Modulating Water Splitting Kinetics via Charge Transfer and Interfacial Hydrogen Spillover Effect for Robust Hydrogen Evolution Catalysis in Alkaline Media

Abstract Designing and synthesizing advanced electrocatalysts with superior intrinsic activity toward hydrogen evolution reaction (HER) in alkaline media is critical for the hydrogen economy. Herein, a novel Ir@Rhene heterojunction electrocatalyst is synthesized via epitaxially confining ultrasmall and low‐coordinate Ir nanoclusters on the ultrathin Rh metallene accompanying the formation of Ir/IrO2 Janus nanoparticles. The as‐prepared heterojunctions display outstanding alkaline HER activity, with an overpotential of only 17 mV at 10 mA cm−2 and an ultralow Tafel slope of 14.7 mV dec−1. Both structural characterizations and theoretical calculations demonstrate that the Ir@Rhene heterointerfaces induce charge density redistribution, resulting in the increment of the electron density around the O atoms in the IrO2 site and thus delivering much lower water dissociation energy. In addition, the dual‐site synergetic effects between IrO2 and Ir/Rh interface trigger and improve the interfacial hydrogen spillover, thereby subtly avoiding the steric blocking of the active site and eventually accelerating the alkaline HER kinetics.


Supplementary Results
(Caution: the flow rate of H2 gas must be controlled at lower flow velocity due to the produced spark and the risk of hydrogen gas burning).For the IrO2/C, 2.6 mg IrO2 and 10.4 mg XC-72 substrates were thoroughly dispersed in a mixture solution containing 1.543 mL of ethanol, 1.543 mL of DI water, and 0.163 mL Nafion solution to prepare catalyst ink (4 mg mL -1 ).
For the Ir-IrO2/C, 12 mg Ir/C and 2.4 mg IrO2 were thoroughly dispersed in a mixture solution containing 1.71 mL of ethanol, 1.71 mL of DI water, and 0.18 mL of Nafion solution to prepare catalyst ink (4 mg mL -1 ).

Figure S1 .
Figure S1.Characterization of Rhenes.(a, b) SEM images, (c) low-magnification TEM image, (d) TEM image of Rhene after beam exposure for 5 s and (e) corresponding high-resolution TEM image, and (f) AFM image and corresponding height profile.

Figure S7 .
Figure S7.Current-potential curve of Pt plate in highly pure H2-saturated 1.0 M KOH electrolyte, used for calibration of the Hg/HgO electrode with respect to RHE.Scan rate: 1 mV s -1 .

Figure S12 .
Figure S12.The determination of interfacial hydrogen spillover for Ir@Rhene.a) the photographic image of WO3 before and after H2 treatment at room temperature (25 o C), observing that the WO3 does not undergo an observable color change.b) the photographic image of physically mixed materials for WO3 and Ir@Rhene before and after H2 treatment at room temperature (25 o C), clearly showing the color change from yellow to blue green.

Figure S14 .
Figure S14.SEM images and corresponding EDS-mapping images of the Ir@Rhene/C on carbon paper after durability measurement.

Figure S15 .
Figure S15.Theoretical model of Ir-Rhene, showing the a) oblique view, b) front view, and c) top view of model.

Figure S17 .
Figure S17.The optimized configurations of water adsorption (H2O*) on the (a) Rh site, (b) Ir site, (c) IrO2 site, and (d) Ir/Rh interface site of Ir@Rhene model, showing both the top view and front view of each structure, as well as the corresponding adsorption energy (Eads).

Figure S18 .
Figure S18.Atomic configurations of Ir@Rhene during the H2O dissociation into OH* and H*.

Figure S21 .
Figure S21.Atomic configurations of (a) IrO2 site, (b) Ir-IrO2 site, and (c) Ir-Rh site of Ir@Rhene during the H2O dissociation into OH* and H*, and (d) corresponding water dissociation energy barrier.

Figure S22 .
Figure S22.The optimized configurations of hydroxyl adsorption (OH*) on the (a) Rh site, (b) Ir site, (c) Ir/Rh site, (d) Ir/IrO2 site, and (e) IrO2 site of Ir@Rhene model, showing both the top view and front view of each structure, as well as the corresponding adsorption energy (Eads).

Figure S23 .
Figure S23.The optimized configurations of hydrogen adsorption (H*) on the (a) Rh site, (b) Ir site, (c) Ir/Rh interface site, (d) Ir/IrO2 interface site, and (e) IrO2 site of Ir@Rhene model, showing both the top view and front view of each structure.

Figure S25 .
Figure S25.The optimized configurations of hydrogen adsorption (H*) on the various site along the IrO2 to the Ir/Rh interface.

Table S3 .
Summary of the actual amount of catalyst loading.The Pt, Ir, and Rh contents were determined using ICP-MS analysis.

Table S4 .
Summary of HER properties of the most recent reported high-performance Rhbased catalysts (in 1 M KOH solution).

Table S5 .
Comparison of the HER activity of the as-prepared Ir@Rhene with other state-ofthe-art PGMs-based catalysts reported before (in 1 M KOH solution).