Solar energy conversion has been studied extensively to combat the energy-crisis and improve upon the generation of renewable energy. Among these, solar driven photocatalytic water splitting offers immense benefits for clean and sustainable hydrogen generation. Semiconductor nanoparticles are commonly used for water splitting due to their controllable band gaps and surface structures. Among the numerous geometrically shaped nanoparticles, one-dimensional (1D) core/shell seeded nanorods have shown great promise due to their ability to quantum confine holes in the radial direction while maintaining charge separation along the axial direction. The key bottleneck for efficient hydrogen evolution from these semiconductor nanorods, and their long-term stability, was proven to be the rate at which photoexcited holes are extracted. Several works have been conducted to increase the efficiency of hole extraction through use of different hole scavengers, ligands, and redox shuttles. However, little work has been conducted to tune the width, one of the most important parameters that directly controls the availability of the holes on the nanorods’ surface. Here, I will present the means by which we successfully attained well-defined control over the nanorods’ width, with a single monolayer precision. This level of width control has allowed us to greatly improve the rate at which holes are extracted, leading to unity photocatalytic hydrogen evolution efficiency at demanding redox potential conditions.