<p>The development of low platinum-loading catalysts for the economically viable hydrogen evolution reaction (HER) remains challenging. Herein, a precursor dilution strategy is used to fabricate Pt nanoclusters anchored on Ni-embedded porous carbon microspheres. The approach begins with the facile synthesis of Zn/Ni-based coordination polymers (Ni-BTC-Zn) due to the isomorphic substitution of Zn²⁺ and Ni²⁺. During pyrolysis, the evaporation of zinc species results in a highly porous carbon structure with well-dispersed nickel nanoparticles. Subsequent solvothermal treatment allows for the uniform deposition of Pt nanoclusters to form the final bimetallic PtNi catalysts (PtNi-BTC-C). Among them, the optimized PtNi-BTC-C10 exhibits exceptional alkaline HER performance, requiring an overpotential of only 41 mV to achieve 10 mA cm⁻² and a low Tafel slope of 31.1 mV dec⁻¹. It also demonstrates outstanding durability with a current retention of 90.7% after 70 h, far exceeding Pt/C. Extensive characterization confirms that moderate Zn dilution optimally modulates the Ni particle size and dispersion, leading to maximized active sites and enhanced charge transfer. Combined with DFT calculations, the Pt-Ni-cluster model for PtNi-BTC-C10 possesses an optimized electronic structure with a shifted d-band center, which facilitates water dissociation and optimizes H* desorption with the most favorable energetics (0.262 eV). This work provides a fundamental understanding of precursor dilution engineering and offers a versatile pathway for designing advanced noble-metal-based bimetallic electrocatalysts.</p>