Hierarchical Nanoassembly of MoS₂/Co₉S₈/Ni₃S₂/Ni as a Highly Efficient Electrocatalyst for Overall Water Splitting in a Wide pH Range

Abstract

The design of low-cost yet high-efficiency electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) over a wide pH range is highly challenging. We now report a hierarchical co-assembly of interacting MoS 2 and Co 9 S 8 nanosheets attached on Ni 3 S 2 nanorod arrays which are supported on nickel foam (NF). This tiered structure endows high performance toward HER and OER over a very broad pH range. By adjusting the molar ratio of the Co:Mo precursors, we have created CoMoNiS-NF-xy composites (x:y means Co:Mo molar ratios ranging from 5:1 to 1:3) with controllable morphology and composition. The three-dimensional composites have an abundance of active sites capable of universal pH catalytic HER and OER activity. The CoMoNiS-NF-31 demonstrates the best electrocatalytic activity, giving ultralow overpotentials (113, 103, and 117 mV for HER and 166, 228, and 405 mV for OER) to achieve a current density of 10 mA cm −2 in alkaline, acidic, and neutral electrolytes, respectively. It also shows a remarkable balance between electrocatalytic activity and stability. Based on the distinguished catalytic performance of CoMoNiS-NF-31 toward HER and OER, we demonstrate a two-electrode electrolyzer performing water electrolysis over a wide pH range, with low cell voltages of 1.54, 1.45, and 1.80 V at 10 mA cm −2 in alkaline, acidic, and neutral media, respectively. First-principles calculations suggest that the high OER activity arises from electron transfer from Co 9 S 8 to MoS 2 at the interface, which alters the binding energies of adsorbed species and decreases overpotentials. Our results demonstrate that hierarchical metal sulfides can serve as highly efficient all-pH (pH = 0−14) electrocatalysts for overall water splitting.

Atomically Dispersed Mo Supported on Metallic Co9S8 Nanoflakes as an Advanced Noble‐Metal‐Free Bifunctional Water Splitting Catalyst Working in Universal pH Conditions

“…However, no significant changes are detected under neutral and alkaline condition. [12,27] Furthermore, the results of fresh sample and after 24 h OER in acid for the Mo-Co 9 S 8 @C also show that a small amount of molybdenum trioxides are existence, among three weak peaks at 338, 363, and 486 cm −1 are corresponding to the feature of MoO 3 .…”

“…Furthermore, the current−time curve (insets of Figure 3c) also indicates that Mo-Co 9 S 8 @C reserves similar catalytic performance for at least 24 h in 0.5 m H 2 SO 4 . [7,12,24] Such superior electrocatalytic activity of Mo-Co 9 S 8 @C might be attributed to the following merits: 1) the synergetic interactions between high oxidation state Co and single-atomic Mo species to form insoluble compounds under acidic conditions, which benefits the OER and overall water splitting in different pH conditions; 2) our working electrode is directly in situ grown on the carbon cloth, which also contributes to the enhancement of long-time stability. Energy Mater.…”

“…Only a few non-noble metal catalysts (such as Co 3 O 4 , MnO x , Co-POMs, NiFeP, N-doped WC, MoSe 2 NS/MoO 2 NB/CNT-M, and Co-doped MoS 2 ) have been reported that functionalized in an acidic media. [12] Very recently, isolated nonprecious metal atoms that are dispersed on specific functional supports [13] have attracted tremendous interests. [1a,7,10c,e, f,11] Furthermore, from the viewpoint of the practical application, the development of one electrocatalyst with universal HER and OER activities in the same electrolyte is undoubtedly technologically important and urgently demanded.…”

A Minireview on Nickel‐Based Heterogeneous Electrocatalysts for Water Splitting

“…For multimetal-doped Ni chalcogenides, recently, amazingly, Kanatzidis group synthesized a hierarchical MoS 2 and Co 9 S 8 nanosheets anchored on Ni 3 S 2 nanorods (MoS 2 /Co 9 S 8 /Ni 3 S 2 /Ni) only via the one-step hydrothermal method by adjusting molar ratio of the Co: Mo precursors ( Figure 4c). [39] Gibbs free energies of four electrochemical reaction steps for OER (2H 2 O!O 2 + 4H + + 4e À ) on the Co 9 S 8 surfaces of Co 9 S 8 (100)/MoS 2 structures were estimated using calculated O*, OH*, and OOH* intermediates on different surface sites (Figure 4d-f). It could be seen that formation of OÀ O bond in OOH* is the rate-limiting step in pure Co 9 S 8 , while the rate limiting step was changed to initial OH* adsorption in Co 9 S 8 /MoS 2 (d) formed with MoS 2 layers parallel to the Co 9 S 8 (100) surface.…”

Reversible ternary nickel‐cobalt‐iron catalysts for intermittent water electrolysis

“…The combination of Ni and Co also leads to a substantial enhancement in the catalytic activity of HER. 30,31 However, a ternary nickel-cobalt-iron catalyst that is active and stable for reversible OER and HER has been rarely studied. Furthermore, the interdependence of the electrochemical performances of these multimetallic catalysts upon the compositions is yet to be understood and remains an intriguing area to explore.…”