A comprehensive review on PEM water electrolysis

A comparative investigation was performed to examine the intrinsic catalytic activity and durability of carbon supported Ru, Ir, and Pt nanoparticles and corresponding bulk materials for the electrocatalytic oxygen evolution reaction (OER). The electrochemical surface characteristics of nanoparticles and bulk materials were studied by surface-sensitive cyclic voltammetry. Although basically similar voltammetric features were observed for nanoparticles and bulk materials of each metal, some differences were uncovered highlighting the changes in oxidation chemistry. On the basis of the electrochemical results, we demonstrated that Ru nanoparticles show lower passivation potentials compared to bulk Ru material. Ir nanoparticles completely lost their voltammetric metallic features during the voltage cycling, in contrast to the corresponding bulk material. Finally, Pt nanoparticles show an increased oxophilic nature compared to bulk Pt. With regard to the OER performance, the most pronounced effects of nanosca...

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Electrocatalytic Oxygen Evolution Reaction (OER) on Ru, Ir, and Pt Catalysts: A Comparative Study of Nanoparticles and Bulk Materials

Microkinetic analyses of aqueous electrochemistry involving gaseous H2 or O2, i.e., hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), are revisited. The Tafel slopes used to evaluate the rate determining steps generally assume extreme coverage of the adsorbed species (θ ≈ 0 or ≈1), although, in practice, the slopes are coverage-dependent. We conducted detailed kinetic analyses describing the coverage-dependent Tafel slopes for the aforementioned reactions. Our careful analyses provide a general benchmark for experimentally observed Tafel slopes that can be assigned to specific rate determining steps. The Tafel analysis is a powerful tool for discussing the rate determining steps involved in electrocatalysis, but our study also demonstrated that overly simplified assumptions led to an inaccurate description of the surface electrocatalysis. Additionally, in many studies, Tafel analyses have been performed in conjunction with the Butler-Volmer equation, where its applicability regarding only electron transfer kinetics is often overlooked. Based on the derived kinetic description of the HER/HOR as an example, the limitation of Butler-Volmer expression in electrocatalysis is also discussed in this report.

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Insight on Tafel slopes from a microkinetic analysis of aqueous electrocatalysis for energy conversion.

The mechanism of the oxygen evolution reaction (OER) by catalysts prepared by electrodepositions from Co2+ solutions in phosphate electrolytes (Co-Pi) was studied at neutral pH by electrokinetic and 18O isotope experiments. Low-potential electrodepositions enabled the controlled preparation of ultrathin Co-Pi catalyst films (<100 nm) that could be studied kinetically in the absence of mass transport and charge transport limitations to the OER. The Co-Pi catalysts exhibit a Tafel slope approximately equal to 2.3 × RT/F for the production of oxygen from water in neutral solutions. The electrochemical rate law exhibits an inverse first order dependence on proton activity and a zeroth order dependence on phosphate for [Pi] ≥ 0.03 M. In the absence of phosphate buffer, the Tafel slope is increased ∼3-fold and the overall activity is greatly diminished. Together, these electrokinetic studies suggest a mechanism involving a rapid, one electron, one proton equilibrium between CoIII−OH and CoIV−O in which a phosph...

Mechanistic studies of the oxygen evolution reaction by a cobalt-phosphate catalyst at neutral pH.

https://pubs.rsc.org/en/content/articlepdf/2014/cy/c4cy00669k

Developments and perspectives of oxide-based catalysts for the oxygen evolution reaction

The oxygen evolution reaction on platinum, iridium, ruthenium and their alloys at 80°C in acid solutions

Kinetic parametes were determined for the oxygen evolution reaction on 50–50 atom percent alloys of RuIr, RuPt, and IrPt and compared with results obtained using ruthenium, iridium, platinum, and RuO 2 /TiO 2 electrodes. The potentiostatic studies were made on oxide covered electrodes at 80°C in both 1.0 M H 2 SO 4 and 1.0 M CF 3 SO 3 H. Cyclic voltammetric studies showed that while these noble metals and alloys are about equally effective as electrocatalysts for the hydrogen evolution reaction, striking differences in activity are found for the oxygen evolution reaction. The order of electrocatalytic activity towards oxygen evolution in H 2 SO 4 is Ru > RuIr alloy ∼ RuO 2 /TiO 2 ∼ Ir > IrPt alloy > RuPt alloy > Pt. The type of acid used had very little effect on the kinetic parameters. The lower electrocatalytic activities when platinum is present is probably due to the formation of a platinum oxide film. The dual barrier model is used to interpret the results for the electrodes containing platinum. The best electrocatalysts for oxygen evolution in acid solutions consist of noble metals which form oxide films (RuO 2 , IrO 2 ) possessing metallic characteristics.

E. A. Klaus

Papers

The oxygen evolution reaction on platinum, iridium, ruthenium and their alloys at 80°C in acid solutions

The oxygen evolution reaction on platinum, iridium, ruthenium and their alloys at 80°c in acid solutions