Efficient Mo–Co(OH)2/Co3O4/Ni foam electrocatalyst for overall water splitting

Abstract

Bifunctional catalysts for water splitting based on 3d transition metals are well-documented. Herein, a Co3O4 layer was introduced between tremella-like Mo–Co(OH)2 and nickel foam through electrodeposition(1st)-pyrolysis-electrodeposition(2nd) strategy as the conductive secondary substate. The secondary electrodeposition particularly led to introduce the Mo species into the surface layer of Co(OH)2. The as-prepared Mo–Co(OH)2/Co3O4/NF-x(x represents the deposition time) was further applied as the catalyst for HER, OER and the overall water-splitting reactions. Notably, the Mo–Co(OH)2/Co3O4/NF-800 catalyst exhibited outstanding activity to achieve a current density of 10 ​mA ​cm-2, with overpotentials of 116 ​mV and 234 ​mV for HER and OER in 1 ​M KOH, respectively. Moreover, a cell voltage of 1.62V was only required to achieve the current density of 10 ​mA ​cm-2, when the catalyst was assembled as the anode and cathode simultaneously. Several characterizations were performed, including HRTEM, XRD, SEM and XPS analysis, to explore the structure-activity relationship of the Mo–Co(OH)2/Co3O4/NF catalyst. Notably, the existence of the Co3O4 nanosheet middle layer enhanced the electro-chemical active surface area of the whole Mo–Co(OH)2/Co3O4/NF catalyst, which boosted the conductivity of the catalyst. Moreover, the XPS analysis revealed that the doped Mo6+ can attract the electrons from Co2+, increasing the active sites that are favorable for the OER and HER. The unique synthetic strategy adapted in this work will open up a new approach for the construction of heteroatom-doped multilayered heterostructure to achieve effective catalytic activity for overall water-splitting.