Tailoring Interfacial Charge Transfer of Epitaxially Grown Ir Clusters for Boosting Hydrogen Oxidation Reaction

Abstract

The sluggish kinetics of hydrogen oxidation reaction (HOR) is one of the critical challenges for anion exchange membrane fuel cells. Here, we report epitaxial growth of Ir nanoclusters (<2 nm) on a MoS2 surface (Ir/MoS2) and optimize the alkaline HOR activity via tailoring interfacial charge transfer between Ir clusters and MoS2. The electron transfer from MoS2 to Ir clusters can effectively prevent the oxidation of Ir clusters, which is not the case for carbon‐supported Ir nanoclusters (Ir/C) synthesized using the same method. Moreover, the HOR performance of the Ir/MoS2 can be further optimized by tuning the hydrogen binding energy (HBE) via a precise annealing treatment. A substantial exchange current density of 1.28 mA cmECSA−2 is achieved in the alkaline medium, which is ∼10 times over that of Ir/C. The HOR mass‐specific activity of Ir/MoS2 heterostructure is as high as 182 mA mgIr−1. The experimental results and density functional theory calculations reveal that the significant improved HOR activity is attributed to the decreased HBE, which highlights epitaxial growth is an effective way for boosting catalytic activity of heterostructured catalysts.

Electric-Double-Layer Origin of the Kinetic pH Effect of Hydrogen Electrocatalysis Revealed by a Universal Hydroxide Adsorption-Dependent Inflection-Point Behavior

“…Yan and colleagues recently have shown that the hydrogen binding energies (HBEs), as indicated by the voltammetric peaks associated with the underpotential deposition hydrogen (H upd ), reasonably account for the nearly linear decrease in specific activities for HOR/HER on a variety of polycrystal noble metal catalysts with the increasing electrolyte pH. − These facts seem to strengthen the general idea that the HBEs can serve as the sole activity descriptor of catalysts for HOR/HER, while hydroxide binding energies (OHBEs) have trivial impact. On the other hand, results from experiments and simulations challenging this idea are as common as those that support it. − Numerous studies have shown that the activity for HOR/HER in alkaline media can be promoted by increasing the OHBE/oxophilicity of the catalyst surface, for example, modification of Pt with oxophilic Ni­(OH) 2 islands or Ru atoms. ,− On this basis, Markovic et al have proposed the bifunctional mechanism for hydrogen electrode reactions that highlights the crucial role of OHBE toward the dissociation and/or formation of interfacial H 2 O molecules. , In addition, McCrum and Koper have shown, through both experimental observation and theoretical model, that the kinetics of HER should also have volcano dependences on OHBE owing to the switch of the rate-determining step from water dissociation to OH ad desorption with increasing OHBE . More importantly, they reckoned that the activation barrier of water dissociation is linearly related to the OHBE of catalysts, no matter whether the OH ad is involved or not.…”

Prominent electronic effect in iridium-alloy-skinned nickel nanoparticles boosts alkaline hydrogen electrocatalysis

“…2(d) and Table S2 (ESI†) summarize and compare the two mass-specific values of different precious metal based HOR electrocatalysts reported in the literature as well as the commercial benchmark catalysts. 12,14,23–36 Remarkably, the j k,m value of our Ni@IrNi is about four-fold greater than those of 20 wt% Ir/C and 20 wt% Pt/C, and significantly exceeds that of 20 wt% PtRu/C; its j 0,m value is about twice greater than those of 20 wt% Ir/C and 20 wt% Pt/C as well as 20 wt% PtRu/C (Fig. S13, ESI†).…”

“…the literature as well as the commercial benchmark catalysts. 12,14,[23][24][25][26][27][28][29][30][31][32][33][34][35][36] Remarkably, the j k,m value of our Ni@IrNi is about four-fold greater than those of 20 wt% Ir/C and 20 wt% Pt/C, and significantly exceeds that of 20 wt% PtRu/C; its j 0,m value is about twice greater than those of 20 wt% Ir/C and 20 wt% Pt/C as well as 20 wt% PtRu/C (Fig. S13, ESI †).…”

“…Surprisingly, our Ni@IrNi remains highly HOR active over a wide working potential window of up to 1.0 V, which is the most positive working potential ever measured for Ir-based materials. [11][12][13][14] It indicates that alloying with Ni likely retards the surface oxidation of Ir and preserves its activity under highly anodic potentials, even though the underlying mechanism needs to be further elucidated. To investigate the possible role of metallic Ni cores in Ni@IrNi, we selectively etch the metallic cores using HCl (denoted as e-Ni@IrNi) (Fig.…”

“…13 It also has a relatively narrow HOR working potential window, and suffers from an activity decline beyond 0.4 V (versus the reversible hydrogen electrode or RHE) owing to surface oxidation. 11,13,14 Alloying with a suitable secondary element is a possible strategy to rationally modulate electronic structures, fine-tune surface affinities towards key reaction intermediates, and thereby achieve performances not attainable with single-component catalysts. 15,16 Alloying can also lower the usage of precious metals, and render such catalysts more amenable to practical applications.…”