Efficient evolution of hydrogen and oxygen simultaneously with earth-abundant, highly active, and robust bifunctional electrocatalysts has been a significant concern for water splitting. Herein, non-noble metal based Ni-Co-S bifunctional catalysts with tunable stoichiometry and morphology were realized. The electronic structure engineering and subsequent morphological design synergistically contributed to significantly elevated electrocatalytical performance. Overpotentials η10 of 243 mV (vs.RHE) for OER and 80 mV for HER in 1M KOH solution, as well as Tafel slopes of 54.9 mV/dec for OER and 58.5mV/dec for HER were demonstrated together with prominent stability. In addition, DFT calculation was conducted to indicate the optimal electronic structure via visually mapped electron density difference of catalysts, and representatively verify that the enhanced OER activity of NiCo2S4 nanosheets is concerned with the Co top site on (110) surface. Moreover, the tandem bifunctional NiCo2S4 anode and cathode exhibited a required voltage down to 1.58V (J=10 mA/cm2) for simultaneous OER and HER, and no obvious performance decayed after 72 h. When integrated with a GaAs solar cell, such photo-assisted water splitting electrolyzer acquired a certificated solar-to-hydrogen efficiency up to 18.01%, further demonstrating the feasible engineering protocols as well as the promising potential of bifunctional NiCo2S4 for large-scale overall water splitting.^{[1, 2]}

References

[1] H. Kim, K. Kang, et.al., Nat. Commun. 2015, 6, 8253.

[2] H. Wang, Y. Cui, et.al., Nat. Commun. 2015, 6, 7261.