Rotating Disk Electrode Research Articles

Efficient photocatalytic molecular oxygen activation by TTF-based heterojunction for water purification

Tetrathiafulvalene (TTF), one of the well-known organic photoelectric materials, was served as active sites to accelerate the activation of molecular oxygen to degrade organic pollutants. Herein, a kind of Z-scheme heterojunction photocatalysis was constructed based on g-C3N4 and TTF. According to the experimental results, the mechanism of Z-scheme heterojunction was supported, in which photogenerated electrons transferred from g-C3N4 to TTF. More importantly, TTF on the catalyst surface could serve not only as electron donor, but also as the terminal active site to transfer photoexcited electrons to adsorbed oxygen molecules, producing mass of ⋅O2–. Meanwhile, the activation rate constant of TCN-5 for RhB was 0.0624 min−1, which was 10 and 5 times of g-C3N4 and TTF, respectively. In addition, the results of EPR spectra, rotating disk electrode measurement and molecular oxygen activation measurement also demonstrated that this catalyst was energetically favorable to generate ⋅O2– through the single-electron reduction pathway of molecular oxygen. Finally, four possible photodegradation routes for RhB were proposed based on the results of HPLC-MS. This work provides a new insight on the application of organic photoelectric materials in the purification of wastewater by the molecular oxygen activation.

Nickel-hydroxide decorated trimanganese-tetroxide nanorods supported on graphene as bifunctional electrocatalyst for metal–air batteries

Manganese oxide, such as Mn3O4, is one of promising material as electrocatalyst in air–cathode for metal–air battery due to low cost, high catalytic activity and good stability. Although pure Mn3O4 material exhibits excellent catalytic activity to ORR, it is severely limited by its intrinsically low conductivity and high over-potential toward OER. In this work, the hybrid materials of nickel-hydroxide-decorated nanorods of trimanganese-tetroxide supported on reduced-graphene have been prepared by one-step hydrothermal method. The composite materials are used as bifunctional cathode catalysts to ORR/OER, and investigated by the technologies of rotating disk electrode and metal–air batteries. The results indicate that the hybrid material of Mn-Ni/rGO use as catalyst in air–cathode for Al/Zn–air battery has good catalytic activity. Based on analysis of scanning electron microscope and X-ray photoelectron spectroscopy, the composite material shows good performance owing to the improvement of conductivity supported on graphene, more Mn4+ on the surface of hybrid material, the coexistence of Mn3+/Mn4+ redox couple, and the synergism between nickel-hydroxide and graphene.

Enhanced Mass Activity and Durability of Bimetallic Pt-Pd Nanoparticles on Sulfated-Zirconia-Doped Graphene Nanoplates for Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cell Applications.

Developing highly active and durable Pt-based electrocatalysts is crucial for polymer electrolyte membrane fuel cells. This study focuses on the performance of oxygen reduction reaction (ORR) electrocatalysts composed of Pt-Pd alloy nanoparticles on graphene nanoplates (GNPs) anchored with sulfated zirconia nanoparticles. The results of field emission scanning electron microscopy and transmission electron microscopy showed that Pt-Pd and S-ZrO2 are well dispersed on the surface of the GNPs. X-ray diffraction revealed that the S-ZrO2 and Pt-Pd alloy coexist in the Pt-Pd/S-ZrO2-GNP nanocomposites without affecting the crystalline lattice of Pt and the graphitic structure of the GNPs. To evaluate the electrochemical activity and reaction kinetics for ORR, we performed cyclic voltammetry, rotating disc electrode, and EIS experiments in acidic solutions at room temperature. The findings showed that Pt-Pd/S-ZrO2-GNPs exhibited a better ORR performance than the Pt-Pd catalyst on the unsulfated ZrO2-GNP support and with Pt on S-ZrO2-GNPs and commercial Pt/C.

Insights into the electrochemical oxidation selectivity of hydroxymethylfurfural over humin-layered Au nanoparticles

Au nanoparticle catalysts are promising electrocatalysts for biomass upgrading. Starting from a pristine Au electrode, herein we demonstrate a simple route for the electrochemical preparation of Au NPs supported on thin layers of humin (Au/H). Utilizing an oxidized Au surface as a precursor, these electrocatalytic structures are formed upon reduction of 5-hydroxymethylfurfural (HMF) in alkaline media while performing a potential sweep. We subsequently utilize this Au/H structure for the electrochemical oxidation of ethanol and HMF in a rotating disk electrode (RDE) configuration and perform additional analysis via electrochemical surface-enhanced Raman Scattering (SERS). The RDE test reveals Au/H has different reaction kinetics towards alcohol and aldehyde functional groups, enabling a mechanistic understanding of the reaction pathway for HMF oxidation. The SERS experiment identifies the favorable reduction pathway from Au2O3 to gold, suggesting the possible active site on this catalyst for HMF oxidation.

Tributyl(hexyl)phosphonium chloride as a new leveler for microvia copper superconformal electronic plating

A phosphorus-containing new compound of tributyl(hexyl)phosphonium chloride (TBHP), but not the commonly used nitrogen-containing heterocycles and quaternary ammonium salts, is successfully applied for the superconformal copper filling of microvia in acid sulfate electroplating bath for the application of electronic industry. The molecular interaction mechanisms of TBHP combined with suppressor (polyethylene glycol, PEG) and accelerator (bis-(sodium sulfopropyl)-disulfide, SPS) are investigated in detail. Galvanostatic measurements at platinum rotation disk electrode indicate that the leveler of TBHP among with the suppressor and accelerator behaves the key characters of inhibition and convection-dependent adsorption during copper ions electroreduction for the bottom-up filling of microvia. Cyclic voltammetry measurements and in-situ FTIR spectroscopy further reveal that TBHP synergistically interacts with the suppressor to inhibit copper ions electroreduction at the mouth of microvia; while TBHP competes for adsorption with the accelerator, behaving as TBHP gradually replaced by the accelerator at the bottom. Based on the sufficient theoretical supports, the practical copper electroplating is conducted for the verification of microvia void free filling. In the developed novel copper plating formula containing TBHP, PEG and SPS, the void free filling is successfully achieved and the filling percentage (FP) is high in 95.5%.

Metal–organic framework–derived trimetallic particles encapsulated by ultrathin nitrogen-doped carbon nanosheets on a network of nitrogen-doped carbon nanotubes as bifunctional catalysts for rechargeable zinc–air batteries

Economical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts with high activity aimed at replacing precious metal catalysts for rechargeable zinc-air batteries (ZABs) must be developed. In this study, a multiple hierarchical-structural material is developed using a facile dielectric barrier discharge (DBD) plasma surface treatment, solvothermal reaction, and high-temperature carbonization strategy. This strategy allows for the construction of nanosheets using nitrogen-doped carbon (NC) material-encapsulated ternary CoNiFe alloy nanoparticles (NPs) on a network of NC nanotubes (NCNTs), denoted as CoNiFe–NC@p–NCNTs. Precisely, the presence of abundant CoNiFe alloy NPs and the formation of M–N–C active sites created by transition metals (cobalt, nickel, and iron) coupled with NC can provide superior OER/ORR bifunctional properties. Moreover, the prepared NC layers with a multilevel pore structure contribute to a larger specific surface area, exposing numerous active sites and enhancing the uniformity of electron and mass movement. The CoNiFe0.08–NC@p–NCNTs show remarkable dual functionality for electrochemical oxygen reactions (ORR half-wave potential of 0.811 V, limiting current density of 5.73 mA cm−2 measured with a rotating disk electrode at a rotation speed of 1600 rpm, and OER overpotential of 351 mV at 10 mA cm−2), which demonstrates similar ORR performance to 20 wt% Pt/C and better OER performance than the commercial RuO2. A liquid ZAB prepared using the proposed material has excellent bifunctionality with an open-circuit voltage of 1.450 V and long-term cycling stability of 230 h@10 mA cm−2.

An all-metallic nanovesicle for hydrogen oxidation

Abstract Vesicle, a microscopic unit that encloses a volume with an ultrathin wall, is ubiquitous in biomaterials. However, it remains a huge challenge to create its inorganic metal-based artificial counterparts. Here, inspired by the formation of biological vesicles, we proposed a novel biomimetic-strategy to curling the ultrathin nanosheets into nanovesicles, which was driven by the interfacial strain. Trapped by the interfacial strain between initially formed substrate Rh layer and subsequently formed RhRu overlayer, the nanosheet begins to deform to release a certain strain. Density functional theory (DFT) calculations reveal that the Ru atoms make the curling of nanosheet more favorable in thermodynamics. Owing to the unique vesicular structure, the RhRu nanovesicles/C displays excellent hydrogen oxidation reaction (HOR) activity and stability, which has been proven by both the experiments and DFT calculations. Specifically, the HOR mass activity of RhRu nanovesicles/C are 7.52 A mg(Rh+Ru)−1 at an overpotential of 50 mV in rotating disk electrode (RDE) level; this is 24.19 times higher than that of commercial Pt/C (0.31 mA mgPt−1). Moreover, the hydroxide exchange membrane fuel cell (HEMFCs) with RhRu nanovesicles/C displays a peak power density of 1.62 W cm−2 in H2-O2 condition, much better than that of commercial Pt/C (1.18 W cm−2). This work creates a new biomimetic strategy to synthesize inorganic nanomaterials, paving out a pathway for designing catalytic reactors.

Parameter estimations from SARS-CoV-2 electrochemical interactions

Electrochemical pathogen sensing has gathered limelight for its effective and ultrafast detection capabilities. More recently, several electrochemical sensors were developed to counter the increasing testing requirement for the 2019 coronavirus disease (COVID-19) diagnosis. One such sensor developed was the Ultrafast COVID-19 (UFC-19) diagnostic sensor which could detect the SARS-CoV-2 spike protein in saliva samples. Although UFC-19 was established in literature to sense SARS-CoV-2 in saliva samples, the factors causing such an interaction or parameters to model such an interaction are yet to be studied in detail. In this work, an attempt has been made to electrochemically characterize the interactions at the interface by employing cyclic and linear sweep voltammetry on a rotating disk electrode setup. As a result, electrochemical parameters were calculated using chemical and electrochemical principles. The electrochemical surface area, electrode surface coverage, diffusion coefficient, reaction order with respect to SARS-CoV-2 whole virus, electron transfer coefficient have been estimated providing additional insights into the events occurring at the electrical double layer. The reaction order for the interaction was reckoned to be 0.7 confirming a non-elementary, multi-step process occurring at the interface. Theoretical and experimental calculations confirm higher hydroxide ion accumulation at the interface in the presence of SARS-CoV-2 whole virus. Results from this work lay the foundation for developing models for electrochemical SARS-CoV-2 interaction and possible extension toward other pathogenic viruses.

Revealing cellular (poly)sulphide storage in electrochemically active sulphide oxidising bacteria using rotating disc electrodes

Sulphide oxidising bacteria (SOB) have the potential to be used for bioelectrochemical removal, i.e. oxidation, of sulphide from waste streams. In anaerobic conditions, SOB are able to spatially separate sulphide removal and terminal electron transfer to an electrode and act as a sulphide shuttle. However, it is not fully understood how SOB anaerobically remove sulphide and store charge equivalents, and where in this process sulphur is formed. Therefore, the redox behaviour of sulphide shuttling SOB was investigated at haloalkaline conditions using a glassy carbon rotating disc electrode (RDE) and cyclic voltammetry. Voltammograms of SOB in the absence and presence of sulphide were compared to voltammograms of abiotic sulphur species solutions. Polysulphide and sulphide showed different redox behaviour, with distinct potentials for oxidation of > −0.3 V (vs. Ag/AgCl) for polysulphide and > −0.1 V for sulphide. Comparing biotic to abiotic experiments lead to the hypothesis that SOB formed polysulphides during anaerobic sulphide removal, which stayed sorbed to the cells. With this study, further steps were taken in elucidating the mechanisms of sulphide shuttling by SOB.

The Electrocatalytic Activity of Au Electrodes Changes Significantly in Various Na+/K+ Supporting Electrolyte Mixtures

The potential of maximum entropy (PME) is an indicator of extreme disorder at the electrode/electrolyte interface and can predict changes in catalytic activity within electrolytes of varying compositions. The laser‐induced current transient technique is employed to evaluate the PME for Au polycrystalline (Aupc) electrodes immersed in Ar‐saturated cation electrolyte mixtures containing potassium and sodium ions at pH = 8. Five cation ratios (0.5 M K2SO4:0.5 M Na2SO4 = 0:1, 0.25:0.75, 0.5:0.5, 0.75:0.25, and 1:0) are explored, considering earlier studies that unveil cation‐dependent shifts at near‐neutral pH. Moreover, for all electrolyte compositions, electrochemical impedance spectroscopy is utilized to determine the double‐layer capacitance (CDL), the minimum of which should be close to the potential of zero charge (PZC). By correlating cation molar ratios with the PMEs and PZCs, the impact on the model oxygen reduction reaction (ORR) activity, assessed via the rotating disk electrode method, is analyzed. The results demonstrate a linear relationship between electrolyte cation mixtures and PME, while ORR activity exhibits an exponential trend. This observation validates the PME–activity link hypothesis, underscoring electrolyte components’ pivotal role in tailoring interfacial properties for electrocatalytic systems. These findings introduce a new degree of freedom for designing optimal electrocatalytic systems by adjusting various electrolyte components.

One‐Pot Synthesis of Carbon‐Supported Pd Nanoparticles with Ni and Carbon Matrix Protection for Durable Alkaline Hydrogen Oxidation Reaction

Protecting nanoparticles with a carbon matrix can enhance the durability of the catalysts in alkaline fuel cells (AFC) and is well‐documented. While others have tried complex syntheses to produce small nanoparticle catalysts, in this work, in order to scale‐up batches of 15 g or more, carbon‐cap (or carbon‐coating) protected Vulcan XC72‐supported Pd‐Ni (1‐2) nanoparticles (Pd‐Niacc/C) were successfully synthesized via a one‐step dry‐synthesis process. This catalyst was compared with a commercial Pd‐Ni/Vulcan XC72 material (PdNi/C, Premetek) in terms of hydrogen oxidation reaction (HOR) activity and stability. To produce less ordered carbon caps (versus graphite/graphene), a low‐temperature heat‐treatment (below 500°C) was used, resulting in Pd‐Niacc/C of unique electrochemical properties: easily electrochemically activated, this catalyst outperforms PdNi/C for alkaline HOR and proves more durable under highly oxidizing accelerated stress test (AST) conditions. Identical location transmission electron microscopy (ILTEM), X‐ray photoelectron spectroscopy (XPS) and rotating disk electrode (RDE) measurements demonstrate how the Ni‐rich surface plays an important role in HOR activity for both PdNi/C and PdNiacc/C and that the protective carbon‐coating of the latter ensures better durability of performance and better resistance to materials degradation.

Pt/C Electrocatalysts with High Pt Density: A Case Study on Oxygen Reduction Performance from Rotating Disk Electrode to Membrane Electrode Assembly

Pt/C Electrocatalysts with High Pt Density: A Case Study on Oxygen Reduction Performance from Rotating Disk Electrode to Membrane Electrode Assembly

Electrochemical oxidation of glucose in alkaline environment—A comparative study of Ni and Au electrodes

The glucose oxidation reaction (GOR) was studied on Au and Ni electrodes by cyclic voltammetry (CV), rotating disk electrode (RDE) measurements coupled with Koutecky–Levich analysis, Differential Electrochemical Mass Spectrometry (DEMS), in situ Fourier Transform Infrared spectroscopy (FTIRS) and High Performance Liquid Chromatography (HPLC) analysis of the reaction products after electrolysis in potentiostatic mode under continuous flow conditions. This study allowed to identify the reaction products and propose tentative reaction mechanisms. On gold, glucose is adsorbed on metallic sites through its anomeric function (C1) resulting in the formation of gluconate as the main GOR product at potentials close to 0.6 V vs. RHE, with a selectivity towards gluconate close to 100% and a projected faradaic efficiency of ca. 70%. The conversion rate is rather low, close to 20%, due to poisoning of the surface, leading to a strong deactivation. At potentials above 0.7 V vs. RHE, the selectivity towards gluconate decreases and non-selective GOR oxidation proceeds through CC bond cleavage. On nickel, the GOR occurs at high potentials (close to 1.2 V vs. RHE) on Ni(OH)2 and NiOOH sites, and proceeds through C1C2 bond breaking, resulting in arabinose and formate. At higher potentials, the selectivity towards arabinose decreases, formate being the main reaction product.

Boron and Fluorine Co‐Doped Graphene/Few‐Walled Carbon Nanotube Composite as Highly Active Electrocatalyst for Oxygen Reduction Reaction

Functionalization of nanocarbon materials with heteroatoms is of paramount interest as doping of carbon with electron withdrawing groups results in change of electrochemical properties of the potential catalyst. Adding fluorine, as the most electronegative element into the doping process next to boron is expected to have significant effect on the design of novel nanocarbon‐based electrocatalysts. In this paper boron and fluorine co‐doped reduced graphene oxide/few‐walled carbon nanotube (BF‐rGO/FWCNT) catalyst are synthesized via simple and low‐cost direct pyrolysis method using boron trifluoride diethyl etherate (BTDE). Composition analysis confirmed that boron and fluorine have been grafted onto the carbon support. Rotating disk electrode (RDE) measurements revealed that BF‐rGO/FWCNT has remarkable electrocatalytic activity toward the oxygen reduction reaction (ORR) both in alkaline and acid media. The onset potential of the best BF‐rGO/FWCNT catalyst was 50 mV more positive in alkaline and 600 mV more positive in acidic media compared with un‐doped rGO/FWCNT. The half‐wave potential was 100 mV more positive in alkaline media and 700 mV more positive in acidic media in comparison with un‐doped rGO/FWCNT.

Encapsulated cementite enhances catalytic performance of carbon nanotubes for oxygen reduction reaction

Nonprecious-metal-based materials show great potential to be highly efficient catalysts for oxygen reduction reaction (ORR). There is still room for improvement in the performances of nonprecious-metal-based catalysts for ORR. In this paper, we investigated the catalytic performances of N-doped carbon nanotubes (CNTs) with encapsulated cementite (Fe3C@CNT) for ORR. The encapsulation structure was confirmed by scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analyses. The catalytic performances of Fe3C@CNT for ORR were investigated by cyclic voltammetry, linear sweep voltammetry, Tafel analysis, rotating disk electrode, and rotating ring-disk electrode tests. The results showed that both the onset potential and half-wave potential of Fe3C@CNT-catalyzed ORR were 60 mV higher than those of 20 wt% Pt/C catalyst. Fe3C@CNT catalyzed ORR mainly happened through a four-electron pathway. The long-time running stability of the Fe3C@CNT was also superior to that of the 20 wt% Pt/C catalyst. The eutectic layers between the CNTs and cementite enhanced the electron transfer from the inner-layer CNT to the surface-layer N-doped CNT. Calculations revealed that the iron and carbon in the cementite were in positive and negative electronic states, respectively. The encapsulated cementite promoted the formation of equipotential circles on the surface-layer CNT, which greatly enhanced the catalytic performance of the Fe3C@CNT for ORR. N-doped CNTs with encapsulated cementite show great potential to be high-performance catalysts for ORR.

Impact of Heat Treatment on the Oxygen Reduction Reaction Performance of PtCo/C(N) Electrocatalyst in PEM Fuel Cell

AbstractThe synthesis of efficient and stable Pt alloy catalysts is a major challenge for the commercialization of PEMFC. Herein, we report a PtCo/C(N) electrocatalyst prepared by Na2CO3‐assisted urea liquid‐phase deposition strategy as an efficient cathodic oxygen reduction reaction electrocatalyst, and test its activity and stability in a rotating disc electrode and a single‐cell. The membrane electrode prepared with PtCo/C(N)‐800 °C catalyst has an output voltage of 0.652 V at 2 A/cm2 and a maximum power density of 1.501 W/cm2, which are 36 mV and 81 W/cm2 higher than those of commercial Pt/C catalyst, respectively. In addition, the mass activity and half‐wave potential of PtCo/C(N)‐800 °C are 2.44 times and 50 mV higher than those of commercial Pt/C, respectively. After 5000 voltammetric cycles, its mass activity and half‐wave potential only lose 35 A/gPt and 9 mV, respectively. XPS results show that the binding energy of Pt 4f is positively shifted relative to Pt/C‐TKK, and the d‐band center of Pt decreases, leading to weak chemical interaction between the oxygen‐containing intermediate and the surface of the electrocatalyst, which is conducive to the improvement of the ORR activity and stability of the catalyst.

Enhancing Intrinsic Electrocatalytic Activity of Pt/C Nanoparticles for Ox-ygen Reduction Reaction in Acidic Media by Microwave-Assisted Synthesis

Abstract: This study is focused on the enhancement of the intrinsic electrocatalytic activity of Pt nanoparticles supported on C (Pt/C NPs) towards Oxygen Reduction Reaction (ORR) in acidic media. The goal was to investigate the effect of microwave-assisted synthesis on the electrocatalytic perfor-mance of Pt/C NPs towards ORR. Thus, Pt/C NPs were synthesized using a microwave-assisted method and by a conventional heating method; structural and morphological characteristics were an-alyzed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Electrochemical studies were performed using the rotating disk electrode technique to evaluate the ORR performance. Microwave-assisted synthesis produced Pt/C NPs with a smaller particle size (6.3 ± 0.2 nm) than con-ventionally synthesized nanoparticles (8.6 ± 0.3 nm). Electrochemical analysis showed that the micro-wave-synthesized Pt/C NPs exhibited higher mass activity (4.6 ± 0.8 mA･g-1Pt) for ORR compared to conventionally synthesized nanoparticles (1.9 ± 0.4 mA･mA･g-1Pt). These results demonstrate that microwave-assisted synthesis enhances the intrinsic electrocatalytic activity of Pt/C NPs for ORR in acidic media. These findings have important implications for the development of efficient electrocat-alysts for fuel cell applications. Background: The synthesis and characterization of platinum nanoparticles on C are crucial for ad-vancing electrocatalysis, particularly in the context of potential applications in fuel cells. This study builds on previous research, focusing on two distinct synthesis methods to enhance our understanding of their impact on nanoparticle properties and electrocatalytic performance. Objective: To investigate the synthesis efficiency, structural characteristics, and electrocatalytic activ-ities of platinum nanoparticles on C using microwave-assisted heating and conventional synthesis re-actor heating. The objective is to discern any significant differences in particle size, structure, and electrocatalytic performance between the two synthesis methods. method: The synthesis involved a comparative analysis of platinum nanoparticles using microwave-assisted and conventional heating methods. Chemical composition analysis verified the synthesis efficiency, and structural and morphological characterizations were performed using X-ray Diffraction and Transmission Electron Microscopy. Electrochemical studies employed the rotating disk electrode technique, with activation and evaluation conducted through cyclic voltammetry, and the oxygen reduction reaction studied via linear sweep voltammetry in an acidic media (0.5 mol⋅L-1 H2SO4). Methods: The synthesis involved a comparative analysis of platinum nanoparticles using microwave-assisted and conventional heating methods. Chemical composition analysis verified the synthesis ef-ficiency, and structural and morphological characterizations were performed using X-ray Diffraction and Transmission Electron Microscopy. Electrochemical studies employed the rotating disk electrode technique, with activation and evaluation conducted through cyclic voltammetry, and the oxygen re-duction reaction studied via linear sweep voltammetry in an acidic media (0.5 mol⋅L-1 H2SO4). Results: Well-supported platinum nanoparticles with a face-centered cubic structure were obtained on C using both synthesis methods. However, microwave-synthesized particles (6.3 ± 0.2 nm) exhibited a smaller size compared to conventionally synthesized particles (8.6 ± 0.3 nm). Electrochemical as-sessment revealed superior mass activity for microwave-synthesized material (4.6 ± 0.8 mA･g-1Pt), outperforming commercial Pt nanoparticles (3.0 ± 0.3 mA･g-1Pt) and conventionally synthesized ma-terial (1.9 ± 0.4 mA･mA･g-1Pt). Conclusion: This study concludes that microwave-assisted synthesis yields platinum nanoparticles on C with enhanced electrocatalytic performance, as evidenced by the smaller particle size and superior mass activity compared to conventionally synthesized material and commercial Pt nanoparticles. These findings highlight the potential of microwave-synthesized Pt nanoparticles for applications in fuel cells.

Unravelling the Mechanism of Electrochemically Induced Sol-Gel Depositions: pH Profiles Near Electrode and Influence on Film Growth

Abstract Electrochemically induced sol-gel depositions have become a widespread, versatile method for fabricating hybrid and nanostructured oxides on conductive substrates. The process is based on the buildup of electrochemically generated OH- in the diffusion layer near the electrode surface. For the electrodeposition of silica thin films, these OH- ions catalyze the gelation of a kinetically stable precursor solution, thereby resulting in an electrochemically controlled process. The control of the diffusion layer has proven pivotal to depositing thin films while preventing the formation of aggregated by-products deeper in the solution. In this work, the silica sol-gel reactions and electrochemical OH- generation were critically analyzed and described to gain insight into the deposition mechanism. A general model is proposed that predicts the pH profile during both stationary and rotating disk electrode depositions under different conditions (i.e., current densities, times, and rotation rates). This model provides insights into the reactive zones where gelation occurs, and explains typical phenomena observed during deposition such as the dependence of film growth rates and aggregate formation on the deposition conditions. The insights and expressions obtained in this work are invaluable when designing future experiments using novel chemistries or setups.

Screening reversal tolerance through rotating disc electrode studies

Anode reversal is a detrimental phenomenon that occurs in proton exchange membrane fuel cells (PEMFCs) when the anode is subject to fuel starvation, leading to irreversible damage. This is a critical issue for the commercialization of PEMFCs. However, the development of more robust anode catalysts has been limited by the need for membrane electrode assembly (MEA)-level testing, which is costly and time-consuming. Here, we propose two accelerated stress test (AST) protocols based on widely available rotating disc electrode (RDE) methods to determine their suitability for screening anode catalysts and predicting MEA-level durability. One method is based on a carbon corrosion (cc) voltage cycling protocol between 1.0 and 1.5 V vs. RHE, while the other is a chronopotentiometry (cp) method. We evaluate three model catalysts (Pt30, Pt50, and Pt70) at the MEA-level through standard reversal testing and at the RDE-level using the two AST protocols (RDE-cc and RDE-cp). We find that both RDE-level methods can reliably predict MEA-level anode durability, and can be used by materials scientists to screen the relative durability of new anode catalysts. Our results also suggest Pt70 is a promising candidate for anode reversal tolerant PEMFCs, as it shows superior durability under both MEA-level and RDE-level tests.

Combining a Commercial Mixer with a Wall-Tube Electrode Allows the Arbitrary Control of Concentrations in Protein Film Electrochemistry.

Protein film electrochemistry is a technique in which an enzyme is immobilized on an electrode in a configuration that allows following the changes in turnover frequency as a response to changes in the experimental conditions. Insights into the reactivity of the enzyme can be obtained by quantitatively modeling such responses. As a consequence, the more the technique allows flexibility in changing conditions, the more useful it becomes. The most commonly used setup, based on the rotating disc electrode, allows easy stepwise increases in the concentration of nongaseous substrates, or exposure to constant concentration of dissolved gas, but does not permit to easily decrease the concentration of nongaseous substrates, or to change the concentration of dissolved gas in a stepwise fashion. To overcome the limitation by mass transport of the substrate toward the electrode when working with fast enzymes, we have designed another kind of electrochemical cell based on the wall-tube electrode (WTE). We demonstrate here that by using a system combining two syringe pumps, a commercial mixer, and the WTE, it is possible to change the concentration of species in a stepwise fashion in all directions, opening new possibilities to study redox enzymes. As a proof of concept, this device was applied to the study of the electrochemical response of the cytochrome c nitrite reductase of Desulfovibrio desulfuricans.