Understanding the electrocatalytic activity of transition metal nanoparticles for solid oxide cell fuel electrodes

In this work, we utilized the concept of decoupling the electrocatalytic activity from the current conducting phase of solid oxide cell fuel electrodes to investigate the electrochemical performance of three different transition metals, namely Ni, Co, and Fe. It was found that the nickel and cobalt infiltrated cells had comparable performances in both 4% H₂O/H₂ and 50% H₂O/H₂. Furthermore, iron nanoparticles were found to be the better electrocatalyst at low pO₂ values, however at higher pO₂ values the iron infiltration became the inferior catalyst. Investigating the temperature dependence of the polarization resistance in terms of activation energy and pre-exponential factor showed interesting differences between the metal catalysts and a dependence on the gas atmosphere. The results were analyzed by developing a model based on the harmonic oscillator, the model allows for correlating changes in activation energy and pre-exponential factor with kinetic parameters of the electrode reaction. The model indicates that at higher pO₂ values, iron nanoparticles experience a surface blockade, i.e. strong bonding of the reactants to the catalytic sites. For the nickel electrocatalyst, an increase in steam content according to the model leads to an increase in the turnover frequency, which is in good agreement with earlier reports in literature.