Climbing the Volcano of Electrocatalytic Activity while Avoiding Catalyst Corrosion: Ni₃P, a Hydrogen Evolution Electrocatalyst Stable in Both Acid and Alkali

Abstract

We report microcrystalline Ni3P as a noble-metal-free electrocatalyst for the H2 evolution reaction (HER) with high activity just below those of Ni5P4 and Pt, the two most efficient HER catalysts known. Ni3P has previously been dismissed for the HER, owing to its anticipated corrosion and its low activity when formed as an impurity in amorphous alloys. We observe higher activity of single-phase Ni3P crystallites than for other nickel phosphides (except Ni5P4) in acid, high corrosion tolerance in acid, and zero corrosion in alkali. We compare its electrocatalytic performance, corrosion stability, and intrinsic turnover rate to those of different transition-metal phosphides. Electrochemical studies reveal that poisoning of surface Ni sites does not block the HER, indicating P as the active site. Using density functional theory (DFT), we analyze the thermodynamic stability of Ni3P and compare it to experiments. DFT calculations predict that surface reconstruction of Ni3P (001) strongly favors P enrichment of the Ni4P4 termination and that the H adsorption energy depends strongly on the surface reconstruction, thus revealing a potential synthetic lever for tuning HER catalytic activity. A particular P-enriched reconstructed surface on Ni3P­(001) is predicted to be the most stable surface termination at intermediate P content, as well as providing the most active surface site at low overpotentials. The P adatoms present on this reconstructed surface are more active for HER at low overpotentials in comparison to any of the sites investigated on other terminations of Ni3P­(001), as they possess nearly thermoneutral H adsorption. To our knowledge this is the first time reconstructed surfaces of transition-metal phosphides have been identified as having the most active surface site, with such good agreement with the experimentally observed catalytic current onset and Tafel slope. The active site geometry achieved through reconstruction identified in this work shows great similarity to that reported for Ni2P­(0001) and Ni5P4(0001) facets, serving as a general design principle for the future development of even more active transition-metal phosphide catalysts and further climbing the volcano plot.

Virus-templated Pt–Ni(OH)2 nanonetworks for enhanced electrocatalytic reduction of water

“…The Ni-P alloy deposit was largely amorphous, displaying only a weak, broad peak centered on the (111) facet of fcc nickel (ICDD reference pattern 04-010-6148), similar to previous literature reports for highphosphorus-content, electroless nickel deposits [37]. Additionally, this provides strong evidence against the formation of metal phosphides like Ni3P, which have also shown electrocatalytic HER activity [38]. In contrast, the deposited platinum nanoislands were crystalline in nature, as seen by the appearance of fcc platinum (ICDD reference pattern 04-001-0112) with higher platinum loadings (Figure 3a).…”

Air-stable phosphorus-doped molybdenum nitride for enhanced electrocatalytic hydrogen evolution

“…The referenced commercial Pt/C sample gives the smallest slope of 37 mV/dec, followed by P-Mo-N of 43 mV/dec, Mo-N of 76 mV/dec, and Mo 2 N-r of 71 mV/dec. A slope larger than 30 mV/dec for the P-Mo-N sample suggests a Volmer-Heyrovsky route for HER, 10,11,14 . The exchange current density (j 0 ), the most inherent measure of HER activity, was also calculated based on the Tafel equations (Supplementary Table 2).…”

“…H ydrogen evolution reaction (HER) from electrocatalytic water splitting has been regarded as one of the important strategies to solve the world's increasing energy and environment issues [1][2][3][4][5][6][7][8][9][10] . Water electrolysis requires a stable electrocatalyst which has the ability to overcome high overpotential and provide efficient activity.…”

Nickel Phosphide Electrocatalysts for Hydrogen Evolution Reaction

“…Notably, nickel phosphides have eight mono-phosphides and poly-phosphides with different Ni/P ratios, i.e., Ni3P, Ni5P2, Ni12P5, Ni2P, Ni5P4, NiP, NiP2, and NiP3, and the stoichiometric compositions, crystal phases, and crystal facets show influences on the electrocatalytic HER activity. The nickel phosphides of Ni2P [45], Ni5P4 [46], Ni12P5 [47], Ni3P [48], and NiP2 [49] phases are generally obtained according to the reported results. Pan et al investigated the HER performance of different types of nickel phosphides (Ni12P5, Ni2P, and Ni5P4) and found that their catalytic performance followed the order of Ni5P4>Ni2P>Ni12P5 [50].…”

“…The SEM images in Figure 9c Figure 9f and Tafel plots in Figure 9g clearly show that the HER performance of nickel phosphide nanosheets prepared by S B-U method is better than the one prepared by the S F-B method. Alternatively, Laursen et al prepared Ni 3 P microparticles by a conventional solid-state reaction, which allowed Ni (s) and P (s) to react in an evacuated quartz tube at 700 • C for 24 h [48]. The microcrystalline Ni 3 P as a noble-metal-free electrocatalyst for HER shows high activity lower than those of Ni 5 P 4 and Pt, which are the two most efficient HER catalysts known.…”