The nickel(Ni)-patterned electrode enables researchers to quantify the triple-phase boundary (TPB) length and Ni surface area, exclude the influence of bulk gas diffusion and clearly separate the active regions of the chemical/electrochemical reactions. This tool has been studied for identifying the reaction mechanism in SOFC but rarely in SOEC. In this study, the Ni-patterned electrodes with the stripe width of 100 μm were tested in both the solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes at the atmosphere of H₂O/H₂ and further H₂O/CO₂/H₂/CO. The experimental test shows the stability of the Ni-patterned electrode in the H₂O/H₂ atmosphere was much poorer than that in the CO/CO₂ atmosphere due to the nickel reacting with steam. Thus, the Ni-patterned electrode needed to operate at a temperature of ≤700^oC with the inlet H₂/H₂O molar ratio of >7 and the current-applied time shouldn’t be over 5 h to keep the accuracy of the TPB length and Ni surface area. The effects of the temperature, partial pressure of H₂O and H₂ are investigated. The activation energy of the Ni-patterned electrodes was 0.386 eV. The electrochemical performance had a positive correlation with both the partial pressure of H₂ and H₂O, especially showed higher sensitivity to the partial pressure of H₂O. Further, a possible mechanism of the H₂O/H₂ electrochemical conversion was proposed according to the experimental data and existing literature, which contains two-step charge-transfer reaction: H(Ni)+O^2-(YSZ)OH^-(YSZ)+(Ni)+e^- and H(Ni)+OH^-(YSZ)H₂O(YSZ)+(Ni)+e^-. Based on the experiments, an analytical calculation was performed to investigate the rate-determining steps in the Ni-patterned electrodes by bridging the connection between the kinetic parameters and operating conditions. The results indicate the rate-limiting steps may be different for the SOFC and SOEC modes. In SOFC mode, the H₂ electrochemical oxidation could depend more on the charge-transfer reaction H(Ni)+O^2-(YSZ)→OH^-(YSZ)+(Ni)+e^-, however in SOEC mode, the rate-determining step of the H₂O electrochemical reduction should be H₂O(YSZ)+(Ni)+e^-→OH^-(YSZ)+H(Ni). In this way, a reversible mechanism could be applied for reversible SOFC (RSOFC) to describe the conversion between hydrogen and steam by different charge-transfer-reaction domination in the SOFC and SOEC mode.