How changes in interfacial pH lead to new voltammetric features: the case of the electrochemical oxidation of hydrazine

Arulrajan, Antony C.; Renault, Christophe; Lai, Stanley C. S.

doi:10.1039/c8cp01835a

Cited by 23 publications

(20 citation statements)

References 36 publications

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“…This suggests that a higher peroxide selectivity might be achieved in acid if the electrode surface can be made basic (proton deficient), so that surface peroxides can remain deprotonated and stay charged for kinetics engineering. 40,41 This will shed some light on the holistic design of electrocatalytic interfaces for highly selective peroxide synthesis.…”

Section: Identifying Key Factors For Peroxide Selectivitymentioning

confidence: 99%

Highly Selective Hydrogen Peroxide Electrosynthesis on Carbon: In Situ Interface Engineering with Surfactants

Wang

et al. 2020

Chem

194

130

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Wu et al. demonstrate that a >95% H 2 O 2 selectivity can simply be achieved in an electrosynthesis by using a positively charged surfactant on metal-free carbon electrode without needing sophisticated material design. Under the oxygen reduction reaction, the positively charged promoter pulls off adsorbed peroxide as formed, promoting the release of peroxide while protecting carbon surface from corrosion. It works well with surface carboxylates with weak binding, whereas carbonyl groups hold on to peroxides strongly and thus hinder the desorption and release.

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Section: Identifying Key Factors For Peroxide Selectivitymentioning

confidence: 99%

Highly Selective Hydrogen Peroxide Electrosynthesis on Carbon: In Situ Interface Engineering with Surfactants

Wang

et al. 2020

Chem

194

130

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“…This phenomenon was also used to explain the appearance of a second wave in the CV for hydrazine (also a PCET process) as the buffer capacity of the system was decreased. 35 Furthermore, as quinones can also catalyze ORR 36,37 and ORR itself consumes protons, the presence of oxygen may also lead to additional local pH increases along with contribution of an ORR faradaic signal to the quinone response. 29 ORR-induced pH changes are either neglected in the interpretation of PCET in unbuffered solutions or circumvented by deaerating the solution.…”

Section: ■ Introductionmentioning

confidence: 99%

Deconvoluting Surface-Bound Quinone Proton Coupled Electron Transfer in Unbuffered Solutions: Toward a Universal Voltammetric pH Electrode

et al. 2018

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While quinone proton coupled electron transfer (PCET) under buffered conditions is well understood, the situation is more complicated in unbuffered aqueous solutions. With a view to producing a quinone-based voltammetric pH electrode that can function universally in both buffered and unbuffered solutions by following a twoelectron (2e − )/two-proton (2H + ) Nernstian pathway over a wide pH range, the voltammetric response of strongly electronically coupled surface-bound quinones, directly integrated into a boron-doped diamond (BDD) electrode, is investigated. A laser ablation process enables integration of quinones into the BDD electrode surface with a high pK a1 (first protonation state) and with controllable, very low surface coverages (as low as 2 orders of magnitude below monolayer coverage). Under buffered conditions, one wave results for all pH values, and the 2e − /2H + pathway is followed across the entire pH range. The measured ET rate constant values, from Laviron analysis, are also high, indicative of fast ET pathways. Under unbuffered conditions, one wave is again observed for all pH values; however, deviations from the buffered 2e − /2H + behavior are seen in the neutral region (pH 6−8). While 2e − /2H + transfer is maintained at all times, we attribute the observed deviation to local pH changes caused by the consumption and generation of protons at the electrode surface during the redox electrochemistry of the quinone. The associated proton fluxes generated at such sparse surface coverages are thought to be sufficiently high enough to prevent ET from occurring exclusively via a proton-independent route. By reducing surface coverage (down to ∼4 × 10 −12 mol cm −2 ; the limit of our laser ablation process) local pH changes can be reduced but are not eradicated completely. By moving to a pulsed voltammetric technique, where for each potential step protons consumed at the electrode are immediately replaced, it is possible, provided the surface coverage is low enough, to obtain a Nernstian 2e − /2H + response across a wide pH range in unbuffered solution.

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“…4.5 nA) on the cyclic voltammogram of the Pt UME is attributed to a local change of pH at the surface of the electrode when hydrazine is oxidized. Indeed, the products of hydrazine oxidation are nitrogen and protons that will locally acidify the solution causing a shift of the apparent standard potential [43]. We verified this point by fixing the pH with increasing concentrations of NaOH and observing the complete disappearance of the intermediate plateau when the concentration of NaOH is about five times larger than the concentration of hydrazine ( Figure S1 in SI).…”

Section: Kinetics Of Hydrazine Oxidation On Pt Ume Vs C-fiber Umementioning

confidence: 65%

Detection of individual conducting graphene nanoplatelet by electro-catalytic depression

Deng

Maroun

Dick

et al. 2020

Electrochimica Acta

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We report a strategy to electrochemically detect individual conducting particles colliding with an ultra-microelectrode (UME). This method, called "electro-catalytic depression" (ECD), enables the detection of particles that are electrically conducting but catalytically inert, such as carbonaceous particles. The ECD method takes advantage of the intrinsic difference in heterogeneous kinetics of electron transfer for a given inner-sphere reaction to block the current at the surface of a particle made of a material having poor catalytic properties compared to the material of the electrode. We showcase this method with the detection of individual graphene nanoplatelets (GNPs) of few µm long and 15 nm thick. GNPs block the oxidation of hydrazine on a 5 µm radius Pt UME. We studied the influence of the potential on the current transient produced by individual GNP stochastically colliding on the UME. We evidence that, under 0.1 V vs AgAgCl 3.4 M KCl, electrically conducting GNPs produce discrete stair-shaped drops of current (negative steps) similar to the signal obtained with insulating particles like polystyrene beads. We show how the analysis of a "blocking-type" signal originally developed for insulating beads can be extended to the detection of conducting particles. However, at high potentials (> 0.1 V), where hydrazine oxidation occurs on the GNP, the kinetic difference between GNP and Pt decreases, leading to the decrease of both average and median current step size and the appearance of positive steps. The frequency of collision versus the concentration of GNP and the bias potential are discussed.

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How changes in interfacial pH lead to new voltammetric features: the case of the electrochemical oxidation of hydrazine

Abstract: The electrochemical oxidation of hydrazine was investigated in strongly and weakly pH buffered solutions to reveal the role of buffer capacity in proton–electron transfer redox reactions.

Cited by 23 publications

References 36 publications

Highly Selective Hydrogen Peroxide Electrosynthesis on Carbon: In Situ Interface Engineering with Surfactants

Highly Selective Hydrogen Peroxide Electrosynthesis on Carbon: In Situ Interface Engineering with Surfactants

Deconvoluting Surface-Bound Quinone Proton Coupled Electron Transfer in Unbuffered Solutions: Toward a Universal Voltammetric pH Electrode

Detection of individual conducting graphene nanoplatelet by electro-catalytic depression

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