Electrocatalytic Performance and Stability of Nanostructured Fe–Ni Pyrite-Type Diphosphide Catalyst Supported on Carbon Paper

Abstract

A simple and effective method to prepare an active and stable nanostructured working electrode for electrochemical water splitting is described. Specifically, mixed Fe-Ni diphosphide was prepared by sputtering a 200-nm-thick layer of Permalloy onto carbon paper gas diffusion layer followed by gas transport phosphorization reaction. The mass density of the resultant diphosphide phase was established to be 1.1 mg/cm 2. Energy-dispersive X-ray microanalysis shows that the actual elemental composition of the resultant ternary electrocatalyst is approximately Fe 0.2 Ni 0.8 P 2 , while the powder X-ray diffraction analysis confirms that the electrocatalyst crystallizes in NiP 2 cubic pyrite-like structure. As a cathode for hydrogen evolution reaction (HER) in acidic and alkaline electrolytes, this earth-abundant electrode has exchange current densities of 6.8410 3 and 3.1610 3 mA/cm 2 and Tafel slopes of 55.3 and 72.2 mV/dec, respectively. As an anode for oxygen evolution reaction (OER) in alkaline electrolyte, the electrode shows an exchange current density of 2.8810 4 mA/cm 2 and Tafel slope of 49.3 mV/dec. The observed high activity of the electrode correlates well with its electronic structure, which was assessed by density functional theory (DFT) calculations. The stability of Fe 0.2 Ni 0.8 P 2 electrocatalyst in HER and OER was evaluated by means of accelerated degradation test and chronopotentiometry. The results of these experiments elucidate partial dissolution and entire chemical transformation of Fe 0.2 Ni 0.8 P 2 as the main mechanisms of the electrode degradation during HER and OER, respectively. Overall, our findings could facilitate the composition-based design of active, stable, and durable phosphide electrodes for electrochemical water splitting.

Emerging nanostructured electrode materials for water electrolysis and rechargeable beyond Li-ion batteries

“…The as-prepared nanostructured Fe−Ni pyrite-type diphosphide shows excellent electrocatalytic performance towards HER. The observed high activity of the electrode correlates well with its electronic structure predicted by DFT calculations [35].…”

“…On the other hand, expansive strain produces the opposite effect [34]. Hence, a theoretical design of the optimal supported surface is possible, and in principle, the strength of the adsorption can be tuned by engineering ad hoc the surface structure [19,28,30,32,[35][36][37][38].…”

Structure–Activity Relationships for Pt‐Free Metal Phosphide Hydrogen Evolution Electrocatalysts

“…The resultant cathode exhibits excellent performance towards HER, showing T S =79 mV dec −1 and η 10 =120 mV, as well as good long‐term stability for at least 72 h while driving a cathodic current density of −10 mA cm −2 . This simple direct phosphorization method is versatile and later on was extended to give the otherwise challenging nanostructured Al‐doped nickel phosphides and mixed Fe−Ni diphosphide cathodes . CoP nanowires were prepared by a similar phosphorization method using Co metal foam .…”

“…[74] This simple direct phosphorization method is versatile and later on was extended to give the otherwise challenging nanostructured Al-doped nickel phosphides and mixed FeÀNi diphosphide cathodes. [75,76] CoP nanowires were prepared by as imilar phosphorization method using Co metal foam. [77] Metal foam was also used as ap recursor to hydrothermally grow Ni/Co hydroxide nanowires which were subsequently converted into Co 1.5 Ni 0.5 Pn anowires supported on Ni foam by the direct phosphorization using red P. [78] Mixing of two or more metals to tune the catalytic properties has been widely explored, while the reports on the non-metal sublattice substitutions are lessc ommon.…”

Stability of CoPx Electrocatalysts in Continuous and Interrupted Acidic Electrolysis of Water

“…CA/CP shows the stability under constant and continuous working conditions, while repeated LSV/CV demonstrates the stability under dynamic power supply. The latter is especially important when a water splitting device is coupled with renewable (e. g. solar or wind) electricity, which is intermittent in nature . Besides electrochemical methods, compositional analysis of both electrodes (by X‐ray Photoelectron Spectroscopy, XPS) and the electrolytes (Inductively coupled plasma mass spectrometry, ICP‐MS) after the stability tests is also essential to evaluate the stability of electrocatalysts …”