Millimeter tubular solid oxide electrolysis cells with modified asymmetric hydrogen electrode

•Hydrogen electrode with pore gradient is fabricated for SOEC.•An additional graphite layer is employed to remove the relative dense skin layer.•The asymmetric structure can eliminate the steam starvation.

Asymmetric structure with pore gradient is fabricated as the hydrogen electrode for millimeter tubular solid oxide electrolysis cells (SOECs). The gradient electrode is achieved with a graphite-assistant phase inversion process using an additional graphite layer to remove the relative dense skin layer. The electrode has demonstrated higher gas permeability than that with normal composite structure. Consequently, the steam starvation (concentration polarization) is successfully eliminated when SOEC is operated at relatively high voltage and low steam concentration. In addition, reduced interfacial polarization resistance and elevated current density are achieved for the tubular SOEC with the unique electrode.