Crystal plane engineering of BiOCl for enhanced chloride-ion storage and saline water deionization performances

Abstract

BiOCl-based materials are promising for chloride-ion storage and saline water deionization; however, their limited intercalation contributions and slow reaction kinetics hinder cyclability and chloride-ion storage capacities. In this work, crystal plane engineering using a simple pH adjustment method optimizes the crystallographic orientation and grain sizes of BiOCl, resulting in improved chloride-ion storage performances in aqueous-based electrochemical systems. When paired with an Ag electrode, samples demonstrate an exceptional chloride-ion storage capacity of 122.61 mAh g⁻¹ at 0.3 A g⁻¹ with excellent capacity retention of 90.1 % after 120 cycles and exhibit a rate capacity of 85.12 mAh g⁻¹ at 2 A g⁻¹. In desalination systems (paired with a Prussian blue electrode), they achieve a desalination capacity of 74.75 mg g⁻¹ at 1.2 V and maintain a capacity of 58.47 mg g⁻¹ after 30 cycles. DFT calculations and experiments reveal that increased exposure of the (110) crystal plane could slightly reduce chloride ion diffusion coefficients and hinder charge transfer while enhancing pseudocapacitive contributions. In-situ XRD results further confirm that crystallographic orientation promotes a higher proportion of intercalation reactions, improving electrode utilization and reversibility. This trade-off between ion diffusion, pseudocapacity, and reaction reversibility leads to superior electrochemical performances, providing insights for optimizing BiOCl-based anodes for long-term stability and multifunctional applications in chloride-ion storage and saline water deionization.