Effect of multi-interface electron transfer on water splitting and an innovative electrolytic cell for synergistic hydrogen production and degradation

The cleaning and utilization of industry wastewater are still a big challenge. In this work, we mainly investigate the effect of electron transfer among multi-interfaces on water electrolysis reaction. Typically, the CoS2, Co3S4/CoS2 (designated as CS4-2) and Co3S4/Co9S8/CoS2 (designated as CS4-8-2) samples are prepared on a large scale by one-step molten salt method. It is found that because of the different work functions (designated as WF; WF(Co3S4) = 4.48eV, WF(CoS2) = 4.41eV, WF(Co9S8) = 4.18 eV), the effective heterojunctions at the multi-interfaces of CS4-8-2 sample, which obviously improve interface charge transfer. Thus, the CS4-8-2 sample shows an excellent oxygen evolution reaction (OER) activity (134 mV/10 mA cm−2, 40 mV dec−1). The larger double-layer capacitance (Cdl = 17.1 mF cm−2) of the CS4-8-2 sample indicates more electrochemical active sites, compared to the CoS2 and CS4-2 samples. Density functional theory (DFT) calculation proves that due to interface polarization under electric field, the multi-interfaces effectively promote electron transfer and regulate electron structure, thus promoting the adsorption of OH− and dissociation of H2O. Moreover, an innovative norfloxacin (NFX) electrolytic cell (EC) is developed through introducing NFX into the electrolyte, in which efficient NFX degradation and hydrogen production are synergistically achieved. To reach 50 mA cm−2, the required cell voltage of NFX-EC has decreased by 35.2%, compared to conventional KOH-EC. After 2h running at 1 V, 25.5% NFX was degraded in the NFX EC. This innovative NFX-EC is highly energy-efficient, which is promising for the synergistic cleaning and utilization of industry wastewater. The fast electron transfer at Co3S4/Co9S8/CoS2 multi-interfaces promotes water splitting. The efficient hydrogen production and degradation are synergistically achieved in an innovative norfloxacin electrolytic cell (NFX EC). The energy-efficient EC is promising for the cleaning and utilization of industry wastewater. [Display omitted] •Co3S4/Co9S8/CoS2 multi-interfaces effectively improved electron transfer.•Hydrogen production and degradation were synergistically achieved.•After 2h running at 1 V, 25.5% of norfloxacin was degraded at the same time.•35.2% of electricity was economized for norfloxacin-based electrolytic cell.•The energy-efficient system is suitable for cleaning and utilization of wastewater.