Cobalt Sulfide/Nickel Sulfide Heterostructure Directly Grown on Nickel Foam: An Efficient and Durable Electrocatalyst for Overall Water Splitting Application

Abstract

Fabrication of high-performance noble-metal-free bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water is a promising strategy toward future carbon-neutral economy. Herein, a one-pot hydrothermal synthesis of cobalt sulfide/nickel sulfide heterostructure supported by nickel foam (CoS /NiS@NF) was performed. The Ni foam acted as the three-dimensional conducting substrate as well as the source of nickel for NiS. The formation of CoS /NiS@NF was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. The formation of CoS /NiS@NF facilitated easy charge transport and showed synergistic electrocatalytic effect toward HER, OER, and overall water splitting in alkaline medium. Remarkably, CoS /NiS@NF showed catalytic activity comparable with that of benchmarking electrocatalysts Pt/C and RuO. For CoS /NiS@NF, overpotentials of 204 and 280 mV were required to achieve current densities of 10 and 20 mA cm for HER and OER, respectively, in 1.0 M KOH solution. A two-electrode system was formulated for overall water splitting reaction, which showed current densities of 10 and 50 mA cm at 1.572 and 1.684 V, respectively. The prepared catalyst exhibited excellent durability in HER and OER catalyzing conditions and also in overall water splitting operation. Therefore, CoS /NiS@NF could be a promising noble-metal-free electrocatalyst for overall water splitting application.

Effect of the Solvent Ratio (Ethylene Glycol/Water) on the Preparation of an Iron Sulfide Electrocatalyst and Its Activity towards Overall Water Splitting

“…When Fe pulled the electronic density towards it, the S 2p peak was red‐shifted and vice versa. A less prominent peak located at ∼169 eV in the S 2p spectra of all the materials appeared due to the formation of S with higher oxidation state in solvothermal condition . The VBXPS revealed that as the amount of Fe 3+ in the material decreased, the electron density near Fermi Energy (E F ) increased (see Figure c).…”

“…A less prominent peak located at~169 eV in the S 2p spectra of all the materials appeared due to the formation of S with higher oxidation state in solvothermal condition. [33] The VBXPS revealed that as the amount of Fe 3 + in the material decreased, the electron density near Fermi Energy (E F ) increased (see Figure 3c). As a consequence, the valence band edge gradually shifted towards lower BE value from FS 20 until FS 60 and for FS 80, it shifted to higher BE value.…”

Spinel oxide CoFe2O4 grown on Ni foam as an efficient electrocatalyst for oxygen evolution reaction

“…[1][2][3][4] Due to the OER involving four-proton-coupled electron transfer and O]O band formation, the overpotential of the OER is higher than that of the HER in electrochemical water splitting, and the OER is the bottleneck of electrochemical water splitting. [5][6][7][8][9][10][11] In order to reduce the overpotentials of the OER, efficient electrocatalysts with excellent catalytic activity and stability are needed. Noble metal-based materials like Ru-and/or Ir-based catalysts have been well-known as prominent catalysts for OER, but Ru-and/or Ir-based catalysts still require larger overpotential to deliver a current density of 10 mA cm À2 .…”

Hierarchical Cobalt Sulfide/Molybdenum Sulfide Heterostructure as Bifunctional Electrocatalyst towards Overall Water Splitting

“…Inspection of the Mo 4p spectra of C 2 M 1 S exhibited the shifting of B. E. towards higher region as compared to MoS 2 (see Figure b). All these Blue‐shifts in XPS spectra confirmed strong electronic coupling and charge redistribution between CoS x and MoS 2 via formation of nano‐interfaces which facilitated faster charge transfer . The presence of S 2p 1/2 and S 2p 3/2 peaks in the deconvoluted S 2p spectra (Figure d) confirmed the formation of Mo−S and Co−S bonds in C 2 M 1 S .…”