Effect of Atomic Ordering Transformation of PtNi Nanoparticles on Alkaline Hydrogen Evolution: Unexpected Superior Activity of the Disordered Phase

Abstract

Compared to the acidic hydrogen evolution reaction (HER), the sluggish reaction rate in an alkaline electrolyte makes it a priority to develop highly efficient and cost-effective catalysts. Incorporation of Pt with transition metals to form alloy nanocrystals with different structures and atomic distributions has been reported as a promising approach to enhance HER activity and improve Pt utilization. However, whether the structural ordering of the Pt-based bimetallic alloy affects the HER activity still remains unknown. Here, we synthesized PtNi/C nanoparticles through a modified coprecipitation method and obtained their ordered and disordered phases at different annealing temperatures in a reducing atmosphere. It is contrary to our expectation that the disordered PtNi/C exhibited a superior activity toward the HER in alkaline media compared with the ordered PtNi/C. To understand this interesting phenomenon, a systematic study combining X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) was conducted. In addition, we studied the mechanism of the HER in an alkaline electrolyte based on newly constructed models. The density functional theory (DFT) calculation demonstrated that the unexpected activity change may be attributed to the synergistic effect between the formation of Ni/Pt–OH bonds and the increased degree of disorder of Pt and Ni atoms on their surface.

Perspective on intermetallics towards efficient electrocatalytic water-splitting

“…Upon alloying, the d-orbitals interact and the catalyst becomes more active for HER when the d -band vacancies are introduced and becomes less active as d-band vacancies are filled. 91 Similar observations have also been made for PtNi, LaNi 5 , TiNi 3 , ZrNi 3 , HfPd 3 , MoPt 3 , FeR (R = rare earth metals), and Ni-Mo-NGTs 89,104,138,176,222 In the case of NiIrRuAl, the charge transfer induced Ni gave rise to modified surface valence states that optimized the H + adsorption and improved the catalytic HER activity. 164 Pt 2 Si showed higher catalytic HER activity than Pt, by facilitating HO-H bond breaking and H + adsorption through the incorporated Si and remained unchanged in the catalytic process.…”

“…137 Likewise, PtNi/C was prepared in the same fashion but at a much lower temperature. 138 The group of Li used N-doped graphite nanotubes as a highly active substrate for their intermetallic Ni-Mo nanocatalysts, (Figure 3d). First, the Ni-N-Doped graphite nanotubes were prepared by pyrolysis followed by acid etching, and then the Ndoped graphite tubes with residue Ni (Ni-NGTs) were impregnated in an aqueous ammonium molybdate solution.…”

H2 In Situ Inducing Strategy on Pt Surface Segregation Over Low Pt Doped PtNi5 Nanoalloy with Superhigh Alkaline HER Activity

“…In this part, the alkaline‐HER activity of PtNi 5 ‐ n ( n = 0, 0.3, and 0.5 MPa) and commercial Pt/C were simulated by DFT based on the constructed models of PtNi 5 ‐18% (Figure S6a, Supporting Information), 38%, 50% (Figure 7a) and Pt(111) (Figure S6b, Supporting Information). According to the literature reports, [ 32 ] the real reaction route can be justified by the Tafel slope. For the scenario of present work, the reaction would prefer to follow the Volmer–Tafel mechanism due to the low Tafel slopes (<30 mV dec −1 , Figure 5e).…”

Self‐confined CoPt/Mo2C nanoparticles encapsulated in carbon cages for boosted hydrogen evolution catalysis

“…At the overpotential of 0.1 V, HER current density catalyzed by CoPt‐Mo 2 C@C‐1 can reach 6.6 A mg Pt ‐1 , which is 12 times higher than that of the Pt/C catalyst. This Pt utilization toward alkaline HER catalysis is among the best of the reported Pt based composited catalysts [ 28,40–46 ] (Figure 6B).…”