Photocatalytic reduction of nitrite (NO₂⁻) to ammonia (NH₃) presents a sustainable path for wastewater remediation and nitrogen resource recovery. However, the sluggish seven-proton/six-electron (7H⁺/6e⁻) transfer kinetics and the formidable energy barrier of hydrogen atom transfer (HAT) limit its practical efficiency. Herein, we report a robust photocatalyst comprising quaternary medium entropy alloy (MEA) nanoparticles (Cu, Co, Ni, Zn) anchored on TiO₂ nanosheets (TNS), featuring a tailor-made crystalline/amorphous heterointerfaces. The unique interfacial architecture synergistically optimizes the bidentate adsorption of nitrite and accelerates water dissociation, thereby lowering the activation energy for active hydrogen (*H) generation. Benefiting from the high-entropy-induced “sluggish diffusion” effect, the amorphous domains exhibit exceptional structure stability against photo-induced recrystallization. Consequently, the HH-CCNZ@TNS catalyst achieves a remarkable NH₃ production efficiency of 99.69% with near 100% selectivity, maintaining superior durability over multiple cycles. This work underscores the potential of entropy engineering in coordinating multi-step proton/electron dynamics for advanced energy and environmental catalysis.