NiOOH-mediated electron injection into Ti3C2Fx to weaken Ti–H bonds for accelerated photocatalytic hydrogen production

Abstract

Ti₃C₂ MXene (Ti₃C₂T_x), a two-dimensional transition metal carbide, is widely regarded as a highly promising cocatalyst for photocatalytic hydrogen evolution due to its high electrical conductivity and tunable surface terminations. However, the excessively strong Ti–H bond strength in conventional Ti₃C₂ MXene leads to unfavorable hydrogen desorption kinetics, which is further exacerbated due to an overabundance of highly electronegative F-terminations on Ti₃C₂T_x from the F-containing etchant (Ti₃C₂F_x). This study proposes constructing a NiOOH–Ti₃C₂F_x heterojunction to facilitate electron transfer from NiOOH to Ti₃C₂F_x for increasing the Ti 3d antibonding orbital occupancy state. The NiOOH–Ti₃C₂F_x/CdS photocatalysts are prepared through a two-step process, including the initial formation of NiOOH on Ti₃C₂F_x by a precipitation reaction and the subsequent in situ growth of CdS on the NiOOH–Ti₃C₂F_x surface. Photocatalytic hydrogen evolution tests demonstrate that the NiOOH–Ti₃C₂F_x/CdS photocatalyst achieves a significantly enhanced hydrogen production rate of 2.42 mmol h⁻¹ g⁻¹, representing 7.8 times and 4.94 times improvements over pristine CdS and Ti₃C₂F_x/CdS, respectively. DFT calculations and spectroscopic analyses reveal that the electron transfer from NiOOH to Ti₃C₂F_x increases Ti 3d antibonding orbital occupancy, thereby weakening the Ti–H_ads bond. This study provides critical insights into modulating the hydrogen adsorption capacity at Ti sites for efficient solar fuel production.