Evaluating Overpotentials in GDC Electrodes for H_2/H_2O Reactions in Solid Oxide Electrochemical Cells

摘要

Thin-film GDC (Ce_(0.8)Gd_(0.2)O_(2-x) 300 nm thick) electrodes with porous Ni or Au metal overlayers (300 nm thick) were sputter-deposited on polycrystalline YSZ substrates and tested in single-chamber cells. With a back-side Pt-counter electrode, the electrochemical cells were characterized by linear-sweep voltammetry and impedance spectroscopy between 650 to 750°C in mixtures of H_2/H_2O/Ar diluent. To complement the electrochemical tests, ambient-pressure XPS at the Advanced Light Source was performed on active cells in H_2/H_2O mixtures to measure surface potential and oxidation states. The GDC electrodes showed lower resistance to H_2O electrolysis than H_2 oxidation with Ni and Au overlayers. XPS measurements indicated large overpotentials across the YSZ/GDC interface particularly for H_2 oxidation on the GDC electrode. Increasing P_(H2)/P_(H2O) (up to 10) resulted in higher rates for not only H_2 oxidation, but also H_2O electrolysis, suggesting that H_2O electrolysis activity is enhanced by increased reduction of the GDC surface.