Lattice‐Confined Ir Clusters on Pd Nanosheets with Charge Redistribution for the Hydrogen Oxidation Reaction under Alkaline Conditions

Abstract

Electrocatalysts with high activity and long‐term stability for the hydrogen oxidation reaction (HOR) under alkaline conditions is still a major challenge for anion exchange membrane fuel cells (AEMFCs). Herein, a heterostructured Ir@Pd electrocatalyst with ultrasmall Ir nanoclusters (NCs) epitaxially confined on Pd nanosheets (NSs) for catalyzing the sluggish alkaline HOR is reported. Apparent charge redistribution occurs across the heterointerface, and both experimental and theoretical results suggest that the electrons transfer from Pd to Ir, which consequently greatly weakens the hydrogen binding on Pd. More interestingly, the interfacial epitaxy results in the formation of Ir/IrO2 Janus nanostructures, where the partially oxidized Ir species away from the interface further optimize the hydroxyl adsorption behavior. The unique Ir@Pd heterostructure eventually shows an optimal balance between hydrogen and hydroxyl adsorption, and hence exhibits impressive HOR activity with an exchange current density of up to 7.18 mA cm–2 in 0.1 m KOH solution. In addition, the Ir@Pd electrocatalyst exhibits negligible activity degradation owing to the confinement effect of the unique epitaxial interface.

Identifying the Role of Hydroxyl Binding Energy in a Non‐Monotonous Behavior of Pd‐Pd4S for Hydrogen Oxidation Reaction

“…Bader charge analysis is used to assess the electron transfer between Pd and Pd 4 S in the Pd-Pd 4 S heterostructure. [23] The calculated results indicate that 0.56 electrons are transferred from Pd to Pd 4 S (Figure 4a), agreeing well with XPS results. Meanwhile, the calculated work function (WF) of Pd (4.95 eV) is lower than that of Pd 4 S (5.01 eV) (Figure 4b and Figure S20, Supporting Information), also implying the electron transfer from Pd to Pd 4 S. [24] Furthermore, the band structures for Pd 4 S, Pd, and Pd-Pd 4 S, indicate that Pd-Pd 4 S has faster charge transfer (Figure S21, Supporting Information).…”

“…[10f,15d] The free energy diagrams of the alkaline HOR pathways on Pd-Pd 4 S, Pd 4 S, and Pd are depicted in Figure 4g. [23,28] Since the HBEs for all catalysts are much stronger than OHBEs, the first HOR steps are H adsorption steps, which are exergonic. Next, the OH adsorption steps are all endothermic, with 0.23 eV for Pd-Pd 4 S, 0.58 eV for Pd 4 S, and 0.68 eV for Pd, respectively.…”

Supported Sub‐Nanometer Clusters for Electrocatalysis Applications

“…The controlled synthesis of sub-nanometer clusters is relatively complicated as compared with the case of NPs because it is difficult to rationally stabilize several targeted atoms on the support, which is more like the metastable mesophase between SACs and NPs. As shown in Figure 2, we highlight several synthetic strategies, including wet-chemical methods, [23][24][25][26][27][28][29] confinement combined with precursor-preselected strategy, [30][31][32][33][34][35][36][37][38] defect-driven deposition, [39][40][41] and electrochemical methods, [42][43][44][45][46][47][48] etc. The general and essential characteristics of those strategies are that the strongly anchored sites on the support should be firstly guaranteed, combining with an appropriate and controllable nucleation process, which enables to precisely control the cluster size and composition by modulating the synthesis parameters.…”

RuO 2 as promoter in Pt‐RuO 2 ‐ nanostructures/carbon composite, a pH ‐universal catalyst for hydrogen evolution/oxidation reactions

“…In alkaline media, first step is the same and the second step is either H ad combine with OH − from the solution or H ad combine with adsorbed OH (OH ad ) to form H 2 O. The two contrasting mechanisms are known for alkaline HOR ‐ (i) Hydrogen binding energy (HBE) theory 28‐33 and (ii) OH ad theory 34‐38 . Understanding the alkaline HER/HOR mechanism is crucial for the development of new HER/HOR catalysts.…”

“…The two contrasting mechanisms are known for alkaline HOR -(i) Hydrogen binding energy (HBE) theory [28][29][30][31][32][33] and (ii) OH ad theory. [34][35][36][37][38] Understanding the alkaline HER/HOR mechanism is crucial for the development of new HER/HOR catalysts. In recent literatures, either HBE or OH adsorption was discussed as the sole descriptor for alkaline HER/HOR.…”