Unveiling the Transformative Potential of SWCNT/In₂O₃ Heterostructures as High-Performance Catalysts for Overall Water Splitting

In this paper, we studied the synthesis of In₂O₃/SWCNT heterostructure catalysts by blending single-walled carbon nanotubes (SWCNTs) in In₂O₃ nanomaterial during an in situ and facile one-step hydrothermal method for the application of electrocatalytic overall water splitting (OWS). Interestingly, it is predictable that the SWCNTs and In₂O₃ have different vacuum levels, which could play a crucial role in charge transfer by band engineering when both are brought into direct contact (surface or interface or both) to form the In₂O₃/SWCNT heterostructure. Remarkably, we discussed the possibilities of surface and interface engineering during In₂O₃/SWCNT heterostructure formation, which regulates and enhances the hydrogen and oxygen reaction kinetics. Consequently, the In₂O₃/SWCNT-4 catalyst illustrates the lowest overpotential values of 337 and 141 mV during the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, compared with other catalysts in an alkaline medium. It may be because adding SWCNTs accelerates the mass transport and segregation of water molecules and enriches the adsorption and desorption free energy of hydrogen intermediates, providing more active sites and improving intrinsic catalytic activities. The Tafel slope values of the OER are 175.1 and 116.1 mV dec^-1 for the pure In₂O₃ catalyst and In₂O₃/SWCNT-4 (5.0 mL of SWCNTs) heterostructure catalyst, suggesting that the SWCNTs can regulate the charge-transfer rate, which can play a crucial role in determining the rate-controlling steps of oxygen and hydrogen evolution reactions. The In₂O₃/SWCNT-4 catalyst shows excellent stability over 24 h of the HER (at −10 mA cm^-2) and 24 h of the OER (at 10 mA cm^-2) using chronopotentiometry (CP). Further, the overall water splitting of the In₂O₃/SWCNT-4 || In₂O₃/SWCNT-4 cell shows excellent OWS activities with the lowest cell potential of 1.58 V and excellent stability over 25 h at 10 mA cm^-2. In addition, water splitting mechanisms are discussed schematically to visualize the insights into the Schottky barrier formation by surface and interface engineering in the In₂O₃/SWCNT heterostructure.