Han-Yi Chen

Designing stable single-atom electrocatalysts with lower energy barriers is urgent for the acidic oxygen evolution reaction. In particular, the atomic catalysts are highly dependent on the kinetically sluggish acid-base mechanism, limiting the reaction paths of intermediates. Herein, we successfully manipulate the steric localization of Ru single atoms at the Co3O4 surface to improve acidic oxygen evolution by precise control of the anchor sites. The delicate structure design can switch the reaction mechanism from the lattice oxygen mechanism (LOM) to the optimized adsorbate evolution mechanism (AEM). In particular, Ru atoms embedded into cation vacancies reveal an optimized mechanism that activates the proton donor-acceptor function (PDAM), demonstrating a new single-atom catalytic pathway to circumvent the classic scaling relationship. Steric interactions with intermediates at the anchored Ru-O-Co interface played a primary role in optimizing the intermediates' conformation and reducing the energy barrier. As a comparison, Ru atoms confined to the surface sites exhibit a lattice oxygen mechanism for the oxygen evolution process. As a result, the delicate atom control of the spatial position presents a 100-fold increase in mass activity from 36.96 A gRu(ads)-1 to 4012.11 A gRu(anc)-1 at 1.50 V. These findings offer new insights into the precise control of single-atom catalytic behavior.

Oxygen reduction reaction (ORR) activity can be effectively tuned by modulating the electron configuration and optimizing the chemical bonds. Herein, a general strategy to optimize the activity of metal single-atoms is achieved by the decoration of metal clusters via a coating–pyrolysis–etching route. In this unique structure, the metal clusters are able to induce electron redistribution and modulate M−N species bond lengths. As a result, M-ACSA@NC exhibits superior ORR activity compared with the nanoparticle-decorated counterparts. The performance enhancement is attributed to the optimized intermediates desorption benefiting from the unique electronic configuration. Theoretical analysis reinforces the significant roles of metal clusters by correlating the ORR activity with cluster-induced charge transfer. As a proof-of-concept, various metal–air batteries assembled with Fe-ACSA@NC deliver remarkable power densities and capacities. This strategy is an effective and universal technique for electron modulation of M−N−C, which shows great potential in application of energy storage devices.

Spinel Co ₃ O ₄ , comprising two types of cobalt ions: one Co ²⁺ in the tetrahedral site (Co ²⁺ _Td ) and the other two Co ³⁺ in the octahedral site (Co ³⁺ _Oh ), has been widely explored as a promising oxygen evolution reaction (OER) catalyst for water electrolysis. However, the roles of two geometrical cobalt ions toward the OER have remained elusive. Here, we investigated the geometrical-site-dependent OER activity of Co ₃ O ₄ catalyst by substituting Co ²⁺ _Td and Co ³⁺ _Oh with inactive Zn ²⁺ and Al ³⁺ , respectively. Following a thorough in operando analysis by electrochemical impedance spectroscopy and X-ray absorption spectroscopy, it was revealed that Co ²⁺ _Td site is responsible for the formation of cobalt oxyhydroxide (CoOOH), which acted as the active site for water oxidation.