Three-dimensional Ni3Se4 flowers integrated with ultrathin carbon layer with strong electronic interactions for boosting oxygen reduction/evolution reactions

Transition metal selenides have shown unexpectedly-high activity for oxygen reduction and oxygen evolution reactions (ORR/OER) in alkaline media. However, many fundamental issues regarding the effects of catalyst structure on ORR/OER activities with enhanced stability still remain unknown. Here we prepare three-dimensional (3D) flower-like Ni3Se4 coated by ultrathin carbon-layer (Ni3Se4/UCL) as bifunctional catalyst. Distribution (mapping) of C and N elements confirms the firm combination of Ni3Se4 with UCL to form flower petals with convex-concave surface. Ni3Se4/UCL-3 (mass ratio of NiCl2·6H2O/carbon is 3) exhibits an excellent half-wave potential of 0.82 V (E1/2, ORR) and a promising overpotential of 0.35 V at 10 mA cm−2 (OER). Ni3Se4/UCL-3 has a negative shift of only 12 mV for E1/2 after 5000 cycles (ORR) and a current density decline of only 7.34 % after 20 h test (OER). Density functional theory calculations reveal that interfacial charge redistribution behaviors including charge accumulation and depletion lead to strong electronic interactions between Ni3Se4 (0 0 2) and UCL to obtain efficient charge transfer for ORR/OER. β-NiOOH is mainly responsible for the high OER activity, and in-situ X-ray diffraction tests verify the crystallization of selenite (NiSeO3) during OER. This work provides a promising reference for promoting future development of 3D-structured transition metal selenides-based electrocatalysts.