Half-reaction Research Articles

Insights over the in-situ grown copper sulfide/NiFe-LDH composites for alkaline and urea water electrolysis

Harnessing hydrogen fuel through electrocatalytic water splitting offers an eco-friendly alternative to the traditional fossil fuels. The oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are the two half-cell reactions, that make up the electrocatalytic water splitting. Replacing the sluggish OER in the electrocatalytic water splitting with less energy demanding urea oxidation reaction (UOR) might benefit overall water splitting with reduced cell voltages. On the other hand, developing electrodes based on non-precious metals is essential for cost-effective and efficient water splitting. Herein, composites comprising non-precious nickel iron layered double hydroxide (NiFe-LDH) and copper (II) sulfide (CuS) are grown over the nickel foam and subjected to electrochemical measurements for alkaline water electrolysis (AWE) and urea water electrolysis (UWE). Structural and morphological investigations reveal that the 10 wt% CuS composited NiFe-LDH (NFCS10) is supposed to have effective catalytic features for water electrolysis. The electrochemical investigations in the three-electrode system with silver/silver chloride (Ag/AgCl, reference electrode) and platinum (Pt, counter electrode) revealed that the NFCS10 requires only a minimal overpotential (Ƞ50) of 235 mV for UOR and 400 mV for OER respectively. For bifunctional performance, NFCS10 requires an overall cell potential (OCP) of 1.65 V and 1.50 V to reach 10 mA/cm2 current density in AWE and UWE, respectively. X-ray photoelectron spectroscopy identifies the enrichment of oxygen vacancies in NiFe-LDH:CuS heterostructure, which could influence the charge transport and stability of the proposed electrode. This study emphasizes the interfacial interactions between the LDH and metallic sulfide, as well as their impact on the electrocatalytic activity in alkaline and urea water splitting.

In Situ Anodic Transition and Cathodic Contamination Affect the Overall Voltage of Alkaline Water Electrolysis

NiFe (oxy)hydroxide has been widely used as a benchmark anodic catalyst for oxygen evolution reactions (OERs) in alkaline water electrolysis devices; however, the energy saving actually takes contributions from both the anodic OER and cathodic hydrogen evolution reaction (HER). In this work, we observe the catalytic promotion upon the in situ-derived NiFe (oxy)hydroxide from the NiFe alloy monolithic electrode and also point out that the coupled nickel cathode is contaminated, leading to the loss of HER activity and a reduction in overall efficiency. It is found that Ni2+ and Fe3+ cations are inevitably detached from the anode into the electrolyte and electrodeposited on the nickel cathode after the three-month industrial simulation. This research presents the significant enhancement of the oxygen evolution catalysis using an in situ aging process and emphasizes that the catalytic application should not only be isolated on the half reaction, but a reasonable coupled electrode match to get rid of the contamination from the electrolyte is also of great significance to sufficiently present the intrinsic catalytic yielding for the real application.

Research Progress of High-entropy Oxides for Electrocatalytic Oxygen Evolution Reaction.

High-entropy oxides (HEOs), similar to high-entropy materials (HEMs), have "four-core effects", i. e., high-entropy effect, delayed diffusion effect, lattice distortion effect and cocktail effect, which have attracted more and more attention in the scientific field of renewable energy technology due to their unique structural characteristics, variable chemical composition and corresponding functional properties. HEOs have become potential candidates for electrocatalytic oxygen evolution reaction (OER), which is a key half reaction for electrolytic CO2, nitrogen reduction, and water electrolysis. However, the precise synthesis of HEOs with a wide range of components and structures is challenging, not to mention their active and stable operation for OER. In this paper, we review the recent advancements in the electrocatalytic oxygen evolution facilitated by HEOs in water electrolysis. We analyze these developments from the perspectives of activity and stability in acid and alkaline conditions, respectively. Furthermore, we summarize the design from the aspect of element composition, structure, morphology, and catalyst-support interactions, along with related reaction mechanism of HEOs. Additionally, we discuss the current challenges faced by HEOs in the field of OER and suggest potential directions for the future development of HEOs beyond water electrolysis application.

The Effect of Electrochemical Ageing of Glassy Carbon Electrodes on VII-VIII and VIV-VV Kinetics

Electrode activity towards the negative and positive half-cell reactions of a vanadium flow battery were investigated. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to monitor electrode activity of glassy carbon electrodes towards VII-VIII and VIV-VV redox reactions during electrochemical ageing through repeated anodic and cathodic treatments. Electrode activity is found to increase with number of treatment steps, showing little difference initially between anodised and cathodised electrodes. However, after several treatments, a potential-differentiated behaviour emerges, with distinct enhanced and inhibited states. For VII-VIII, anodised electrodes showed enhanced activity, while cathodised electrodes were inhibited. Conversely, for VIV-VV, cathodised electrodes had enhanced activity. In almost all cases, the activity is greater than that of an untreated electrode. Eventually, electrode activities stabilise in a steady-state region where activity depends on the final treatment potential rather than the number of steps. In this region, activity can be toggled reproducibly between enhanced and inhibited states. Therefore, it can be concluded that functional groups, rather than surface roughening or defect formation, are responsible for this toggling capability. Furthermore, for VIV-VV, steady-state activity levels and the number of treatment steps required to reach this region are found to be dependent on the upper and lower treatment potentials.

Anodic Commodity Polymer Recycling: The Merger of Iron-Electrocatalysis with Scalable Hydrogen Evolution Reaction.

Plastics are omnipresent in our everyday life, and accumulation of post-consumer plastic waste in our environment represents a major societal challenge. Hence, methods for plastic waste recycling are in high demand for a future circular economy. Specifically, the degradation of post-consumer polymers towards value-added small molecules constitutes a sustainable strategy for a carbon circular economy. Despite of recent advances, chemical polymer degradation continues to be largely limited to chemical redox agents or low energy efficiency in photochemical processes. We herein report a powerful iron-catalyzed degradation of high molecular weight polystyrenes through electrochemistry to efficiently deliver monomeric benzoyl products. The robustness of the ferraelectrocatalysis was mirrored by the degradation of various real-life post-consumer plastics, also on gram scale. The cathodic half reaction was largely represented by the hydrogen evolution reaction (HER). The scalable electro-polymer degradation could be solely fueled by solar energy through a commercially available solar panel, indicating an outstanding potential for a decentralized green hydrogen economy.

Anodisches Recycling von gängigen Polymeren: Die Kombination von Eisen‐Elektrokatalyse und skalierbarer Wasserstoffentwicklungsreaktion

AbstractKunststoffe sind in unserem Alltag allgegenwärtig, und die Akkumulation von Kunststoffabfällen in unserer Umwelt stellt ein großes gesellschaftliches Problem dar. Daher sind Methoden für das Recycling von Kunststoffabfällen im Hinblick auf eine künftige Kreislaufwirtschaft von hohem Interesse. Insbesondere der Abbau von Polymeren nach Nutzung durch Verbraucher hin zu wertschöpfenden kleinen Molekülen stellt eine nachhaltige Strategie für eine Kohlenstoff‐Kreislaufwirtschaft dar. Trotz jüngster Fortschritte ist der chemische Polymerabbau nach wie vor weitgehend auf chemische Redox‐Reagenzien beschränkt oder durch eine geringe Energieeffizienz photochemischer Prozesse limitiert. In dieser Arbeit berichten wir über einen leistungsstarken eisenkatalysierten Abbau von Polystyrolen mit hohem Molekulargewicht durch Elektrochemie, um effizient monomere Benzoylprodukte zu liefern. Die Robustheit der Ferraelektrokatalyse wurde durch den Abbau von verschiedenen realen Nach‐Gebrauchs‐Kunststoffen, ebenfalls im Gramm‐Maßstab, bestätigt. Die kathodische Halbreaktion wurde weitgehend durch die Wasserstoffentwicklungsreaktion (HER) dargestellt. Der skalierbare elektrolytische Polymerabbau konnte ausschließlich mit Solarenergie über ein handelsübliches Solarpanel betrieben werden, was auf ein herausragendes Potenzial für eine dezentralisierte, grüne Wasserstoffwirtschaft hinweist.

Vanadium-Doped Ni3S2: Morphological Evolution for Enhanced Industrial-Scale Water and Urea Electrolysis.

The development of an earth abundant, cost-effective, facile and multifunctional 3D-porous catalytic network for green hydrogen production is a tremendous challenge. Herein, we report the V-Ni3S2 self-supported catalytic network with optimized morphology grown directly on nickel foam (NF) by the one-step hydrothermal technique for water and urea electrolysis at industrial scale hydrogen generation. The morphology of Ni3S2 was modulated by doping of different concentrations of vanadium from granules to cross-linked wires to hierarchal nanosheets arrays, which is beneficial in electrochemical charge and mass transport, and generates more exposed active sites. The V-Ni3S2 catalyst requires the overpotential of 147 mV for hydrogen evolution reaction (HER). The OER and UOR half-cell reaction on V-Ni3S2 catalyst requires potential 1.57 V and 1.39 V (vs RHE), respectively to generate current 100 mA/cm2. The water electrolysis cell developed by V-Ni3S2 as both anode and cathode generates 100 mA/cm2 at cell voltage of 1.88 V in laboratory condition (1 M KOH, 25 °C) and 1.61 V at industrial condition (5 M KOH, 80 °C) and also shows considerable stability for 82 hr at current 300 mA/cm2. The urea electrolysis cell with 1 M KOH and 0.33 M urea generates 100 mA/cm2 at a cell voltage of 1.73 V, which is 150 mV less than that required for water electrolysis and demonstrate stability for 85 hr at a current of 100 mA/cm2. The results provide an innovative plan for the considerate synthesis and design of bifunctional catalysts for energy storage and water splitting.

Two conserved arginine residues facilitate C-S bond cleavage and persulfide transfer in Suf family cysteine desulfurases.

Under conditions of oxidative stress or iron starvation, iron-sulfur cluster biogenesis in E. coli is initiated by the cysteine desulfurase, SufS, via the SUF pathway. SufS is a type II cysteine desulfurase that catalyzes the PLP-dependent breakage of an L-cysteine C-S bond to generate L-alanine and a covalent active site persulfide as products. The persulfide is transferred from SufS to SufE and then to the SufBC2D complex, which utilizes it in iron-sulfur cluster biogenesis. Several lines of evidence suggest two conserved arginine residues that line the solvent side of the SufS active site could be important for function. To investigate the mechanistic roles of R56 and R359, the residues were substituted using site-directed mutagenesis to obtain R56A/K and R359A/K SufS variants. Steady state kinetics indicated R56 and R359 have moderate defects in the desulfurase half reaction but major defects in the transpersulfurase step. Fluorescence polarization binding assays showed that the loss of activity was not due to a defect in forming the SufS/SufE complex. Structural characterization of R56A SufS shows loss of electron density for the α3-α4 loop at the R56/G57 positions, consistent with a requirement of R56 for proper loop conformation. The structure of R359A SufS exhibits a conformational change in the α3-α4 loop allowing R56 to enter the active site and mimics the residue's position in the PLP-cysteine aldimine structure. Taken together, the kinetic, binding, and structural data support a mechanism where R359 plays a role in linking SufS catalysis with modulation of the α3-α4 loop to promote a close-approach interaction of SufS and SufE conducive to persulfide transfer.

An electrocatalytic iodine oxidations-based configuration for hydrogen and I2/I3− co-productions driven by the Zn-air/iodine battery

Electrochemical water splitting and energy storage are key for a sustainable energy future, despite the challenges related to undesirable overpotentials and high voltage requirements. Herein, we introduce a synergistic approach between a low overpotential hydrogen evolution reaction (HER) and a low voltage zinc-air/iodine battery (ZAIB) by coupling with iodide oxidation half reactions. By developing a Pt/Co3O4 electrocatalyst in two steps and with under 2% Pt loading, we achieve an unprecedented low full cell potential for hydrogen generation at 0.574 V, exhibiting an ultra-high reduction of energy consumption of 64.7%. The Pt/Co3O4 electrode also enables ZAIB to record a power density of 154 mW cm−2 at an ultra-low charging potential of 1.68 V. Mechanistic studies and DFT calculations of the novel electrode confirm an electron rich Pt-Co interface and favorable Pt-I interactions, facilitating both HER and IOR reactions. Our design provides critical technology for potential large-scale renewable energy projects.

Synthesis of a new quaternary ammonium salt for efficient inhibition of mild steel corrosion in 15 % HCl: Experimental and theoretical studies

The corrosion phenomenon and its economic impacts can hardly be ignored in any application. This study synthesized a quaternary ammonium salt (3) containing hydrophobic dodecyl and electron-rich diallylbenzyl amine moieties to be used in 15 % HCl as a corrosion inhibitor of mild steel. Several techniques, such as 1H and 13C NMR, IR, TGA, and elemental analysis, have been used to characterize inhibitor 3. Popular corrosion measurement techniques, namely weight loss, potentiodynamic polarization techniques, and electrochemical impedance spectroscopy, have been used to determine the efficiency of inhibitor 3. At 303 K and a moderately low concentration of 50 ppm, the quaternary ammonium salt-based inhibitor demonstrated a maximum efficiency of ≈95.0 %. At elevated temperatures of 313, 323, and 333 K, the inhibition efficacy values were recorded as 91.3, 82.8, and 75.0 %, respectively. Adsorption isotherm study revealed that the adsorption of inhibitor 3 followed Langmuir adsorption isotherm. The value of ΔGads° was found to be – 40.19 kJ mol−1, indicating that inhibitor 3 became adsorbed via a mixed physi-chemisorption mechanism. A very high adsorption constant (Kads) of 1.53 × 105 L mol−1 suggested strong adsorption of inhibitor 3. The difference in activation energy (Ea) value of 42.4 kJ mol−1 between the control and the inhibited solution indicated an efficient adsorption of inhibitor 3. The ability of inhibitor 3 to retard both anodic and cathodic half-cell reactions was proved via open circuit potential and Tafel curves studies. Detailed discussions on the change in corrosion current densities (icorr), polarization (Rp) and charge transfer (Rct) resistances have been offered to discuss the inhibition efficiency. Water contact angle measurement showed a drastic increase in mild steel surface hydrophobicity following inhibitor 3 adsorption. SEM-EDX and XPS studies confirmed the definitive presence of inhibitor 3 on the mild steel surface. Density functional theory (DFT) studies revealed the frontier molecular orbitals with which the metal surface interacts. A detailed corrosion inhibition mechanism has been offered in the context of adsorption isotherm and DFT studies.

Disentangling heterogeneous thermocatalytic formic acid dehydrogenation from an electrochemical perspective

Heterogeneous thermocatalysis of formic acid dehydrogenation by metals in solution is of great importance for chemical storage and production of hydrogen. Insightful understanding of the complicated formic acid dehydrogenation kinetics at the metal-solution interface is challenging and yet essential for the design of efficient heterogeneous formic acid dehydrogenation systems. In this work, formic acid dehydrogenation kinetics is initially studied from a perspective of electrochemistry by decoupling this reaction on Pd catalyst into two short-circuit half reactions, formic acid oxidation reaction and hydrogen evolution reaction and manipulating the electrical double layer impact from the solution side. The pH-dependences of formic acid dehydrogenation kinetics and the associated cation effect are attributed to the induced change of electric double layer structure and potential by means of electrochemical measurements involving kinetic isotope effect, in situ infrared spectroscopy as well as grand canonical quantum mechanics calculations. This work showcases how kinetic puzzles on some important heterogeneous catalytic reactions can be tackled by electrochemical theories and methodologies.

Catalyzed syntheses of novel series of spiro thiazolidinone derivatives with nano Fe2O3: spectroscopic, X-ray, Hirshfeld surface, DFT, biological and docking evaluations

Twelve spiro thiazolidinone compounds (A–L) were synthesized via either conventional thermal or ultrasonication techniques using Fe2O3 nanoparticles. The modification of the traditional procedure by using Fe2O3 nanoparticles led to enhancement of the yield of the desired candidates to 78–93% in approximately half reaction time compared with 58–79% without catalyst. The products were fully characterized using different analytical and spectroscopic techniques. The structure of the two derivatives 4-phenyl-1-thia-4-azaspirodecan-3-one (A) and 4-(p-tolyl)-1-thia-4-azaspirodecan-3-one (B) were also determined using single crystal X-ray diffraction and Hirshfeld surface analysis. The two compounds (A and B) were crystallized in the orthorhombic system with Pbca and P212121 space groups, respectively. In addition, the crystal packing of compounds revealed the formation of supramolecular array with a net of intermolecular hydrogen bonding interactions. The energy optimized geometries of some selected derivatives were performed by density functional theory (DFT/B3LYP). The reactivity descriptors were also calculated and correlated with their biological properties. All the reported compounds were screened for antimicrobial inhibitions. The two derivatives, F and J, exhibited the highest levels of bacterial inhibition with an inhibition zone of 10–17 mm. Also, the two derivatives, F and J, displayed the most potent fungal inhibition with an inhibition zone of 15–23 mm. Molecular docking investigations of some selected derivatives were performed using a B-DNA (PDB: 1BNA) as a macromolecular target. Structure and activity relationship of the reported compounds were correlated with the data of antimicrobial activities and the computed reactivity parameters.

Oxygen-Deficient Thermal Treatment Boosts Performance of Co-Ni-Fe Oxide Electrocatalyst in Oxygen Evolution Reaction

The production of green hydrogen through water electrolysis using electricity generated from renewable sources is one of the most promising strategies toward achieving a carbon-neutral economy.[1-3] Water electrolysis is an effective and well-established water splitting process consisting of two half-cell reactions, the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) at cathode and anode, respectively. Although hydrogen as the value-added product is generated at the cathode, the anodic reaction plays an important role in determining the reaction kinetics of the entire water splitting process due to the multiple-electron transfer.[4] Therefore, developing low-cost and highly active OER electrocatalysts is one of the keys to further improve overall efficiency of water electrolysis. Among various water electrolysis technologies, alkaline water electrolysis (AWE) has been commercialized for many decades and standing for medium-scale hydrogen production and using non-noble metals as electrocatalysts.[5]Co-, Ni-, and Fe- oxides or (oxy)hydroxides are reported as auspicious OER electrocatalysts for AWE, as well as abundance on earth.[6] In addition, oxygen vacancies in metallic oxides are reported recently as an effective approach to enhance catalyst activity for OER.[7] Herein, we present trimetallic oxides (CoNiFe oxides) annealed in different atmospheres which are oxygen-rich (A; air), an oxygen-poor (M; 1 vol% air in argon), and oxygen-free (H; 5 vol% H2 in argon), respectively, The CoNiFe (2:2:1)/M with a molar ratio of Co : Ni : Fe = 2 : 2 : 1 treated under an oxygen-poor atmosphere (M) exhibits the best performance in 1 M KOH, with an overpotential of 291 mV at 10 mA cm-2 geo, a mass activity at 1.56 V versus the reversible hydrogen electrode (RHE) of ~345 A g-1 catalyst, and a small Tafel slope of 32.0 mV dec-1. Moreover, CoNiFe (2:2:1)/M shows excellent stability in the OER process for at least 50 hours at 100 mA cm-2 geo at lab scale and ~75 h at 400 mA cm-2 in an alkaline electrolyzer. This work presents a simple and effective method to design OER catalysts based on trimetallic oxides with oxygen deficiencies for alkaline water electrolysis.

CO2 Reduction in a Bio Mass-Paired Systems for the Production of e-Chemicals

The electrification of chemical manufacturing is an important pathway toward reduced CO2 emissions. Direct electrochemical CO2 reduction can thereby become a key technology. CO2 electrolyzers produce cathodically platform chemicals as CO, format, ethanol or ethylene. The state-of-the-art anode process is the oxygen electro evolution which suffers from high over potentials and moderate valorization. An alternative is the anodic oxidation of biomass to valorized carbonaceous products, such as the oxidation of hydroxymethylfurfural (HMF) to the biopolymer precursor 2.5-furandicarboxylic acid (FDCA).In this work we report the design of electrolyzers flow cells with paired valorization of biomass and CO2. NiNC cathode GDEs are used for CO2 reduction to CO and NiFe-LDH anodes for the HMF oxidation in a zero-gap membrane electrolyzer flow cells. We used a bipolar membrane to separate and optimize either half-cell reactions. Inside the membrane, water is dissociated and the protons will neutralize carbonates on the cathode which is beneficial for a higher CO2 utilization and single pass. So, we can report close to 95% FE and 100% utilization efficiency towards CO.On the other hand, the hydroxide will stabilize the anode pH and enable PGM-free anodes compared to AEM CO2 electrolyzer. State-of-the-art HMF oxidation is a semi-batch setup, in which the HMF containing anolyte is recycled to complete HMF depletion and utilization. This design suffered from severe mass limitations. Therefore, we modified the semi-batch process into a continuous process and made tradeoffs between faradaic efficiency and utilization. As HMF is not stable in alkaline solutions we decided that a high utilization is beneficial because the intermediates are stable and could be recycled. We can report a single pass conversion of around 70 % towards FDCA at 200 mA cm-2 at a total utilization of 90%.Figure caption: Paired continuous HMF/CO2 electrolyzer with performance parameter. Figure 1

Application of Bifunctional Layered Double Hydroxide Electrocatalysts to Water Splitting

Water splitting is an area of research which is of pressing interest in addressing climate change. Water splitting provides oxygen and hydrogen as products, with hydrogen finding use as a potential high-density fuel to replace fossil fuels. Water splitting manifests as two half-cell reactions, namely the anodic oxygen evolution reaction and the cathodic hydrogen evolution reaction. The purpose of this project is to synthesise a bifunctional electrocatalyst to use in the water splitting reaction, replacing the rare and expensive transition metals catalysts currently in use such as platinum and ruthenium. The ideal material would exhibit strong performance for both the oxygen evolution reaction and the hydrogen evolution reaction.In this project, Layered Double Hydroxides (LDHs) have been synthesised for use in water splitting. LDHs are a group of ionic compounds characterised by their layered structure of positively charged sheets and an interlayer region consisting of the corresponding anions. LDHs typically contain a bivalent and a trivalent metal as part of the generic formula [M2+ 1–xM3+ x(OH)2][An–]x/n·zH2O. In this project the bivalent metal in use is typically cobalt and the trivalent metal is typically iron. The synthesis developed is a simple, one pot hydrothermal synthesis which can be seen in Figure 1. In this synthesis, the process begins with the precursor materials dissolved in solution. These solutions are mixed and stirred until homogenous. The resultant solution is then heated to form an impure product. Following washing steps and centrifugation a purified powder product is obtained. A variety of metallic salts have been tested for their use in these LDHs with the optimum LDHs selected for further study. The metallic salts used to provide the metals for the LDHs are typically hydrated transition metal nitrates.The LDHs have been characterised and their structure confirmed by a variety of analytical techniques including X-Ray Diffraction and Scanning Electron Microscopy. Simple qualitative analysis has been performed with FTIR spectroscopy. These LDHs have been immobilised on a variety of porous, high surface area materials, including nickel foam and copper foam, to enhance the properties seen in the screening study. These materials allow synthesis of high surface area, reactive electrocatalysts. To enhance the stability of the LDHs, carbon materials have been integrated with the LDHs. Examination of a variety of carbon materials involved post-synthesis mixing of the carbon material and the LDH product or inclusion of the carbon material in the LDH synthesis to form a composite. A variety of carbon materials have been analysed including graphene oxide, carbon black and carbon nanotubes. Figure 1

Pt/C and PtRu/C Catalysts Prepared by Modified Sulfite Complex Routes for Fuel Cell Applications

In-house 30 wt.% Pt and 50 wt.% Pt1Ru1 catalysts supported on high-surface area carbon (Ketjenblack, abbreviated as KB) were synthesized by the sulfite complex route. Two different procedures involving either a direct mixing of Pt-sulfite and Ru-sulfite complexes or Pt-sulfite preparation and subsequent impregnation of Ru precursor were adopted for the bimetallic species. In both cases, an impregnation of the formed metal oxides onto KB was adopted to increase the electronic conductivity of the samples. Finally, a carbothermal treatment at 600°C in He atmosphere was carried out for the reduction of the metal oxides to metallic PtRu/C compounds. The Pt1Ru1 ratio was calculated and revealed by X-ray fluorescence (XRF) analysis whereas the carbon percentage was calculated by weight loss. 50 mg of sample was treated in air at 550°C for 2 h and, after cooling, the weight corresponded to 25 mg, confirming a carbonaceous matrix percentage of 50 wt.%. In a similar way, the 30 wt.% Pt/C was determined. X-ray diffraction (XRD) revealed that the samples showed face centered cubic (fcc) structure for Pt nanoparticles. It appears that two distinct crystallographic phases of Pt and Ru nanoparticles were encountered after the synthesis conducted by Ru impregnation. In contrast, only a single fcc phase is visible when the Pt and Ru sulfite precursors were mixed, confirming the formation of an alloy. Furthermore, Scanning Transmission Electron Microscopy-Energy dispersive X-ray spectroscopy (S/TEM-EDX) and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the differences in morphology and surface characteristics of the catalysts.For the electrochemical measurements, rotating disc electrode (RDE) technique under acid and alkaline conditions was employed to investigate the half cell reactions. The catalysts were also deposited at the anode and cathode of fuel cells to evaluate the activity, performance, and short-term durability. Acknowledgement “This research was funded by the European Union – EIT Raw Materials in the framework of the following project: LYDIA- Recycling Critical Metals from Fuel Cells (G.A. 22019)”

Superior Activity of Carbon Felt Coated with PEDOT and Titanium Oxide Double Layers Towards V(II)/(VIII) Reaction in Redox Flow Batteries

Energy consumption has become a great problem in the last few decades due to the dramatic increment in population and solo dependence on fossil fuels to fulfill energy requirements. The intense consumption of these limited non-renewable resources had harmful effects on humanity, making the adoption of renewable energy resources compulsory. High-efficiency storage systems are necessary for the integration of renewable energy sources into the electrical grid and for the provision of that energy when needed. For this application, all-vanadium redox flow batteries (VRFBs) hold great promise because of their high energy storage capacity, extended operational life, and long-life reusable solutions1. The enhancement of RFBs should be taken from many perspectives such as the enhancement of electrodes, membranes, or even the design of the cell. Enhancing the electrode performance is one of the important challenges that attracted the attention of researchers, with a variety of electrode modifications that have been studied such as using carbon, metals, and metal oxide materials2,3. Over a large number of metal oxides, TiO2 possesses interesting catalytic properties as it has been used in sensors, Li-ion batteries, and electrocatalysis, in addition to its ability to suppress the hydrogen evolution reaction (HER) which was a stumbling block for the negative side of VRFBs4.The goals of this work are to suppress the parasitic reaction of hydrogen evolution and improve the kinetics of the VRFBs' negative half-cell reaction (V(II)/V(III)). To achieve this goal, coating carbon felt (CF) with poly(3,4-ethylenedioxythiophene) (PEDOT) and Titanium Oxide double layers was proposed. The underlayer of PEDOT is expected to enhance the TiOx conductivity, and hence its electrocatalytic activity, but without enhancing the parasitic HER5. The PEDOT layer was formed using chronopotentiometric electropolymerization method, followed by the deposition of a TiOx layer using a solvothermal method. To understand the effect of the PEDOT and TiOx layers on the final electrode activity towards V(II)/V(III) redox reaction, several electrodes (CF\\PEDOT, CF\\G-PEDOT, CF\\TiOx CF\\PEDOT\\TiOx, and CF\\G-PEDOT\\TiOx) were fabricated. The physical and chemical properties of the synthesized electrodes were characterized using XRD, FESEM, EDX, UV-vis DRS, Raman spectroscopy, FTIR, contact angle measurements, and XPS. The performance of the fabricated electrodes towards V(II)/V(III) redox reaction was evaluated in 3-electrode and 2-electrode setups, using cyclic voltammetry, electrochemical impedance spectroscopy, and charging/discharging methods. The addition of an underlayer of PEDOT is found to generally enhance the TiO2 activity as a negative electrode in VRFB. References R. K. Sankaralingam, S. Seshadri, J. Sunarso, A. I. Bhatt, and A. Kapoor, J. Energy Storage, 41, 102857 (2021).Z. Huang, A. Mu, L. Wu, and H. Wang, J. Energy Storage, 45, 103526 (2022).Y. Lv et al., J. Mater. Sci. Technol., 75, 96–109 (2021).J. Vázquez-Galván et al., ChemSusChem, 10, 2089–2098 (2017).M. Heydari Gharahcheshmeh et al., Adv. Mater. Interfaces, 7, 2000855 (2020).

Lanthanum Transition-Metal Sulfide Electrocatalysts for Overall Water Splitting

Hydrogen has been identified as a sustainable energy source for the future with the potential of replacing fossil fuels due to its high gravimetric energy density and zero carbon emissions. Water electrolysis is a promising approach to the clean production of pure hydrogen, however, the benchmark catalysts of the half reactions of water electrolysis are noble-metal based, which limit the application of this technique.1 As well, the high energy barrier and sluggish kinetics of the oxygen evolution reaction limit the efficiency of the system. Therefore, it is crucial to develop robust, stable, and cost-effective materials for water electrolysis to be scalable. Lanthanum transition-metal oxide electrocatalysts have been pursued in the past for water splitting due to the high abundance of lanthanum and transition metals.2 However, these catalysts suffer from low conductivity and inherent instability towards oxygen evolution. Binary sulfides, selenides, and phosphides have also been pursued,3 but the compositional space of these materials is limited. Ternary sulfides offer a wider compositional space that allows fine-tuning for optimal performance. As a result, we have pursued the synthesis and application of the relatively unexplored ternary chalcogenides, LaMS3 (M = Ni, Co, Fe, Mn) towards water electrolysis. The efficiency of water electrolysis and stability of the materials have been tested with linear sweep voltammetry, galvanostatic measurements, and electrochemical impedance spectroscopy. We found these materials to be active towards both the hydrogen and oxygen evolution reactions, in acidic and alkaline conditions, respectively, with the catalysts exhibiting an activity trend where LaNiS3 > LaCoS3 > LaFeS3 > LaMnS3. For HER, LaNiS3 exhibits an overpotential of 340 mV at 10 mAcm-2 with a Tafel slope of 79 mV/decade. For OER, an overpotential of 373 mV at 10 mAcm-2 and a low Tafel slope of 48 mV/decade are observed. In addition, LaNiS3 proved to be highly stable with minimal change in potential over a period of 18 hours. The high activity and stability of LaNiS3 towards both half reactions of water electrolysis make it a promising candidate for a bifunctional water splitting electrocatalyst.References Wang, S.; Lu, A.; Zhong, C.-J. Hydrogen Production from Water Electrolysis: Role of Catalysts. Nano Convergence 2021, 8 (1), 4.Dias, J. A.; Andrade, M. A. S.; Santos, H. L. S.; Morelli, M. R.; Mascaro, L. H. Lanthanum‐Based Perovskites for Catalytic Oxygen Evolution Reaction. ChemElectroChem 2020, 7 (15), 3173–3192.Anantharaj, S.; Ede, S. R.; Sakthikumar, K.; Karthick, K.; Mishra, S.; Kundu, S. Recent Trends and Perspectives in Electrochemical Water Splitting with an Emphasis on Sulfide, Selenide, and Phosphide Catalysts of Fe, Co, and Ni: A Review. ACS Catal. 2016, 6 (12), 8069–8097.

Mesoporous carbon-doped boron nitrides for cathodic and anodic hydrogen peroxide electrosynthesis

Mesoporous carbon-doped hexagonal boron nitrides (C-doped BN) with high surface area were prepared by annealing organic resin polymer/silica in NaBH4 and NaNH2 inorganic salts, which were found to be efficient metal-free bifunctional electrocatalyst for both 2e− ORR and 2e− WOR. It could efficiently catalyze 2e− ORR to H2O2 in 2 M KHCO3 (1650 mmol g−1 h−1) with Faraday efficiency of 93–98 % in half reaction, while it was very active for 2e− WOR to generate H2O2 in 2 M KHCO3 with 551 mmol g−1 h−1 H2O2 production rate in half reaction. When pairing them in one H-type cell, H2O2 solution could be totally produced over C-doped BN in both anode and cathode cells. The better electron conductivity from sharper band gap caused by carbon doping and higher surface area of 304 m2 g−1 contributed to its efficient electrocatalytic activity. The C-doped BN served an effective bifunctional electrocatalyst for 2e− ORR and 2e− WOR.

Electronic-Structure-Modulated Cu,Co-Coanchored N-Doped Nanocarbon as a Difunctional Electrocatalyst for Hydrogen Evolution and Oxygen Reduction Reactions.

To alleviate the problems of environmental pollution and energy crisis, aggressive development of clean and alternative energy technologies, in particular, water splitting, metal-air batteries, and fuel cells involving two key half reactions comprising hydrogen evolution reaction (HER) and oxygen reduction (ORR), is crucial. In this work, an innovative hybrid comprising heterogeneous Cu/Co bimetallic nanoparticles homogeneously dispersed on a nitrogen-doped carbon layer (Cu/Co/NC) was constructed as a bifunctional electrocatalyst toward HER and ORR via a hydrothermal reaction along with post-solid-phase sintering technique. Thanks to the interfacial coupling and electronic synergism between the Cu and Co bimetallic nanoparticles, the Cu/Co/NC catalyst showed improved catalytic ORR activity with a half-wave potential of 0.865 V and an excellent stability of more than 30 h, even compared to 20 wt% Pt/C. The Cu/Co/NC catalyst also exhibited excellent HER catalytic performance with an overpotential of below 149 mV at 10 mA/cm2 and long-term operation for over 30 h.