An energy storage system includes: a combustion turbine configured to output heated sweep gas; a reformer configured to receive natural gas and steam and to output reformed natural gas; a molten carbonate electrolyzer cell (“MCEC”) comprising an MCEC anode and an MCEC cathode, wherein the MCEC is configured to operate in a hydrogen-generation mode in which: the MCEC anode receives the reformed natural gas from the reformer, and outputs MCEC anode exhaust that contains hydrogen, and the MCEC cathode is configured to receive heated sweep gas from the combustion turbine, and to output MCEC cathode exhaust; and a storage tank configured to receive the MCEC anode exhaust that contains hydrogen.