Mesoporous reduced graphene oxide/WSe ₂ composite particles for efficient sodium-ion batteries and hydrogen evolution reactions

Mesoporous WSe ₂ -reduced graphene oxide (WSe ₂ -rGO) composite particles were prepared by spray pyrolysis and subsequent selenization. The WSe ₂ -rGO composite particles had both well-dispersed rGO nanosheets and well-faceted WSe ₂ nanocrystals with plenty of folded edges. As a comparison sample, hierarchical structured WSe ₂ particles were produced by selenization of the bare WO ₃ particles obtained by spray pyrolysis. The WSe ₂ -rGO composite particles showed superior electrochemical properties for sodium-ion batteries (SIBs) and electrocatalytic efficiencies for hydrogen evolution reactions (HERs) compared to those of the bare WSe ₂ particles. The discharge capacities of the WSe ₂ -rGO composite particles and bare WSe ₂ particles for the 100th cycle at a current density of 0.5 A g ⁻¹ for sodium-ion storage were 238 and 36 mA h g ⁻¹ , respectively; their corresponding capacity retentions measured from the third cycle were 80% and 13%. The WSe ₂ –rGO composite particles showed much lower onset potential and larger current density (36.5 mA cm ⁻² at η = 300 mV) than those of the bare WSe ₂ particles (0.61 mA cm ⁻² at η = 300 mV). The Tafel slopes for the WSe ₂ –rGO composite and bare WSe ₂ particles were approximately 60 and 115 mV dec ⁻¹ , respectively.