Waste-heat upgrading from alkaline and PEM electrolyzers using heat pumps

The use of waste heat from electrolysis can significantly increase process efficiency. Alkaline and PEM electrolyzers, the most mature technologies, produce low-temperature waste heat. Most studies focus on using this waste heat for low-temperature applications like district heating. Alternatively, this waste heat can be upgraded to a temperature that can be usable in the chemical industry, e.g., for steam generation. The combination of an alkaline electrolyzer with a heat pump has been recently investigated to supply both hydrogen and medium-temperature heat. Optimizing electrolyzers for both hydrogen and heat production (combined design) has been shown to have advantages over optimizing for hydrogen only and upgrading the waste heat a posteriori (separate design). However, the effects of electrolyzer pressure and hydrogen compression were not considered, and it remains unclear if similar benefits apply to PEM electrolyzers. This work further analyzes the combined system (i.e., electrolyzer with a heat pump) by including hydrogen compression and comparing alkaline and PEM electrolyzers. The results show that designing with waste-heat utilization in mind benefits both alkaline and PEM at low and high pressures. The combined design allows up to 10% cost reduction and up to fourfold reduction in CO2 emissions compared to the separate design. However, this benefit is constrained by the maximum achievable current density, particularly for PEM. Despite this limitation, the combined system can effectively supply hydrogen and heat across various energy price scenarios, making it a promising solution for hydrogen supply and industrial electric heating.