Some water electrolysers like alkaline electrolyser cells (AEC) and polymer electrolyte membrane electrolyser cell (PEMEC) have been commercially available for many decades, but for production of hydrogen for fuel using renewable electricity they are not yet affordable because of a too low ratio of production rate/cost. Production rate is determined mainly by electrode kinetics. Therefore, parallel to improving the electrodes of these electrolyser cells, other cell types, which have faster electrode kinetics, can electrolyse CO2 and have potential lower investment costs, are being researched and developed. Solid oxide electrolyser cell (SOEC) has a solid oxide ion conductor as electrolyte, often yttria stabilised zirconia (YSZ). The cathode (CO evolution, negative) is often a Ni-YSZ composite. The anode (O2 evolution, positive) most often consists of a composite of YSZ electrolyte and an electron conducting perovskite structured oxide, e.g. (La0.75Sr0.25)0.95MnO3. A cell consisting of these materials can operate in the range of 650 � 950 �C. Solid proton conducting electrolyzer cell (SPCEC) has a proton conducting solid oxide electrolyte, e.g. yttria doped barium zirconate, BaZr0.85Y0.15H0.15O3, i.e. ceramics that can take up H2O and become proton conducting. Electrodes may be similar to those used for SOEC. It may be operated between 500 � 700 �C. Molten carbonate electrolyser cell (MCEC) has molten Li2CO3 electrolyte, Ti-Al-metal alloy as cathode (CO evolution) and graphite as anode (O2 evolution), and may be operated above 800 �C.A short review of the various types is presented, and the limitations of the kinetics are described. The pros and cons of high temperature and pressure as measures to increase the electrode kinetics are discussed. Naturally, the reaction rates increase with temperature and in most cases also with pressure, but high temperature and pressure put high demands to cell, stack and system materials even though the electrocatalysts in general are much cheaper.

Electrochemical reduction of CO<sub>2</sub> and H<sub>2</sub>O into fuels: Cell types and kinetic barriers

246th National Meeting (2013)

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Electrochemical reduction of CO2 and H2O into fuels: Cell types and kinetic barriers

Electrochemical reduction of CO₂ and H₂O into fuels: Cell types and kinetic barriers