Delivering the Full Potential of Oxygen Evolving Electrocatalyst by Conditioning Electrolytes at Near‐Neutral pH

Abstract

This study reports on the impact of identity and compositions of buffer ions on oxygen evolution reaction (OER) performance at a wide range of pH levels using a model IrOx electrocatalyst. Rigorous microkinetic analysis employing kinetic isotope effects, Tafel analysis, and temperature dependence measurement was conducted to establish rate expression isolated from the diffusion contribution of buffer ions and solution resistance. It was found that the OER kinetics was facile with OH− oxidation compared to H2O, the results of which were highlighted by mitigating over 200 mV overpotential in the presence of buffer to reach 10 mA cm−2. This improvement was ascribed to the involvement of the kinetics of the local OH− supply by the buffering action. Further digesting the kinetic data at various buffer pKa and the solution bulk pH disclosed a trade‐off between the exchange current density and the Tafel slope, indicating that the optimal electrolyte condition can be chosen at a different range of current density. This study provides a quantitative guideline for electrolyte engineering to maximize the intrinsic OER performance that electrocatalyst possesses especially at near‐neutral pH.

Selective Electrooxidation of Biomass‐Derived Alcohols to Aldehydes in a Neutral Medium: Promoted Water Dissociation over a Nickel‐Oxide‐Supported Ruthenium Single‐Atom Catalyst

“…[39,40] In order to reveal the role of water dissociation during HMFOR over Ru 1 -NiO at neutral pH, we carried out in situ electrochemical Raman spectroscopy measurements to study the water dissociation behavior by monitoring the pH value at electrode surface (Figure S24). [45,46] Figure 4d shows the calculated pH values.…”

“…It is believed that, for electrooxidation in the neutral medium, OH* would be largely provided by the water dissociation with proton and electron transfer (H 2 O→OH*+H + +e − ) [39, 40] . In order to reveal the role of water dissociation during HMFOR over Ru 1 ‐NiO at neutral pH, we carried out in situ electrochemical Raman spectroscopy measurements to study the water dissociation behavior by monitoring the pH value at electrode surface (Figure S24) [45, 46] . Figure 4d shows the calculated pH values.…”

Oxygen Evolution Activity of Amorphous Cobalt Oxyhydroxides: Interconnecting Precatalyst Reconstruction, Long Range Order, Buffer-Binding, Morphology, Mass Transport, and Operation Temperature

“…However, at higher current densities, such limitations can inhibit the OER. [11,12,[41][42][43][44] Mass transport limitations can arise from insufficient electron transport or proton transport (as well as oxygen bubble detachment which is not discussed herein). Recently, it has been proven by in-situ conductivity measurements that electron transport is not a limiting factor.…”

“…Due to the mass transport limitations and inferior kinetics of the OER in near-neutral media compared to a strongly alkaline and acidic one, it is challenging to achieve high current densities at reasonable overpotentials. [14,47] Taking our best catalysts (CoBP-Bi) and considering our deduced concepts and previous reports, [48][49][50][51] we performed the following optimisations of our system to meet this challenge:…”

“…[4,47,52,53] In general, these results show that the gap between near-neutral and strongly alkaline and acidic OER is likely to decrease at elevated temperatures, as those temperatures partly compensate the proton transport disadvantage of buffers compared to hydroxide and protons. [51,54] Furthermore, the solution resistance is decreased (Figure S28c, Supporting Information) and the autoprotolysis of water is enhanced. [55] Long-term stability at higher potentials is a critical issue, as, in near-neutral media, cobalt based catalysts rely on a self-healing mechanism, which prevents complete dissolution of the catalyst by continuous redeposition (but see also ref.…”