Review—Challenges and Opportunities for Increased Current Density in Alkaline Electrolysis by Increasing the Operating Temperature

The highly-efficient, low-cost, large-scale production of green hydrogen by means of electrolysis is urgently needed for achieving a decarbonized energy supply. Alkaline water electrolysis is a wellestablished technology with relatively low costs which does not require scarce noble metal catalysts, but it suffers from low current densities. Increasing the operating temperature can allow this limitation to be overcome. This article summarizes both long-standing and recent developments in alkaline water electrolysis at increased temperature and sheds light on the challenges and unique opportunities of this approach. It is found that electrochemical improvements induced by higher temperature enable competitive current densities and offer unique possibilities for thermal management. The selection and development of stable materials, catalysts, and diaphragms is challenging, but some have proven long-term stability up to at least 150 °C and promising candidates are available at up to 200 °C. Further research will allow the present challenges to be overcome by understanding and improving the basic processes and components for alkaline electrolysis at increased temperature and capitalizing on its unique advantages.