Non-Faradaic Electrochemical Modification of the Catalytic Activity of Pt for H₂Oxidation in Aqueous Alkaline Media

Abstract

The heterogeneous catalytic oxidation of H2 on Pt was investigated on Pt black and Pt−graphite electrodes, also serving as heterogeneous catalysts, in aqueous alkaline solutions as a function of electrode potential and current. Hydrogen−oxygen mixtures were bubbled over the surface of the Pt electrode through a porous Teflon frit, and the rates of H2 and O2 consumption were measured via on-line mass spectrometry and gas chromatography. It was found that positive current application enhances the catalytic rate of H2 oxidation by up to 500% and that the increase in the catalytic rate is up to 100 times larger than the increase I/2F of the electrocatalytic rate corresponding to Faraday's law. The results show that the heterogeneously catalyzed H2 oxidation proceeds in parallel with the electrocatalytic anodic H2 oxidation and that its rate is markedly affected by the catalyst potential and work function. This electrochemically induced and controlled reversible promotion of the catalytic properties of Pt bears many similarities to the effect of electrochemical promotion when using solid electrolytes and can be rationalized by considering the effect of varying potential and work function on the coverages and binding strengths of dissociatively chemisorbed hydrogen and oxygen.

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

“…At higher potentials, where the work function approaches a plateau at 5.75 eV (figure 6), limiting current behaviour is obtained ( figure 7). The observed current-voltage behaviour (figure 7) is practically identical with that obtained during electrochemical promotion studies of H 2 oxidation on Pt|graphite electrodes [32,33]. The absolute potential value of the H + |H 2 electrode, E H þ jH 2 , obtained by extrapolation of the straight line with unity slope in figure 6 for zero NHE potential is 4.46 ± 0.05 V. Careful work is currently underway to obtain a more accurate and precise measurement of the absolute potential of zero NHE potential.…”

“…The situation is similar to that of electrochemical promotion studies of H 2 oxidation by gaseous O 2 on Pt|graphite electrodes [32,33]. Before immersion, the work functions of the Pt working and counter electrode was U O,Pt % 5.03 eV.…”

“…and thus leading to H 2 O formation and to the establishment of a mixed potential, as in the case of electrochemical promotion studies of H 2 oxidation on Pt electrodes [32,33]. The reverse of equation (28) is taking place at the counter electrode.…”

Spillover of primary oxides as a dynamic catalytic effect of interactive hypo-d-oxide supports

“…Nonfaradaic promotion (NEMCA) of hydrogen oxidation on Pt does not impose any facilitating effect in acidic media [61][62][63], but there is no negative anionic influence and the role of hydroxide ions has been inferred to be decisive even in the plentiful of mineral ionic presence. In fact, in alkaline media Eq.…”

Impact of Glass Corrosion on the Electrocatalysis on Pt Electrodes in Alkaline Electrolyte

“…9 However, the consequences of the glass corrosion in alkaline electrolyte on catalytic measurements are generally underestimated. 12,[21][22][23][24][25][26][27] The purpose of the present paper is to show evidence that the impurities due to glass corrosion in alkaline solution cannot be neglected in catalytic measurements. We systematically compare electrocatalytic measurements performed in a homemade electrochemical three-compartment Teflon cell, a material inert in alkaline solution, to measurements performed in the same cell but with the addition of a small piece of Duran glass.…”