Investigation on surface metal vacancy electrochemistry

Surface bismuth vacancies favor for the adsorption and accumulation of Na(I) ions on electrode surface, but refrains the desorption of Na(I) ion from surface. [Display omitted] •Surface bismuth vacancy favors for adsorption and accumulation of ions on electrode surface.•Surface bismuth vacancy can refrains the desorption of ions from electrode surface.•BiOCl with surface bismuth vacancy has a capacitance 3.4 times higher than that without.•This study provides a new strategy to develop an excellent electrode material. In this work, BiOCl nanosheets with and without surface bismuth vacancy (VBi-BiOCl and BiOCl) are prepared by a simple hydrothermal method. The formation of surface bismuth vacancy is confirmed mainly by XPS, EPR, PL, and UV-DRS. It is found that although BiOCl has a higher BET area (16m2g−1) and a lower electrical resistance (2.62Ω) than VBi-BiOCl (4m2g−1, 6.33Ω), the specific capacitance (23.6 mF cm−2) of VBi-BiOCl is 3.4 times higher than that (6.9 mF cm−2) of BiOCl at 0.5mAcm−2. However, the improved capacitance has been mainly attributed to the formation of surface bismuth vacancies, which could provide excess electrochemically adsorption sites for Na (I) ions. This finding is obviously different from conventional viewpoint that the available electrochemically active surface and electrical conductance are usually regarded as the crucial factors for the electrochemical performance. Hence, this work provides a new idea to develop excellent electrode materials.