Electrode work function and absolute potential scale in solid-state electrochemistry

A two-Kelvin-probe arrangement was used to measure, for the first time in s itu, the work functions, Phi, of the gas-exposed surfaces of porous Pt, Au, and Ag working and reference electrodes exposed to O-2-He, H-2-He and O-2- H-2 mixtures, and deposited on 8% Y2O3-stabilized ZrO2 (YSZ) in a three-ele ctrode solid electrolyte cell. It was found that at temperatures above 600 K the potential difference, U-WR, between the working (W) and reference (R) electrode reflects the difference in the actual, spillover, and adsorption -modified work functions, Phi (W) and Phi (R) of the two electrodes eU(WR) = Phi (W) - Phi (R) [1] This equation, typically valid over 0.8-1 V wide U-WR ranges, was found to hold for any combination of the Pt, Au, and Ag electrodes. It is consistent with the previously reported equation e DeltaU(WR) = Delta Phi (W) [2] which is also confirmed here, and allows for the definition of a natural ab solute electrode potential U-O2 (abs) in solid-state electrochemistry from U-O2(abs) = Phi /e [3] where Phi is the work function of the gas-exposed electrode surface of the metal (any metal) electrode in contact with the YSZ solid electrolyte. It e xpresses the energy of solvation of an electron from vacuum to the Fermi le vel of the solid electrolyte. The value U-O2(0)(abs) = 5.14 +/- 0.05 V was determined as the standard U-O2(abs) value at p(O2) = 1 bar and T = 673 K. (C) 2001 The Electrochemical Society. [DOI: 10.1149/1.1362547] All rights r eserved.