[Objective] To overcome the carbon penalty of limestone‑gypsum desulfurization in coal‑fired power plants and the poor utilization of dilute SO2, this study proposes an integrated technology combining ammonia‑based absorption with SO 2‑depolarized electrolysis (SDE) for simultaneous flue gas desulfurization and hydrogen production. The goal is to achieve zero‑carbon‑increase desulfurization, low‑energy hydrogen generation, high‑value by‑product recovery, and flexibl e load regulation to support next‑generation coal power upgrading. 

[Methods] A laboratory‑scale coupled system consisting of an ammonia absorption tower and a membrane electrolyzer was constructed. The anodic performance of an acidic sulfate system (0.5 mol/L H 2SO4) and an ammoniacal system (1% ammonia water) was compared under constant‑voltage electrolysis at 1.2 V and 1.4 V 2 using real flue gas ( 2 290~11 400 mg/m3 SO2). Current efficiency and hydrogen production energy consumption were calculated via F araday’s law. Density functional theory (DFT) calculations were performed to reveal the reaction mechanism, and a techno‑economic assessment was carried out for a 400 000 m3/h flue gas treatment scale. 

[Results] In the acidic sulfate system, physical dissolution of SO2 is severely limited by Henry’s law; at 1.2 V the current density was only 0.4 mA/cm2, and voltage surged rapidly due to reactant depletion, indicating an insurmountable mass‑transfer bottleneck. In contrast, the ammoniacal system chemicall y absorbs SO 2 to form ammonium sulfite, greatly increasing the concentration of electroactive species. Constant‑voltage electrolysis in the ammoniacal system at 1.2 V gave an average current of 0.298 A, a current efficiency of 76.9%, and a hydrogen energy consumption of 3.45 kW·h/m3; at 1.4 V , the average current increased to 0.768 A, the current efficiency rose to 87.5%, and the energy consumption was 3.83 kW·h/m3. The higher current efficiency at 1.4 V , despite being above the theoretical water‑spl itting voltage, indicates that the increased overpotential accelerates kinetics and enhances bubble‑induced convective mass transfer, compensating for minor oxygen evolution. DFT calculations show that the activation energy for sulfite oxidation in the ammoniacal system is 0.62 eV , which is 32% lower than that in the acidic system (0.91 eV), owing to stronger chemisorption of sulfite on graphite. For the 400 000 m3/h scale, the system achieves a desulfurization efficiency ≥98.5%, producing 7.2 million m3 of hydrogen and 22 000 t of ammonium sulfate annually. The annual net profit is estimated at 20.6~31.5 million yuan with a payback period of 3~4 years, based on current market prices. Sensitivity analysis shows that hydrogen and ammonium sulfate prices are the most influential factors, while the electrolyzer’s fast load response (0~100% within 5 s) can participate in grid peak‑shaving, yielding additional revenue. 

[Conclusion] The ammonia‑absorption‑ coupled SDE technology overcomes the mass‑transfer and kinetic limitations of dilute SO 2 electrolysis by combining chemical absorption with a low‑activation‑energy anodic reaction. It enables zero‑carbon‑increase desulfurization, low‑energy hydrogen production (about 20% lower than conventional water electrolysis), and high‑value fertilizer co‑production, while the flexible electrolysis load supports deep peak shaving and low‑load combustion stability via hydrogen co‑firing. This integrated approach offers a technically viable and economically attractive pathway for the clean and flexible transformation of coal‑fired power generation under China’s carbon‑neutral strategy.