High Anodic Potentials Research Articles

Confining Flat Ru Islands into TiO2 Lattice with the Coexisting Ru-O-Ti and Ru-Ti Bonds for Ultra-Stable Hydrogen Evolution at Amperometric Current Density and Hydrogen Oxidation at High Potential.

Effective hydrogen evolution reaction (HER) under high current density and enhanced hydrogen oxidation reaction (HOR) over a wide potential range remain challenges for Ru-based electrocatalysts because its strong affinity to the adsorbed hydroxyl (OHad) inhibits the supply of the adsorbed hydrogen (Had). Herein, the coexisting RuOTi and Ru-Ti bonds are constructed by taking TiO2 crystal confined flat-Ru clusters (F-Ru@TiO2) to cope with above-mentioned obstacles. The different electronegativity (χTi = 1.54 < χRu = 2.20 < χO = 3.44) can endow Ti sites in RuOTi bonds with more positive charge and stabilize Ru atoms of RuTi bonds with the low-valence. The strength of Ru-OHad is then weakened by the oxophilicity of positively charged Ti atom in Ru-O-Ti bonds and the stronger Ti-OHad bond could release active Ru sites, especially for low-valence Ru in RuTi bonds, to serve as exclusive Had sites. As expected, F-Ru@TiO2 shows a low HER overpotential of 74 mV at 1000mA cm-2 and an ultrahigh mass activity of 3155A gRu -1 for HOR. More importantly, F-Ru@TiO2 can tolerate the HER current density of 1000mA cm-2 for 100h and the high anodic potential for HOR up to 0.5V versus RHE.

A facile synthesis of N-doped carbon encapsulated multimetallic carbonitride as a robust electrocatalyst for oxygen evolution reaction

Electrocatalytic water splitting is a promising solution for generating clean hydrogen. Transition metal compounds are among the most extensively investigated catalysts developed to date for water oxidation in alkaline media, a process also known as the oxygen evolution reaction (OER). However, the application of these catalysts was constrained by insufficient stability arising from surface oxidation and metal dissolution under high OER potential. In this work, we developed a facile approach using urea-based gel as the precursor of preparing a series of multimetallic carbonitride particles which were encapsulated by N-doped carbon (NC). In particular, (MoCoFeNiZr)CN@NC core–shell structure delivered a low overpotential of 246 mV at a current density of 10 mA cm−2 in 1 M KOH during OER. Importantly, operando differential electrochemical mass spectrometry (DEMS), together with multiple microscopic and spectroscopic analyses, indicated that the NC shells effectively maintained the crystalline stability of carbonitride via suppressing the surface reconstruction during catalysis. The highly graphitic NC also demonstrates excellent stability against oxidation. This work shows a promising strategy of stabilizing electrocatalyst at high anodic potential, paving the way for the development of robust electrode materials for energy conversion.

Hydrodynamics and mass transport in an anodic oxidation reactor: Influence of gas evolution and flow path through mesh electrodes

Removal of organic compounds by anodic oxidation requires a sufficiently high rate of mass transport of target compounds to the electrode surface. Since anodic oxidation is often accelerated by the formation of hydroxyl radicals from water oxidation at high anodic potential, the role of oxygen/hydrogen evolution reactions was investigated. Residence time distributions showed that formation of bubbles in zones where fluid velocity was minimal, allowed for strongly improving global hydrodynamics in the reactor. The role of bubbles was also discussed by comparing mass transport coefficients obtained from the limiting current technique to values obtained from kinetics of COD removal during treatment of a model pollutant (phenol). The use of mesh electrodes (with liquid flowing through the electrode) further promoted convection and mass transport of organic compounds compared to plates. However, large bubbles generated at plate electrodes also allowed for convection enhancement in the vicinity of surface of plate electrodes. In both cases, an adverse effect from bubble adhesion was observed because of the decrease in the active surface of electrodes. The mass transport coefficient obtained with the limiting current technique using mesh electrodes was 0.69 10−3 cm/s at 10.8 L/h with a mean velocity of electrolyte past the mesh surface (u¯mesh) of 0.37 cm/s. It decreased to 0.58 10−3 cm/s during the treatment of phenol at the same flow and reached 0.75 10−3 cm/s when increasing the flow to 32.4 L/h. By taking into consideration gas evolution at the surface of electrodes, this study allowed for accurate calibration of an advective – dispersive model with reaction that could be used for sizing such reactors according to the intended application.Abbreviations: Ae, the volumetric surface area (ratio between the geometric volume and the active surface area of the mesh electrodes) (cm−1); CA, aeration by a floor diffuser of fine bubbles and no current at the electrodes; CEP, polarization of the electrodes with a current intensity and no aeration; CW, no electrode polarization and no aeration; COD, chemical oxygen demand (mgO2 L−1);Di, diffusion coefficient of specie i (m2/s); D, dispersion coefficient (cm2 min−1); E(θ), residence time distribution function; EC, electrical energy consumption (kWh gCOD−1);F, Faraday constant (96485C mol−1); HER, hydrogen evolution reaction; IOA, index of agreement;km, mass transport coefficient (m/s); MCE, mineralization current efficiency; ME, model efficiency; OER, oxygen evolution reaction; OH, hydroxyl radical;Ql, liquid flow rate (L/h); rAO: anodic oxidation rate (mol/m−3 s−1); RTD: residence time distribution; ts¯: mean residence time or first moment order; u¯: mean flow velocity (m/s); VT: total volume (L); σ2: variance or second moment order; γ: skewness factor or third moment order; τ: residence time; μ: order moment.

Enhanced performance of Ti–Nb–N film modified 316L stainless steel and Ti bipolar plates for proton exchange membrane water electrolyser

Proton exchange membrane water electrolyser (PEMWE) is crucial for contemporary hydrogen generation technology. However, the corrosion of bipolar plates (BPPs) poses a significant challenge primarily due to the high anodic potential and acidic environments throughout the operation. This study compares the performance of the innovative Ti–Nb–N film modified 316L stainless steel and Ti bipolar plates under simulated PEMWE operating conditions. Interfacial contact resistance (ICR) experimental results confirm that the Ti–Nb–N film significantly reduces the ICR of the modified Ti plates and 316L stainless steel by approximately 77.7% and 91.0% respectively. According to the polarization tests, the Ecorr of the modified 316L stainless steel and Ti plates shows positive shifts, increasing by 318.49 mV and 376.64 mV, respectively. The Ti–Nb–N film modified 316L stainless steel plates are durable up to 1.4 V (vs. Ag/AgCl), while modified Ti plates maintain performance up to 1.8 V (vs. Ag/AgCl).

Impact of metal oxides on the selectivity of NiBi/C catalysts for high-value C-3 products in glycerol electrooxidation reaction

Enhancing the catalytic efficiency and specificity of non-noble Nickel-based catalysts for glycerol electro-oxidation reaction (GEOR) is an ongoing challenge. Recently, metal oxides have attracted attention due to their unique physical properties, such as chemical stability at high anodic potentials, presence of oxygen vacancies, which can significantly influence reaction kinetics and pathways.In this study, we explored the impact of metal oxides CeO2, SnO2, and Sb2O3 • SnO2 (ATO) on the electrochemical performance and product selectivity of NiBi/C and Ni/C catalysts in glycerol electrooxidation (GEOR). The Ni/C-X and NiBi/C-X (X= CeO2, SnO2, and ATO) catalysts were synthesized through a sodium borohydride reduction method at room temperature and comprehensively characterized using various physiochemical and electrochemical techniques.Among the composite support catalysts, Ni and NiBi/C-X, Ni/C-ATO exhibited the highest peak current density, reaching 96 mA cm-2 at 1.50 V vs. RHE. To further assess the catalysts' performance, continuous electrolysis, coupled with HPLC analysis, was conducted to determine product selectivity. Notably, NiBi/C-ATO demonstrated remarkable selectivity, achieving 100 % lactate selectivity under mild conditions. These findings contribute valuable insights into optimizing non-noble Nickel-based catalysts for GEOR, particularly highlighting the promising performance of Ni/C-ATO in terms of selectivity towards valuable products. The DFT calculations provided insight into the synergistic interactions for GEOR over Ni-Ni and Bi-Bi nanoparticles.

Similarities and Differences between Gas Diffusion Layers Used in Proton Exchange Membrane Fuel Cell and Water Electrolysis for Material and Mass Transport.

Proton-exchange membrane fuel cells (PEMFCs) and water electrolysis (PEMWE) are rapidly developing hydrogen energy conversion devices. Catalyst layers and membranes have been studied extensively and reviewed. However, few studies have compared gas diffusion layers (GDLs) in PEMWE and PEMFC. This review compares the differences and similarities between the GDLs of PEMWE and PEMFC in terms of their material and mass transport characteristics. First, the GDL materials are selected based on their working conditions. Carbon materials are prone to rapid corrosion because of the high anode potential of PEMWEs. Consequently, metal materials have emerged as the primary choice for GDLs. Second, the mutual counter-reactions of the two devices result in differences in mass transport limitations. In particular, water flooding and the effects of bubbles are major drawbacks of PEMFCs and PEMWE, respectively; well-designed structures can solve these problems. Imaging techniques and simulations can provide a better understanding of the effects of materials and structures on mass transfer. Finally, it is anticipated that this review will assist research on GDLs of PEMWE and PEMFC.

How to perform corrosion experiments for proton exchange membrane water electrolysis bipolar plates

Ex-situ corrosion experiments are very common to identify the suitability of metallic materials for various applications. While for proton exchange membrane (PEM) fuel cells the US Department of Energy (DoE) gives a clear guidance on how to perform corrosion experiments, no such guidance exists for PEM water electrolyzer (PEMWE) applications. For the latter, much higher anodic potentials (when compared to fuel cells) of up to +2 V vs. RHE must be considered for bipolar plates. Consequently, in aqueous electrolytes oxygen evolution via water splitting takes place in parallel and the two processes corrosion vs. oxygen evolution cannot easily be separated. We herein demonstrate how corrosion experiments for PEMWE applications can be performed and ascribe the contribution of oxygen evolution during such experiments. Together with the shown comprehensive surface analysis of the metallic sample and analysis of the electrolyte via ICP-MS a clear picture of the stability of 316L stainless steel under electrolysis conditions is given. The described method allows both, the evaluation of metals and alloys as well as coatings on different metals for electrolyzer applications.

Unravelling the mechanisms of organic micropollutant removal in bio-electrochemical systems: Insights into sorption, electrochemical degradation, and biodegradation processes

Bio-electrochemical systems (BESs) have recently been proposed as an efficient treatment technology to remove organic micropollutants from water treatment plants. In this study, we aimed to differentiate between sorption, electrochemical transport/degradation, and biodegradation. Using electro-active microorganisms and electrodes, we investigated organic micropollutant removal at environmentally relevant concentrations, clarifying the roles of sorption and electrochemical and biological degradation. The role of anodic biofilms on the removal of 10 relevant organic micropollutants was studied by performing separate sorption experiments on carbon-based electrodes (graphite felt, graphite rod, graphite granules, and granular activated carbon) and electrochemical degradation experiments at two different electrode potentials (−0.3 and 0 V).Granular activated carbon showed the highest sorption of micropollutants; applying a potential to graphite felt electrodes increased organic micropollutant removal. Removal efficiencies >80 % were obtained for all micropollutants at high anode potentials (+0.955 V), indicating that the studied compounds were more susceptible to oxidation than to reduction. All organic micropollutants showed removal when under bio-electrochemical conditions, ranging from low (e.g. metformin, 9.3 %) to exceptionally high removal efficiencies (e.g. sulfamethoxazole, 99.5 %). The lower removal observed under bio-electrochemical conditions when compared to only electrochemical conditions indicated that sorption to the electrode is key to guarantee high electrochemical degradation. The detection of transformation products of chloridazon and metformin indicated that (bio)-electrochemical degradation occurred. This study confirms that BES can treat some organic micropollutants through several mechanisms, which merits further investigation.

Structural and Electronic Factors behind the Electrochemical Stability of 3D-Metal Tungstates under Oxygen Evolution Reaction Conditions.

Transition metal tungstates (TMTs) possess a wolframite-like lattice structure and preferably form via an electrostatic interaction between a divalent transition metal cation (MII) and an oxyanion of tungsten ([WO4]2-). A unit cell of a TMT is primarily composed of two repeating units, [MO6]oh and [WO6]oh, which are held together via several M-μ2-O-W bridging links. The bond character (ionic or covalent) of this bridging unit determines the stability of the lattice and influences the electronic structure of the bulk TMT materials. Recently, TMTs have been successfully employed as an electrode material for various applications, including electrochemical water splitting. Despite the wide electrocatalytic applications of TMTs, the study of the structure-activity correlation and electronic factors responsible for in situ structural evolution to electroactive species during electrochemical reactions is still in its infancy. Herein, a series of TMTs, MIIWVIO4 (M = Mn/Fe/Co/Ni), have been prepared and employed as electrocatalysts to study the oxygen evolution reaction (OER) under alkaline conditions and to scrutinize the role of transition metals in controlling the energetics of the formation of electroactive species. Since the [WO6]oh unit is common in the TMTs considered, the variation of the central atom of the corresponding [MO6]oh unit plays an intriguing role in controlling the electronic structure and stability of the lattice under anodic potential. Under the OER conditions, a potential-dependent structural transformation of MWO4 is noticed, where MnWO4 appears to be the most labile, whereas NiWO4 is stable up to a high anodic potential of ∼1.68 V (vs RHE). Potential-dependent hydrolytic [WO4]2- dissolution to form MOx active species, traced by in situ Raman and various spectro-/microscopic analyses, can directly be related to the electronic factors of the lattice, viz., crystal field splitting energy (CFSE) of MII in [MO6]oh, formation enthalpy (ΔHf), decomposition enthalpy (ΔHd), and Madelung factor associated with the MWO4 ionic lattice. Additionally, the magnitude of the Löwdin and Bader charges on M of the M-μ2-O-W bond is directly related to the degree of ionicity or covalency in the MWO4 lattice, which indirectly influences the electronic structure and activity. The experimental results substantiated by the computational study explain the electrochemical activity of the TMTs with the help of various structural and electronic factors and bonding interactions in the lattice, which has never been realized. Therefore, the study presented here can be taken as a general guideline to correlate the reactivity to the structure of the inorganic materials.

Electrochemical Behavior of the Oxidative Dissolution of Gold Catalyzed by Lead Ion in Thiourea Solution

ABSTRACT Thiourea is a low-toxicity gold lixiviant that has promise to substitute highly toxic cyanide for gold extraction. The electrochemical behavior of lead ion in the dissolution of gold in thiourea solution was investigated by electrochemical and analytical technique. Electrochemical results suggest that the addition of lead ion (10 mg/L and 20 mg/L) to thiourea solution increased the open circuit potential from 0.31 V to 0.32 V and 0.34 V, respectively, due to the significant increase of cathodic current density. The presence of lead ion could significantly improve the oxidative dissolution of gold and thus resulted in higher gold dissolution in thiourea solution, particularly at higher anodic potentials. The scanning electron microscope (SEM) equipped with energy dispersive spectroscope (EDS) and X-ray photoelectrode spectroscopy (XPS) analyses indicate the improvement of gold dissolution is attributed to the formation of gold-lead (AuPb2) layer on gold surface, which acts as a cathode to promote galvanic corrosion of gold. The possible mechanism is proposed that gold dissolution in thiourea solution with lead ion follows a two-step process: (1) the formation of AuPb2 layer on gold surface and (2) the dissolution of AuPb2 layer under the applied anodic potential.

Enhanced Urea Oxidation Electrocatalytic Activity by Synergistic Cobalt and Nickel Mixed Oxides.

Exploring reactive and selective Ni-based electrocatalysts for the urea oxidation reaction (UOR) is crucial for developing urea-related energy conversion technologies. Herein, synergistic interactions in Ni/Co mixed oxides/hydroxides enhanced the UOR with low onset potential, fast reaction kinetics, and good selectivity against the oxygen evolution reaction (OER). Our electrochemical measurements and theoretical calculations signified the collaborative interaction of Ni/Co mixed oxide/hydroxide heterostructures to enhance UOR activity. Our results showed that Ni3+ species, formed at high anodic potential, produced a high anodic current primarily from unwanted OER. Instead, the Ni/Co heterostructures with dominant Ni2+ and Co3+ species remained stable at low anodic potential and exhibited anodic current exclusively attributed to UOR. This work highlights the importance of tuning valence charges for designing high-performance and selective UOR electrocatalysts to benefit the environmental remediation of urea runoff and enable urea electrolysis for hydrogen production by replacing conventional OER with UOR at the anode.

The Interplay of Anodic Passivation and Oxygen Evolution of Medium Entropy Alloys in Artificial Seawater

Medium entropy alloys (MEA) have gained increased interest in both academic and industrial sectors due to their favorable mechanical and anti-corrosion properties, rendering them ideal candidates for engineering and potentially catalytic applications. Although previous studies have shown high current densities at high anodic potentials for MEAs, a lack of understanding on the underlying transpassive dissolution and local corrosion behavior remains.This project aimed to investigate and compare the passivation behavior of MEAs CrCoNi and FeCrNi (equimolar) under high anodic potentials, focusing on the mechanisms of transpassive dissolution and the oxygen evolution reaction in artificial seawater. The study utilized various techniques such as scanning electrochemical microscopy (SECM) to instantaneously detect evolving metal species and oxygen, and inductively coupled plasma mass spectrocmetry (ICP-MS) to quantify the dissolved metal species. For these investigations, the alloys were subjected to precisely controlled corrosion loads employing potentiodynamic, potentiostatic, and chronoamperometric methods during the SECM experiments and subsequent ICP-MS analysis.Macroscopic corrosion and passive film properties were studied via potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and X-Ray Photoelectron Spectroscopy (XPS). Finally, in-situ atomic force microscopy (AFM) and scanning Kelvin probe force microscopy (SKPFM) were used to analyze the corrosion morphology and surface potentials before, during, and after passivity breakdown. Overall, this study aimed to provide a comprehensive understanding of the interplay between passivation, anodic dissolution and oxygen evolution of the MEAs in artificial seawater.

In situ repairing solid electrolyte interphase of faded graphite electrodes using a temperature–voltage coupling method

The thickening of the solid electrolyte interphase (SEI) increases battery polarization and severely impedes the long cycle life of graphite electrodes. We developed an in situ temperature–voltage coupling method that factors high temperature and high anode potential to decrease the SEI thickness of graphite anodes. A thin and inorganics-rich SEI film is formed upon graphite anode by the method, which is electrochemically and thermally stable. Electrochemical studies revealed that the impedance of the SEI film decreased when the Li/graphite–steel half cells were charged. X-ray photoelectron spectroscopy analysis verified that the proposed method promoted organic-component decomposition within the SEI film. Transmission electron microscope analysis of the morphology revealed SEI thickness reduction. The SEI thickness is plummeted using the proposed method. Thus, this research introduces an innovative method to reconstruct a compact and thin SEI film on the faded graphite anode surface.

Oxidation mechanism of pyrite in a thiosulfate solution: electrochemical impedance (EIS) and in situ Raman spectroscopy

Ammoniacal thiosulfate has been used lately as an alternative lixiviant for leaching gold from sulfides ores which are not amenable for cyanidation. However, the oxidation of the sulfide minerals generates products that inhibit the dissolution of gold and can promote the degradation of the leaching solution. The complexity of the ammoniacal thiosulfate leaching system has prevented the unification and clarification of the mechanisms of oxidation of sulfide ores used for gold extraction.In this study, a method combining polarization curves, Electrochemical impedance spectroscopy (EIS), and in situ Raman spectroscopy was implemented to investigate the oxidation process of high-purity pyrite. Pyrite samples were dispersed in carbon paste electrode (CPE-Py). The polarization curves of CPE-Py exhibited an increase in current values for overpotentials greater than 0.1 V, indicating the initiation of mineral oxidation processes. Subsequently, a maximum current was observed initially, followed by subsequent decrease, indicating the occurrence of passivation processes on the electrode surface. Hydrodynamic polarization curves demonstrated that the overpotential at which the passivation process occurs is independent of mass transport, suggesting that the passivation products were formed through solid-state transformation.Impedance spectra revealed that at overpotentials below 0.1 V, a partially resolved capacitive semicircle was observed, which was associated with the resistance encountered when charge was transferred between the solution and the surface layer interface. This resistance decreased as the polarization overpotential increased, implying a decrease in charge transfer kinetics. At higher overpotentials (0.3 V–0.4 V), a second capacitive semicircle appeared, linked to the oxidation of one or several species present in the mineral.In situ Raman spectroscopy was utilized to identify the oxidation species of pyrite in ammonia-thiosulfate ((NH4)2S2O3) leaching solution at a pH = 10.2. The composition of the species varied depending on the applied anodic potential. At low anodic potentials (0.1 V), Fe(OH)2 and thiosulfate (S2O32−) were formed, while at high anodic potentials (0.4 V), iron products such as Fe3O4 and γ-FeOOH, as well as sulfide species including thiosulfate, tetrathionates and sulfates (S2O32−, S4O6−2 and SO42−) were formed.

Anodik Polarizasyon ve Kayma Aşınmasının Gemi İnşa Alüminyum Alaşımı 5083'ün Çukurcuk Korozyonu Davranışına Etkisi

This study aimed to characterize the pitting corrosion and simultaneous wear-corrosion (tribocorrosion) mechanisms of shipbuilding aluminum alloy 5083 under sliding wear and different anodic polarization conditions in simulated seawater. A tribocorrosion experimental setup was provided for the study under a 3 N load and different anodic potentials in a 3.5% NaCl solution. In the study, many grooves, parallel scratches and transverse cracks were determined on the wear track surface due to the low hardness of the test material. Chloride ions played a decisive role in the corrosion and tribocorrosion behavior of AA 5083. The dissolution of AA5083 increased from open circuit potential to higher anodic potentials. A half-cube mechanism, similar to the pitting corrosion of pure aluminum, and an intergranular pitting corrosion mechanism were observed under high anodic potentials.

Enhanced sulfate recovery from high salinity reject brine through simultaneous chemical precipitation and electrocoagulation

A modified electrocoagulation method is proposed for the recovery of sulfate from high salinity reject brine. This method is based on recovering sulfate using highly/moderately alkaline solids, namely, calcium oxide (CaO), barium hydroxide (Ba(OH)2), hydroxyethyl cellulose (HEC), and ladle furnace slag (LFS), which are added to high salinity water at specific concentrations, in combination with electrocoagulation at specific current densities. This method does not require a prior chemical precipitation, minimizes the required energy input, and the collected solid products can be further purified using conventional methods of separating sulfate from solid mixtures. The system comprises an electrocoagulation unit with alkaline solids at certain operating and mixing conditions. Rectangular aluminium plates were used as electrodes for the electrocoagulation reactor. A current density of 4.5–22.5 mA/cm2 is applied using a power source. The method involved generating electrons at the anode under moderate to high pH conditions and specific anodic potential. The cathode facilitated the production of hydrogen gas and hydroxyl ions, which effectively improved the dissociation of dissolved sulfate components. Combining the chemical precipitation and electrocoagulation in the presence of CaO in one process, a high sulfate removal was achieved from an initial concentration of 6051 mg/L to 196 mg/L in real reject brine after 4 h of treatment. Furthermore, the sulfate removal efficiency reached up to 88% using HEC, 87% using LFS, and 98% using barium hydroxide. In addition, the barium ions in the treated brine reduced up to 64%. The process led to the precipitation of solid compounds specifically, calcium sulfate (CaSO4) using CaO and LFS, and barium sulfate (BaSO4) using Ba(OH)2 and acid fuchsin (C20H12N3Na2O9S3) using HEC. The modified method resulted in an energy reduction of 40% from 14.1 kW h/kg SO42− to 8.5 kW h/kg SO42− compared with the conventional hybrid process.

The Oxygen Evolution Reaction Drives Passivity Breakdown for Ni-Cr-Mo Alloys.

Corrosion is the main factor limiting the lifetime of metallic materials, and a fundamental understanding of the governing mechanism and surface processes is difficult to achieve since the thin oxide films at the metal-liquid interface governing passivity are notoriously challenging to study. Here, a combination of synchrotron-based techniques and electrochemical methods are used to investigate the passive film breakdown of a Ni-Cr-Mo alloy used in many industrial applications. This alloy is found to be active toward oxygen evolution reaction (OER), and the OER onset coincides with the loss of passivity and severe metal dissolution. The OER mechanism involves the oxidation of Mo4+ sites in the oxide film to Mo6+ that can be dissolved, which results in passivity breakdown. This is fundamentally different from typical transpassive breakdown of Cr-containing alloys where Cr6+ is postulated to be dissolved at high anodic potentials, which was not observed here. At high current densities, OER also leads to acidification of the solution near the surface, further triggering metal dissolution. OER plays an important role in the mechanism of passivity breakdown of Ni-Cr-Mo alloys due to their catalytic activity, and this effect needs to be considered when studying the corrosion of catalytically active alloys. This article is protected by copyright. All rights reserved.

A Comparative Study on the Activity and Stability of Iridium-Based Co-Catalysts for Cell Reversal Tolerant PEMFC Anodes

In fuel cell applications with long lifetime requirements, the management of stressing operating conditions—such as hydrogen starvation events—plays a pivotal role. Among other remedies, the incorporation of an OER-enhancing co-catalyst, is widely employed to improve the intrinsic stability of Pt/C-based anode catalyst layers in PEM fuel cells. The present study investigates several supported and unsupported Ir-based co-catalysts comprising different oxidation states of iridium: from metallic to oxidic character, both anhydrous rutile-type IrO2 and hydrated amorphous form. Utilizing a single-cell setup, cell reversal experiments were conducted initially after break-in of the MEA and after seven days of continuous operation under reductive H2 atmosphere at application-relevant conditions. The initial cell reversal tolerance was found to increase in the order metallic Ir < crystalline Ir oxide < amorphous Ir oxyhydroxide. By contrast, after continuous operation under H2 the order changes drastically to amorphous Ir oxyhydroxide ∼ metallic Ir < crystalline Ir oxide. This led us to conclude that the amorphous Ir oxyhydroxide is likely reduced to metallic Ir during continuous H2 operation, while IrO2 provides a reasonable trade-off between initial OER activity, high structural and chemical stability at high anode potentials during H2 starvation and low reducibility under prolonged H2 operation.

A unique sandwich-structured Ru-TiO/TiO2@NC as an efficient bi-functional catalyst for hydrogen oxidation and hydrogen evolution reactions

Developing active and stable non-Pt electrocatalysts for hydrogen oxidation (HOR) and evolution reactions (HER) are critical for anion exchange membrane fuel cells and water electrolyzers. Herein, we report a highly active and robust electrocatalyst Ru-TiO/TiO2@NC, in which Ru nanoclusters are sandwiched between TiO/TiO2 nanosheets and nitrogen-doped carbon layers. Taking advantage of both the optimized Ru-TiO/TiO2 interaction and the conductive carbon coating layers, the Ru-TiO/TiO2@NC exhibits both exceptional HOR/HER activity and superior stability, outperforming Pt/C in the alkaline solution. The HOR mass activity reaches up to 107.2 A gRu-1 at an overpotential of 50 mV, and the specific exchange current density is 0.271 mA cm−2. The HER overpotential at 10 mA cm−2 is only 39 mV, 34 mV lower than required by Pt/C. More importantly, the Ru-based catalyst exhibits excellent anti-oxidation ability by virtue of the unique sandwich structure. Density functional theory calculations discover that the d-band center of Ru in Ru-TiO/TiO2 is downshifted by 0.29 eV compared to Ru-TiO2, decoupling and optimizing the Had/OHad adsorption on Ru, i.e., Had is promoted, while OHad is inhibited and transferred to TiO/TiO2. As a result, (i) the energy required by the potential determining step of HOR/HER is lowered, and (ii) the anti-oxidation ability of the Ru-TiO/TiO2 is enhanced. This work not only addresses the issue of Ru passivation at high anode potentials but also provides an innovative and versatile approach to designing advanced electrocatalysts.

Electrodeposited Ni-P electrodes: An effect of amorphous structure on the electrochemical behavior and electrocatalytic activity in the hydrogen oxidation reaction in alkaline media

Glassy carbon supported Ni/GC and amorphous Ni-P/GC electrodes were prepared by potentiostatic electrodeposition. The catalysts have been characterized by X-ray powder diffraction, transmission and scanning electron microscopy, and cyclic voltammetry. Particular attention has been paid to the influence of electrochemical oxidation on the electrochemical behavior of Ni-P/GC and Ni/GC electrodes in alkaline media as well as the activity of these electrodes in the hydrogen oxidation reaction (HOR). It was found that the oxidation treatment changes the properties of Ni/GC electrode due to the formation of active Ni/NiOx surface sites, while insignificantly affecting the performance of Ni-P/GC sample. The unordinary behavior of electrodeposited Ni-P/GC samples is tentatively attributed to their amorphous structure and the formation of nickel phosphate under high anodic potentials, which prevents the formation of irreversible Ni oxides.