Integrating Ru nanoparticles and single-atom sites in Ni-YSZ fuel electrodes for enhanced steam electrolysis in solid oxide electrolysis cells

Solid oxide electrolysis cells (SOECs) can convert renewable electricity into hydrogen through steam electrolysis, supporting sustainable energy storage. Conventional Ni-yttria-stabilized zirconia (Ni-YSZ) fuel electrode is widely used in SOECs, yet it suffers from limited active sites and sluggish intrinsic activity for steam electrolysis. Here, we address these limitations through partial Ru exsolution, generating Ru nanoparticles alongside retained single-atom Ru sites to expand catalytic interfaces and enhance intrinsic kinetics. Specifically, Ru is doped into YSZ, yielding (Y0.148Zr0.852)0.97Ru0.03O2-δ (YSZRu). During high-temperature reduction, partial Ru exsolves onto the oxide surface, accompanied by oxygen vacancy formation, while residual Ru remains atomically dispersed within the oxide lattice. Ru modification introduces additional sites for H2O conversion beyond the existing Ni-oxide-gas triple-phase boundaries, including nanoscale Ru-oxide-gas interfaces and surface-accessible lattice Ru sites that cooperate with oxygen vacancies, thereby enhancing steam electrolysis activity. Consequently, the SOEC incorporating the Ni-YSZRu electrode achieves an electrolysis current density of 0.58 A cm−2 at 750°C and 1.3 V, more than twice that of its Ni-YSZ counterpart, and maintains stable electrolysis operation for 100 h at 700°C.