Directed synthesis of an unusual uniform trimetallic hydrogen evolution catalyst by a predesigned cobalt-bipy modified bivanadyl capped polymolybdate

Heterometallic sulfides are one type of non-precious metal, environmentally friendly and high-activity electrocatalysts for electrocatalytic hydrogen evolution reaction (HER). Nevertheless, different metallic reagents generally possess distinct nucleation reaction rates. Therefore, there is a still big challenge currently to obtain uniform heterometallic sulfide catalysts especially for trimetallic catalysts. In this work, a new crystalline polyoxometalate (POM)-based coordination polymer [CoIII(bipy)3]2{[CoII(bipy)2(H2O)]2 [HPMoV4MoVI8O40(VIVO)2]}[HPMoV10MoVI2O40(VIVO)2] (abbreviated to Co-bipy-PMo12V2) was prepared, where the bipy is abbreviation of 2,2′-bipy. In the polymer, the POM anions exhibit novel bivanadyl capped Keggin cluster structures and they are further modified cobalt-bipy subunits to form a supramolecular framework. Subsequently, the polymer was used as a “pre-assembled platform” for the preparation of heterometallic sulfides in the presence of thiourea under hydrothermal conditions. Consequently, an unusual high dispersed trimetallic sulfides were in-situ coupled on carbon cloth (CC) substrate to give birth to a novel self-supported CoS2-MoS2-VS2-CC composite electrode. The composite was characterized by PXRD, XPS, SEM, etc. Also, a series of tests on the electrochemical behavior of the composite electrode were carried out using a three-electrode system to investigate its electrocatalytic HER performance. The overpotential and Tafel slope of the electrode can approach to 152 ​mV and 107 ​mV dec−1, respectively. Moreover, the polarization curves of the CoS2-MoS2-VS2-CC electrode completely overlapped before and after 1000 cycles of voltammetric tests in 1.0 ​M KOH electrolyte. The chrono-current method reveals that the CoS2-MoS2-VS2-CC electrode can maintain stability electrocatalytic activity at a current density of 10 ​mA ​cm−2 for at least 24 ​h. Thus, the CoS2-MoS2-VS2-CC catalyst possesses both superior electrocatalytic HER performance and long-term durability. This study provides a facile route for the rational design and preparation of high dispersed trimetallic sulfide catalysts.