Unveiling general rules governing the dimensional evolution of branched TiO2 and impacts on photoelectrochemical behaviors

Abstract

Branched nanostructures represent a unique group of nanoarchitectures exhibiting an advantageous high surface area and excellent charge transport for energy conversion applications compared to their bulk counterparts. Especially, branched titanium dioxide (TiO₂) has been reported as a promising photocatalyst in several applications. However, precise control of its nanostructures and crystal phases remains challenging. Normally, branched TiO₂ nanostructures (BTNs) have been fabricated by a multi-step synthesis, and only a particular dimension is achieved. Herein, we present generic rules governing the structural evolution of BTNs from zero-dimensional (0D) to one-dimensional (1D) and two-dimensional (2D) structures by a facile one-pot hydrothermal synthesis with controlled isotropic and anisotropic crystal growth and symmetry breaking. Various dimensional BTNs with a controllable number of branches and crystal phases are obtained. In addition, these nanoarchitectures are directly grown on a conductive substrate and could be readily used as a photoelectrode. The dimension-dependent photocatalytic behaviors are carefully investigated in photoelectrochemical (PEC) water splitting. An optimized 1D nanostructure produces a photocurrent density of up to 0.87 mA cm⁻² at 1.23 V vs. RHE. The excellent PEC performance could be attributed to the appropriate band alignment and the unique structure that is beneficial for charge transport and separation.