Within the framework of developing reversible solid oxide fuel cells/solid oxide electrolysis cells (SOFCs/SOECs), we have engaged in the design of high-performance electrodes. Facile production of hollow spherical particles of samaria-doped ceria (SDC) decorated with Ni–Co alloy catalysts (Ni_100−XCo_X/SDC, X = 0–50 atom%), nanometers in size, was adopted. A distinctive microstructure was observed in the hydrogen electrode fabricated with this composite powder. The cobalt addition played a significant role in evolution of the microstructure and effectively enlarged the electrochemical reaction zone. Under SOFC/SOEC reversible operation, the optimal performance characterized by a comparatively low ohmic resistance and high electrocatalytic activity was achieved with the Ni₈₀Co₂₀/SDC composition. At 900 °C and an overpotential of 0.1 V, the current density reached remarkably high values of 0.18 and 0.37 A cm⁻² in SOFC and SOEC operation, respectively.