Deciphering the Influence of Morphology and Crystal Structure on Alkaline Hydrogen Evolution Activity in Polymorphic Cobalt Diselenide

Abstract

Polymorphic cobalt diselenide (CoSe 2 ) has emerged as a highly promising catalyst for the alkaline hydrogen evolution reaction (HER) due to its favorable electrocatalytic activity and stability. Previous studies have emphasized the unique advantages of different crystal structures (orthorhombic and cubic) of CoSe 2 in the HER. This prompted us to investigate whether the HER catalytic activity of polymorphic CoSe 2 phases is contingent on their crystal structure and morphology. Specifically, we fabricated two distinct phases of CoSe 2 , namely, orthorhombic and cubic, each characterized by unique morphologies on carbon cloth (CC) and referred to as o-CoSe 2 /CC and c-CoSe 2 /CC. The o-CoSe 2 /CC exhibits Cadamba-like flower structures, while c-CoSe 2 /CC has a densely packed and vertically aligned nanoneedlelike morphology. Interestingly, our findings indicate that both catalysts demonstrated analogous HER performance under identical reaction conditions. For instance, o-CoSe 2 /CC achieved an overpotential of 178 ± 3 mV (@10 mA cm −2 ) with a Tafel slope of 111 ± 5 mV dec −1 , closely mirroring the performance of c-CoSe 2 /CC (187 ± 4 mV, 112.8 ± 3 mV dec −1 ). This equivalence in the performance can be attributed to several factors, including their similar electrochemically active surface areas, equivalent numbers of active sites, comparable reaction kinetics, and analogous charge-transfer rates. This research work decisively demonstrates that in polymorphic materials, structural variations and morphological differences may have minimal influence on dictating the HER activity, while the number and kind of active sites are the dominant factors in regulating the HER activity.

Facile Deposition of a Spherical Ruthenium–Cobalt Alloy on Nickel Foam as a High-Performance Electrocatalyst for Alkaline Hydrogen Production

“…The catalysis of water into hydrogen and oxygen begins with the adsorption of hydrogen on the surface of advanced catalysts, forming metal–hydrogen (M–H) bonds . Although Pt can form Pt–H bonds and achieve impressive HER catalysis performance, its high cost and limited availability make it unsuitable for large-scale applications. , Consequently, research has focused on exploring economical, efficient, and robust alternatives to Pt-based electrocatalysts for alkaline media, − with recent attention directed toward Ru-based electrocatalysts owing to their ability to form Ru–H bonds similar to Pt catalysts. , Ru is more cost-effective, corrosion-resistant, and possesses a high intrinsic catalytic value. , A recent study has shown that uniformly dispersed Ru nanoparticles on graphite supports exhibit better HER activity than benchmark Pt/C. , However, the strong affinity of Ru to hydrogen atoms poses a challenge, prompting an investigation into alloying Ru with 3d transition metals (TM = Co, Ni, and Cu) as a potential solution. , For instance, alloying Ru with Cu enhances the strength of Cu–H interactions while weakening Ru–H interactions, thereby improving the overall HER efficiency . Furthermore, alloying Ru with earth-abundant TMs can effectively reduce the amount of the Ru metal required by up to an order of magnitude, enabling the synthesis of cost-competitive and more efficient electrocatalysts suitable for large-scale applications. , Previous studies have demonstrated that bimetallic synergy between noble metals and TMs enhances electrocatalytic activities, suggesting that varying the compositions of such alloys is an effective method to optimize the utilization efficiency of Ru in practical applications. , …”