Hydrogen is an environmentally friendly alternative to conventional fossil fuels and is considered as a renewable energy carrier for meeting the ever-increasing energy demand. Although hydrogen is abundant on earth in the form of compounds such as water, producing molecular hydrogen demands a large amount of energy. A solid oxide electrolysis cell (SOEC) is an electrochemical device which generates hydrogen from various sources. An SOEC uses high temperature (>800°C) to electrolyse water with high efficiency assisted by thermodynamically favoured water splitting that enables large-scale hydrogen production. This review provides a comprehensive overview of the current status in the developments of high-temperature steam electrolysis using a proton- and oxygen-ion-conducting SOEC system for hydrogen production. The present review summarises the detailed approaches for hydrogen production using SOECs, basic principles, challenges in designing hydrogen and oxygen electrodes and electrolytes, and potential solutions to durability issues.

With increasing global interest in renewable energy technology in the backdrop of climate change, storage of electrical energy has become particularly relevant. Most sustainable technologies (e.g. wind, solar) produce electricity intermittently. Thus, converting electrical energy and base molecules (i.e. H2O, N2) into energy rich ones (e.g. H2, NH3) or chemical feedstock (e.g. NO) is of paramount importance. While H2O splitting is compatible with renewable electricity, N2 fixation is currently dominated by thermally activated processes. In this work, we demonstrate an all-electric route for simultaneous NO and H2 production. In our approach, H2O is reduced to H2 in the cathode of a solid oxide electrolyser while NO is produced in the anode by the reaction of O 2species (transported via the electrolyte) and plasma activated N2 species. High faradaic

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smtd.202100868.

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