Effect of Ion Diffusion in Cobalt Molybdenum Bimetallic Sulfide toward Electrocatalytic Water Splitting

Abstract

The electrocatalyst comprising two different metal atoms is found suitable for overall water splitting in alkaline medium. Hydrothermal synthesis is an extensively used technique for the synthesis of various metal sulfides. Time-dependent diffusion of the constituting ions during hydrothermal synthesis can affect the crystal and electronic structure of the product, which in turn would modulate its electrocatalytic activity. Herein, cobalt molybdenum bimetallic sulfide was prepared via hydrothermal method after varying the duration of reaction. The change in crystal structure, amount of Co−S−Mo moiety, and electronic structure of the synthesized materials were thoroughly investigated using different analytical techniques. These changes modulated the charge transfer at the electrode−electrolyte interface, as evidenced by electrochemical impedance spectroscopy. The Tafel plots for the prepared materials were investigated considering a less explored approach and it was found that different materials facilitated different electrocatalytic pathways. The product obtained after 12 h reaction showed superior catalytic activity in comparison to the products obtained from 4, 8, and 16 h reaction, and it surpassed the overall water splitting activity of the RuO 2 −Pt/C couple. This study demonstrated the ion diffusion within the bimetallic sulfide during hydrothermal synthesis and change in its electrocatalytic activity due to ion diffusion.

Single‐Step Solid‐State Scalable Transformation of Ni‐Based Substrates to High‐Oxidation State Nickel Sulfide Nanoplate Arrays as Exceptional Bifunctional Electrocatalyst for Overall Water Splitting

“…An impressively low cell potential of 1.46 V at 10 mA cm −2 and 1.69 at 100 mA cm −2 , which is indeed noteworthy (CV curve is presented in Figure S18, Supporting Information). To the best of our knowledge, the NIS-450(foam)||NIS-450(foam) electrocatalyst system exhibits the lowest overpotential values reported for the transition metal-based sulfides as a bifunctional electrocatalyst for overall water splitting [16,20,21,23,24,[26][27][28][29][30][31][32][33][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] (Figure 5d). As expected, NIS-450(foam) shows two orders of magnitude higher C dl in comparison to the bare Ni foam (Figure S19, Supporting Information).…”

“…Furthermore, most of the recent works involve the exploitation of multi-metallic or multilayered sulfides, adding further complexity to the already cumbersome synthesis processes. [19,[24][25][26][27][28][29][30][31][32] In spite of tremendous efforts, economically scalable methods for industrial-scale production of morphologically and chemically-engineered earth-abundant binder-free electrocatalysts with low overpotentials for overall water splitting are still missing. Hence, there is an urge to quench the thirst for a bifunctional electrocatalyst, which not only displays low overpotentials but also qualifies the indispensable criterion of a simple and single step, rapid synthesis process at low temperatures (sub-500 °C) for economic scalability to industrial scales.…”

Template free-synthesis of cobalt–iron chalcogenides [Co0.8Fe0.2L2, L = S, Se] and their robust bifunctional electrocatalysis for the water splitting reaction and Cr(vi) reduction

“…There are continuous investigations on the use of active transition elements like Ni, Co, Fe, Cu, and Mo and their combinations with sulphur as electro catalysts. Some varieties include Co–Ni–S, 26–29 Cu–Co–S, and Cu–Mo–S, 30–32 Co–Fe–S, 33–37 Co–Mo–S, 38 and Zn–Co–S. 39 The ternary chalcogenides have shown superior properties like high electrical conductance than monometallic due to the low activation energy for electron transfer between cations.…”

2D Nanosheets of Mo2C/CoMoS4 as Active Electrocatalyst for Water Splitting

“…In recent years, earth‐abundant transition‐metal‐based catalysts gradually emerge as the attractive substitute of noble metal catalysts due to its abundant resources, low cost, and excellent catalytic performance. [ 21–25 ] As a kind of key transition metal catalyst, bimetallic sulfide [ 26–28 ] shows impressively improved catalytic performances benefiting from the synergistic effect [ 29,30 ] of the multiple oxidation states and much richer active sites compared with the single metal sulfide catalyst. [ 31,32 ] As a representative of bimetallic catalyst, Co 2− x Ni x O 2 nanosheets have been successfully used as active and stable electrocatalysts to split water by Li et al [ 33 ] In addition, NiCo 2 S 4 /N,S codoped reduced graphene oxide is reported to efficiently catalyze the water splitting reaction with high stability.…”