Nickel Hydroxide‐Supported Ru Single Atoms and Pd Nanoclusters for Enhanced Electrocatalytic Hydrogen Evolution and Ethanol Oxidation

Abstract

The rational fabrication of Pt‐free catalysts for driving the development of practical applications in alkaline water electrolysis and fuel cells is promising but challenging. Herein, a promising approach is outlined for the rational design of multimetallic catalysts comprising multiple active sites including Pd nanoclusters and Ru single atoms anchored at the defective sites of Ni(OH)2 to simultaneously enhance hydrogen evolution reactions (HER) and ethanol oxidation reactions (EOR). Remarkably, Pd12Ru3/Ni(OH)2/C exhibits a remarkably reduced HER overpotential (16.1 mV@10 mA cm−2 with a Tafel slope of 21.8 mV dec−1) as compared to commercial 20 wt.% Pt/C (26.0 mV@10 mA cm−2, 32.5 mV dec−1). More importantly, Pd12Ru3/Ni(OH)2/C possesses a self‐optimized overpotential to 12.5 mV@10 mA cm−2 after 20 000 cycles stability test while a significantly decreased performance for commercial 20wt.% Pt/C (64.5 mV@10 mA cm−2 after 5000 cycles). The mass activity of Pd12Ru3/Ni(OH)2/C for the EOR is up to 3.724 A mgPdRu−1, ≈20 times higher than that of commercial Pd/C. Electrochemical in situ Fourier transform infrared measurements confirm the enhanced CO2 selectivity of Pd12Ru3/Ni(OH)2/C while synergistic and electronic effects of adjacent Ru, Pd, and OHad adsorption on Ni(OH)2 at low potential play a key role during EOR.

Effective electronic tuning of Pt single atomsviaheterogeneous atomic coordination of (Co,Ni)(OH)2for efficient hydrogen evolution

“…The comparative observation confirms that the first step for the decomposition of water (the H–OH bond breaking) takes place on the surface of the (Co,Ni)(OH) 2 rather than due to the effect of lattice oxygen (Fig. 5b) 68,72 The water molecules adsorb on hydrophilic (Co,Ni)(OH) 2 and dissociate to generate highly active M–*OH intermediates. After the H–OH bond breaks, the formation of Ni–*OH and Co–*OH intermediates would further expedite the water splitting and induce *H transfer to the single-atom Pt sites to generate Pt–*H. The second step for the decomposition of water is the formation of H 2 , which is accessible by the interosculation of adjacent Pt–*H species (Tafel step).…”

“…Furthermore, an appropriate and widely used frequency range of low (0.01 Hz) to high (100 K Hz) frequency was applied for the HER impedance measurements in this study. 67,68 Pt 1 /(Co,Ni)(OH) 2 /C demonstrated the smallest charge transfer resistance, which proves the optimized electronic transfer and enhanced intrinsic activity for the HER (Fig. S7 and S8, ESI †).…”

“…32,65,66 The "fluctuation behavior" of the LSV was due to relatively large streams of bubbles being generated at the very large current density, which regularly interrupt the mass transfer process, leading to the evident fluctuation of the polarization curve. Furthermore, an appropriate and widely used frequency range of low (0.01 Hz) to high (100 K Hz) frequency was applied for the HER impedance measurements in this study 67,68 . Pt 1 /(Co,Ni)(OH) 2 /C demonstrated the smallest charge transfer resistance, which proves the optimized electronic transfer and enhanced intrinsic activity for the HER (Fig.…”

“…S16). It suggests that the synergistic interaction of highly dispersed Pt anchoring on (Co,Ni)(OH) 2 nanoparticles and the synergistic effect of Pt Please do not adjust margins Please do not adjust margins 5a) 68,72 . Unfortunately, it is hard to distinguish M-OH and M-O vibrations due to the overlapping of the bands.…”

“…The presence of lattice oxygen was very weak in Pt 5d). 68,72 Please do not adjust margins Please do not adjust margins 111), which is the rate-limiting step. According to previous reports, the catalysts combining Pt and hydroxides show better HER performance than pure Pt in alkaline media.…”