Rethinking electrolyzer design for optimal waste-heat utilization

Green hydrogen and electric heating have received attention as separate solutions to make more sustainable material and energy supply networks. Waste-heat utilization from electrolysis has been shown to improve the performance of the process. However, this aspect is usually added a posteriori to an electrolyzer optimized for hydrogen production only, thus limiting the potential benefits of waste-heat utilization. In contrast, the explicit design of electrolyzers with waste-heat upgrading using heat pumps has not been sufficiently explored. This work analyzes the benefits of designing electrolyzers with waste-heat utilization in mind under different operating conditions to supply heat at different temperature levels, and compares their performance with other electric heating options. Designing for waste-heat utilization leads to more compact electrolyzers with higher current densities, improving the energetic, exergetic, economic and environmental performance of water electrolysis. Such an alternative design can reduce costs by up to 30 % and reduce net emissions by a factor of four compared to using the waste heat a posteriori. When optimizing supply networks to provide both hydrogen and heat, waste-heat utilization from electrolyzers is preferred over air-source heat pumps and direct electric heaters. Furthermore, waste-heat upgrading via heat pumps to higher temperatures is preferable to direct use at lower temperatures if medium-temperature heat is sufficiently more valuable than low-temperature heat. These findings suggest that incorporating waste-heat utilization into the electrolyzer design could create synergies, making it a promising solution to be further explored.