Absolute potential measurements in solid and aqueous electrochemistry using two Kelvin probes and their implications for the electrochemical promotion of catalysis

摘要

The concept of absolute electrode potential in aqueous and solid electrochemistry is discussed in light of the first experimental investigation utilizing a two Kelvin probe system which allows for direct in situ measurement of the work functions of both the,emersed or spillover modified,working and reference electrodes.In both cases,i.e.emersed electrodes in aqueous electrochemistry and spillover-modified electrodes in solid electrochemistry,it is found that the following two equations relate the working-reference electrode potential difference,U_(WR),and the work functions,PHI_W and PHI_R of the emersed or spillover-modified working and reference electrodes:eU_(WR)= PHI_W-PHI_R(2);e DELTA U_(WR)= DELTA U_W;where U_(WR)is varied either by varying the gaseous composition or via a potentiostat.These equations show that the work function of emersed electrodes in aqueous electrochemistry or of spillover-modified electrodes in solid state electrochemistry is the natural choice of the absolute electrode potential:U_(abs)=PHI_W/e.The value U_(H_2)~0(abs)= 4.46 ± 0.15 V was obtained as the absolute potential value of the H_2/H~+ electrode in aqueous solutions at p_(H_2)=1 bar,pH = 0 and T = 298 K,while the value of U_(O_2)~0(abs)= 5.14 ± 0.05 V was measured as the absolute potential value of the O_2/O~(2-)electrode in YSZ(8 mol% Y2O3-stabilized-ZrO2)at p_(O_2)= 1 bar and T = 673 K.