Co/Co9S8@S,N-doped porous graphene sheets derived from S, N dual organic ligands assembled Co-MOFs as superior electrocatalysts for full water splitting in alkaline media

Abstract

Here we report the synthesis of Co/Co9S8 core-shell structures anchored onto S, N co-doped porous graphene sheets (Co/Co9S8@SNGS) from thiophene-2,5-dicarboxylate (Tdc) and 4,4ˊ-bipyridine (Bpy) dual organic ligands assembled Co-based metal-organic frameworks (Co-MOFs) in situ grown on graphene oxide sheets (Co-MOFs@GO) by a room-temperature solution reaction. S-containing Tdc and N-containing Bpy not only trigger the growth of Co-MOFs nanocrystals with a fixed S/N atomic ratio of 1:2.4 on GO sheets in the presence of Co2+ in H2O/NaOH system, but also provide S, N doping sources in the pyrolysis process of Co-MOFs to form Co/Co9S8 core-shell structure and S, N co-doping in graphene. The results demonstrate that the obtained Co/Co9S8@SNGS at 1000°C (Co/Co9S8@SNGS-1000) by pyrolysis of Co-MOFs@GO exhibits superiorly bifunctional catalytic activities of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in 0.1M KOH electrolyte, affording an overpotential of 290mV for OER at a current density of 10mAcm−2 and 350mV for HER at a current density of 20mAcm−2. The OER activity of Co/Co9S8@SNGS-1000 is slightly better than that of commercial RuO2 catalyst, simultaneously, Co/Co9S8@SNGS-1000 also exhibits good HER activity. As electrode material for full water splitting in 0.1M KOH solution, the Co/Co9S8@SNGS-1000 electrodes exhibit O2 and H2 generation efficiencies of 2.48 and 4.87μmolmin−1 respectively, at an applied potential of 1.58V (vs. RHE) under the given time range, affording nearly 100% Faradaic yield during electrocatalytic water splitting to produce O2 and H2.