Impact of Strain-Induced Changes in Defect Chemistry on Catalytic Activity of Nd₂NiO_4+δ Electrodes

It is well known that defect chemistry plays a vital role in determining the electronic structure, ionic conductivity, and catalytic activity of metal oxides, as demonstrated in perovskite-based oxides to achieve desired functionalities. In this work, we explored the possibility of tuning the defect chemistry and hydrogen oxidation reaction (HOR) activity of Nd₂NiO_4+δ model thin films by controlling the lattice strain. Highly textured Nd₂NiO_4+δ thin films with different strain states were prepared on (110)- and (100)-oriented single-crystal yttrium-stabilized zirconium (YSZ) substrates using pulsed laser deposition. Electrochemical impedance spectroscopy results indicated that the NNO(100) film on the YSZ(110) substrate with larger tensile strain in the a- b plane and compressive strain along the c axis exhibited higher HOR activity than the NNO(110) film on the YSZ(100) substrate at 500-600 °C. The enhancement in HOR activity is attributed to the strain-induced difference in the oxygen defect concentration, as confirmed by high-resolution X-ray diffraction analysis. We believe that the correlation among the strain state, defect chemistry, and catalytic properties is helpful for rational design of more efficient electrode materials.