Self-Assembled NbOPO4 Nanosheet/Reduced Graphene Oxide Heterostructure for Capacitive Desalination

Capacitive deionization (CDI) is a promising and energy-efficient technology for desalination. The development of high-performance capacitive electrodes is essential for enhancing the CDI properties for practical applications. Here, a 2D heterostructure was rationally designed and synthesized by face-to-face restacking of NbOPO4 nanosheets and reduced graphene oxide (rGO) via an electrostatic self-assembly process. The as-prepared 2D NbOPO4/rGO heterostructure achieved an excellent ion storage capacity, electronic conductivity, and unimpeded ion kinetics. When applied as electrodes for CDI, the 2D NbOPO4/rGO heterostructure delivered a high specific capacitance of 258.3 F g–1 and an electrosorption capacity of 73 mg g–1 for NaCl solution of 10 000 mg L–1 at an applied voltage of 1.2 V, which is more than five times larger than that of activated carbon. The heterostructure electrode also showed high desalination stability for up to 50 adsorption/desorption cycles. The high CDI performance is attributed to the strong 2D/2D coupling between NbOPO4 nanosheets and rGO. The strong 2D/2D coupling reduced the charge transfer resistance, affirmed via the electrochemical impedance spectroscopy technique, attesting to the enhanced charge transportation across the heterointerface. The robust 2D/2D coupling was affirmed via the uniform and identical Raman shifts at various random regions, and larger XPS binding energy shifts for the self-assembled NbOPO4/rGO heterostructure. This work demonstrated the potential of self-assembled nanoheterostructures for water desalination via capacitive deionization.