<p>Tandem reactions enable the sequential synthesis of value-added chemicals, as exemplified by the conversion of biomass-derived levulinic acid (LA) to γ-valerolactone (GVL) via hydrogenation and subsequent lactonization, with 4-hydroxyvaleric acid (HVA) as the intermediate. However, achieving such tandem electrocatalysis in a single electrolyzer is challenging because the two steps require distinct pH conditions: the former favors neutral or alkaline media, whereas the latter requires a strongly acidic medium. Here we create a pH gradient at the electrode–electrolyte interface by modifying a Pb electrocatalyst with cetyltrimethylammonium bromide (CTAB). The modified electrocatalyst shows &gt;80% GVL selectivity and &gt;50% Faradaic efficiency (FE) over 50–200 mA cm⁻². Mechanistic studies show that ordered CTAB arrangements on the Pb surface disrupt the interfacial hydrogen-bond network, lowering the local H⁺ concentration near the Pb surface while maintaining higher acidity in the bulk electrolyte, thereby facilitating tandem LA-to-GVL conversion. This study demonstrates distinct microenvironment engineering for tandem electrosynthesis in a single electrolyzer.</p>