Operando Unraveling of the Structural and Chemical Stability of P-Substituted CoSe₂ Electrocatalysts toward Hydrogen and Oxygen Evolution Reactions in Alkaline Electrolyte

Abstract

The question of whether the metal chalcogenides (phosphides) that have been acknowledged to be efficient materials for bifunctional electrocatalysts really perform as the active species or just “pre-catalysts” has been debated. Herein, a series of operando measurements, including in situ X-ray absorption spectroscopy, liquid-phase transmission electron microscopy, and in situ Raman spectroscopy, were conducted to unravel in real time the structural and chemical stability of P-substituted CoSe2 electrocatalysts under both hydrogen and oxygen evolution reactions (HER and OER, respectively) in an alkaline electrolyte. It can be conclusively revealed that, in an alkaline electrolyte, the P-substituted CoSe2 electrocatalyst was acting as the “pre-catalyst” rather than the real reactive species. The introduction of phosphorus is speculated to generate more vacancies or defects around Co cations in the initial CoSe2 and considerably facilitates the structural transformation into the “real reactive species”, such as metallic cobalt (for HER) and cobalt oxyhydroxide (for OER).

Recent advances in transition metal-based electrocatalysts for alkaline hydrogen evolution

“…Interestingly, the role of P in the Psubstituted CoSe 2 is quite different. 68 Zhu et al suggested that the presence of P could generate more vacancies/defects in the CoSe 2 and significantly benefited the structural transformation into metallic cobalt which is the intrinsic catalytic species for HER.…”

In Situ Electrochemical Oxidation of Cu2S into CuO Nanowires as a Durable and Efficient Electrocatalyst for Oxygen Evolution Reaction

“…2,6,[29][30][31] While this instability has been ignored in most studies, when analyzed in detail, the excellent performances obtained for chalcogenides and pnictides have in some cases been related not to the chalcogenide or pnictide cations, but to the in situ formed oxide or (oxy)hydroxide. [32][33][34][35][36][37][38][39] For example, the OER activity of CoSx, 40 NiS, 27 NiSe, 6 and NixFe1-xSe2 41 catalysts was demonstrated to be related to the partial or complete oxidization of the chalcogenide to the corresponding oxide/(oxy)hydroxide.…”

ZnO‐Templated Selenized and Phosphorized Cobalt‐Nickel Oxide Microcubes as Rapid Alkaline Water Oxidation Electrocatalysts

“…After activation,t he sample outstripped RuO 2 multifacetedly,w ith the same overpotential at 10 mA cm À2 (308 mV) and smaller Ta fel slope (40 mV dec À1 )a se xhibited in Figure 4a and c. The transformation from phosphides to hydroxides in the OER has been provedb yi ns itu characterization. [28] We have done post characterization of our catalyst both for the phosphide and selenide samples. The catalysts after the chronopotentiometry tests were wiped off from the electrode surface and were characterizedt hrough Ramanspectrometry Figure S6 (in the Supporting Information).…”

“…These results revealt he unique contribution of the core-shell structure to the catalytic performance, where the high-index TMO core acts as the active sites [12] and the amorphous phosphide shell acts as the pre-catalyst. [28] Moreover,t he two phases show as ynergic effect through more active sites and assisted electron migration at the interface. [4d, 43]…”

“…[6a, 25] Partially phosphorized cobalt oxide has been studied for HER and OER electrocatalysis. [26] Wu et al [27] investigated nickel-cobalt phosphide for water splitting at neutralp H. To achieve ab ifunctional catalytic performance in alkaline solution, Zhu et al [28] fabricated P-substituted CoSe 2 nanoparticles with improved performance and stability.S till, the nano-size and low packing density would discourage the commercial application. The next aim is to maintain the performance of the catalysts on the microscale through the combinationoft he two tactics.…”