Experimental and Theoretical Insights into Transition-Metal (Mo, Fe) Codoping in a Bifunctional Nickel Phosphide Microsphere Catalyst for Enhanced Overall Water Splitting

Abstract

The facile synthesis of efficient non-precious-metal-based bifunctional catalysts for overall water splitting is highly desirable from both industrial and environmental perspectives. This study reports the electrodeposition and characterization of a transition-metal (Mo, Fe)-codoped nickel phosphide (Ni3P:FeMo) bifunctional catalyst for enhanced overall water splitting in an alkaline medium. The Ni3P:FeMo catalyst exhibited outstanding electrocatalytic performance for both the hydrogen evolution reaction and oxygen evolution reaction with low overpotentials of −103 and 290 mV, respectively, at a high current density of 100 mA/cm2 along with fast electrocatalytic kinetics. A full water-splitting electrolyzer consisting of a bifunctional Ni3P:FeMo catalyst required a low cell voltage of 1.48 V to attain a current density of 10 mA/cm2 with excellent stability for more than 50 h. Density functional theory calculations provided insights into the microscopic mechanism of the effective modulation of the p- and d-band centers of the P and Ni active sites by the Mo and Fe codoping of Ni3P, thereby enhancing the bifunctional catalytic activity of Ni3P.

rGO functionalized (Ni,Fe)-OH for an efficient trifunctional catalyst in low-cost hydrogen generation via urea decomposition as a proxy anodic reaction

“…This can be achieved by developing electrocatalysts derived particularly from the earth-abundant materials that work for both cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) with high catalytic activity and durability under operational conditions in harsh alkaline (pH ∼ 14) or acidic ( pH ∼ 0) electrolytes. A diverse variety of HER and OER catalysts derived from earth-abundant metalbased materials, such as oxide/hydroxide, [19][20][21][22][23][24] sulfide, [25][26][27][28][29][30] telluride, [31][32][33] selenide, 34,35 phosphide, 36 carbide, 37 nitride, 38 and metal-organic frameworks [39][40][41] have been explored. However, the majority of the works have demonstrated catalysis selectively only for HER or OER, while bifunctional catalytic activity for overall water-splitting is desired.…”

Electronic structure engineering for electrochemical water oxidation

“…So far, the state-of-the-art IrO 2 and RuO 2 exhibit the best catalytic OER activity, but their low terrestrial availability and high cost limit their use in large scale applications. [22][23][24] Therefore, signicant research has been directed toward developing earth-abundant transition-metal-based electrocatalysts including oxides, layered double hydroxides (LDH), nitrides, suldes, selenides, and perovskite-based materials. [25][26][27][28][29][30][31][32][33][34] The transition-metal-based catalysts proved to have lower cost, higher natural abundance, unique electronic and mechanical properties, and good OER performances.…”

Designing and Tuning the Electronic Structure of Nickel–Vanadium Layered Double Hydroxides for Highly Efficient Oxygen Evolution Electrocatalysis

“…Hence, we reasonably considered the O sites to be the OER active sites and systematically explored the HDE values of all possible O binding sites (O NNN , O FNN , O FFN , and O FFF , where subscripts N = Ni and F = Fe) to ascertain favorable open O sites for oxide binding. The calculated HDE values in Figure S2 (Supporting Information) reveal that the Ni 0.75 Fe 0.25 LDH structure has the lowest HDE value except Fe­(OH) 2 , which is structurally unstable due to severe hydrogen (H) shedding. , Furthermore, only this atomic configuration can lead to well-dispersed V atoms that efficiently reduce the number of O NNN sites while maintaining the highest HDE (Supporting Information Figure S2). From these observations, one can envisage that the Ni 0.75 Fe 0.25 LDH structure would be more catalytically active because the active formation of open O sites plays a vital role in facilitating the initiation of the OER process.…”

“…Density functional theory (DFT) calculations enable the practical design of complex catalytic materials, including multimetal hydroxides, via a comprehensive understanding of the mechanism of water oxidation at the atomic level, as well as key performance factors. − However, significant efforts and advances have been made to elucidate the high OER activity of state-of-the-art multimetal oxides and hydroxides, particularly in the calculation of the electronic structures and electrocatalytic mechanism. It should be noted that the theoretical effects of both the metal composition and changes in the ratio on oxygen-evolving activity have not been tested with experimental data.…”