA sites by introducing electron‐withdrawing –OH ligands and decreasing the d‐band center of the Fe center. The as‐developed catalyst exhibits encouraging ORR activity with half‐wave potentials (E1/2) of 0.831 and 0.905 V in acidic and alkaline media, respectively. Moreover, the catalyst also represents excellent durability exceeding that of Fe–N–C SA catalyst. The practical application of Fe(Cd)–CNx catalyst is further validated by its superior activity and stability in a metal–air battery device. Our work exhibits the great potential of synergistic effects between multiphase metal species for improvements of single‐atom site catalysts.