<p>Hydrogen evolution coupled with selective oxidation of organic molecules (such as methanol) via electrocatalytic or (photo)electrochemical route, offers an energy-efficient strategy for producing clean energy and value-added chemicals, yet remains hindered by sluggish interfacial charge-transfer kinetics and poor product selectivity. To unravel these interfacial processes, photocatalytic systems, wherein photogenerated charges drive redox half-reactions, not only mirror the essential charge-transfer steps in (photo)electrocatalysis, but also provide a self-contained micro-reaction environment, enabling direct probing of the intrinsic “catalyst/reactant/solvent” interface through in-situ and time-resolved spectroscopies to capture charge-transfer dynamics and key reaction intermediates. Herein, metal-anchored TiO₂ serves as a model catalyst and hydrogen evolution coupled with methanol oxidation is chosen as a probe reaction to elucidate the intrinsic link between interfacial charge transfer and catalytic performance. An apparent quantum yield of 94% and activity of 53.7 mmol g^-1 h^-1 for H₂ production are both achieved via Pt/TiO₂, with a near-unity selectivity (~ 99%) for both H₂ and formaldehyde. A series of transition metal cocatalysts (Pd, Rh, Ru, Ni, Co, Au, Ag) demonstrate similar enhancement, showing a broad applicability of this interface-engineering approach. Comprehensive photoelectrochemical and photophysical characterizations reveal that anchored metals, acting as effective interfacial-charge regulators, significantly enhance charge separation, prolonging carrier lifetimes and lowering charge-transfer resistance. Mechanistic studies identify the ∙CH₂OH radical as a key intermediate, steering the reaction toward selective oxidation of methanol. This study provides fundamental insights into interfacial charge-transfer kinetics and establishes a universal design principle for high-performance (photo)electrocatalytic interfaces for hydrogen production.</p> Graphical abstract <p></p>