Metal–Organic-Framework-Derived Hollow CoS_x@MoS₂ Microcubes as Superior Bifunctional Electrocatalysts for Hydrogen Evolution and Oxygen Evolution Reactions

Abstract

Electrocatalytic water-splitting catalysts play important roles in clean energy conversion systems. Herein, metal–organic framework-derived (MOF-derived) hollow CoS x @MoS2 microcubes were successfully synthesized by a novel method. Co-MOF [(CH3)2NH2]­[Co­(HCOO)3] prepared by a simple liquid precipitation method at room temperature reacted with S2– released from thioacetamide (TAA) to generate Co9S8 under solvothermal conditions. Through hydrothermal treatment, numerous MoS2 nanosheets grew on the surface of CoS x vertically and uniformly after introduction of sulfur and molybdenum sources, finally generating CoS x @MoS2 heterostructures. As bifunctional electrocatalysts, the heterostructures exhibited remarkable performance for the hydrogen evolution reaction with a low overpotential of 239 mV when the current density increased up to 10 mA cm–2 and a small Tafel slope of 103 mV dec–1 in 0.5 M H2SO4. They also worked effectively for the oxygen evolution reaction with a low overpotential of 347 mV at 10 mA cm–2 in 1 M KOH. The enhanced electrocatalytic activities of CoS x @MoS2 can be ascribed to their unique heterostructures and the synergism between CoS x and MoS2.

Boosting Hydrogen Evolution on MoS2/CNT Modified by Poly(sodium‐p–styrene sulfonate) via Proton Concentration in Acid Solution

“…The S 2p spectrum shown in Figure 4A had two characteristic peaks at 160.4 eV and 161.6 eV, corresponding to S 2p 3/2 and 2p 1/2 [46] . The four peaks at 224.9 eV, 227.5 eV and 230.7 eV in Figure 4B could be ascribed to Mo−S, Mo 3d 5/2 and 3d 3/2 , respectively [47] . The presence of Mo 6+ in the spectrum could be contributed to the oxidation of the surface [48] .…”

“…[46] The four peaks at 224.9 eV, 227.5 eV and 230.7 eV in Figure 4B could be ascribed to MoÀ S, Mo 3d 5/2 and 3d 3/2 , respectively. [47] The presence of Mo 6 + in the spectrum could be contributed to the oxidation of the surface. [48] The spectra of Mo 3d and S 2p both exhibited negative shifts after MoS 2 /CNT treated by PSS, indicating the increase of electron density around the surface of the PSS-MoS 2 /CNT.…”

Metal–Organic‐Framework‐Derived Nanostructures as Multifaceted Electrodes in Metal–Sulfur Batteries

“…Additionally, the cooperative effect on the interphases between diverse metal compounds can modify the electronic structures of catalytic sites for adsorbing and activating the reactant molecules and optimize the configurations and reaction pathways of the generated intermediates, thus resulting in significantly improved reaction dynamics and rates. [ 266–268 ] In this light, Zou and co‐workers presented a unique hollow structure that enabled uniformly distributed CoP nanoparticles on TiO x to form hybrid CoP/TiO x heterostructure (Figure 17c–e). [ 269 ] Significantly, the heterostructured CoP–TiO x hybrid material could achieve the electron reapportionment on the CoP/TiO x interfaces and optimize the electric density of CoP, which eventually results in accelerated OER dynamics.…”

Metal‐Organic Framework Derived Nanostructured Bifunctional Electrocatalysts for Water Splitting

“…In a two-step typical solvothermal-hydrothermal approach, Yang et al synthesized nanostructured hollow CoS x @MoS 2 microcubes using a cube-shaped CoÀ MOF, [(CH 3 ) 2 NH 2 ][Co(HCOO) 3 ]. [150] Briefly, CoÀ MOF reacted with thioacetamide molecules solvothermally at 120 °C using ethanol as solvent and produced hollow Co 9 S 8 microcubes, which further treated hydrothermally with aqueous solution of Na 2 MoO 4 • 2H 2 O and thiourea at 200 °C to produce hollow CoS x @MoS 2 microcubes. Basically, in second step MoS 2 nanosheets were grown on the surface of Co 9 S 8 .…”