Reaction In Acid Medium Research Articles

Porous amorphous high entropy oxide coated dimensionally stable anode for oxygen evolution reaction in acidic media

Oxygen evolution reaction (OER) has been the subject of considerable attention as a pivotal reaction in the hydrogen production and hydrometallurical electrowinning. Precious metal-coated dimensionally stable anodes (DSAs) have wide applications in electrochemical industry, functioning as high-performance and stable electrocatalysts for OER. Given the broad development prospects opened up by the advocacy of green energy, the key to the electrochemical industry lies in improving the catalytic performance and durability of DSA. In this study, a novel porous amorphous Ir-based high-entropy oxides-coated DSA was prepared by thermal decomposition method, and its OER activity and durability in acidic media were investigated. The Ir-based high-entropy oxides coatings exhibit a hierarchical porous morphology at the surface, coupled with an amorphous structure. The coatings display a high proportion of Ir3+, unsaturated bonds and oxygen vacancies/hydroxyl groups, which collectively impart excellent OER activity. The achievement of current densities of 10 and 100 mA cm−2 at potentials of 1.45 and 1.51 V vs. RHE in 0.5 mol L−1 H2SO4 solution represents a significant outcome. The coatings demonstrated remarkable electrochemical durability without decay after 5000 cycles and are able to withstand a cumulative 504-hour durability test under the current density of 1000, 2000, and 3000 mA cm−2.

Insight into the Modification of the Low-Pt Electrocatalysts By the Defective Metal Oxide Additives: The Effect on the Oxygen Reduction Reaction in Acid Media

The global rise in energy consumption combined with severe environmental issues and climate change has promoted the development of green alternative technologies such as low-temperature proton exchange membrane fuel cells (PEMFCs). However, the performance and operational cost of PEMFC largely depend on the application of highly expensive state-of-the-art Pt-based systems, which are so far the most effective catalysts for the oxygen reduction reaction (ORR) at the fuel cell’s cathode. The widespread commercialization of the PEMFC technology has also been complicated by the limited lifetime of catalytic systems due to the instability of carbon supports as well as Pt catalytic centers. Due to these facts, it is of great significance to gain an in-depth insight into the ORR mechanism to optimize the activity of the ORR catalytic centers and their more efficient utilization while minimizing the Pt content without loss of performance and durability, which are essential features to ensure wider use of the low-temperature hydrogen-oxygen fuel cell systems. One of the reasonable strategies for ameliorating stability, and selectivity of carbon-supported low Pt content electrocatalysts for the ORR in acid media is their functionalization by selected nanostructured non-noble metal oxides (MOx)1. The strong mutual interactions between all components in such hybrid material (Pt, C, MOx) are capable of tuning the Pt electronic structure at the electrocatalytic interface, thus promoting centers for the adsorption of oxygen and the cleavage of O=O bonds as well as the durability of the carbon carriers can be improved under highly aggressive acidic conditions. Additionally, the application of metal oxide co-catalysts which are capable of inducing the decomposition of hydrogen peroxide and/or scavenging of free radicals can make a significant contribution to improving the durability and overall efficiency of fuel cells.Due to the unique structure, redox ability, oxygen vacancies, and other features resulting from the 4f electronic configuration of cerium, in the present studies, we synthesis the reduced CeOx nanostructured and investigate the influence of such additive on the stability and selectivity of low-Pt content electrocatalysts in the oxygen reduction reaction (ORR) in acidic media. The stable oxide phases with the tailored redox properties and the presence of oxygen vacancies were obtained by controlling their morphology and composition. Preparation of small ceria nanoparticles by microwave-assisted hydrothermal method and introduction of various dopants (e.g. Pr, Nb, Cu) into these oxide structures improve its reducibility and non-stoichiometry phase content, optimizing important parameters for catalytic activity. The received results revealed that the CeOx/M-CeOx additive is allowed to obtain a lower amount of undesirable H2O2 produced during the ORR and improve the Pt/C stability. It is assumed that the improved durability and the better selectivity towards 4e– reduction of oxygen of the modified catalyst result from the defective cerium oxide properties and strong interactions between all components. Acknowledgments: This research was funded by the National Science Center (Poland) under Sonatina Project (2022/44/C/ST5/00077) and under the auspices of the European Union EIT Raw Materials ALPE 19247 Project (Specific Grant Agreement No. EIT/RAW MATERIALS/SGA2020/1).

Durability and Structural Transformation of Pt Alloy Nanowires and Nanoparticles for the Oxygen Reduction Reaction in Acidic Media

The oxygen reduction reaction (ORR) is catalyzed at the cathode in polymer electrolyte fuel cells (PEFCs). Since the ORR is sluggish and the electrocatalytic activity of the ORR catalyst determines the overall performance of PEFCs, highly active and durable ORR electrocatalysts have been intensively studied. The combination of alloying and nanostructuring of Pt is one of the promising approaches to develop such ORR electrocatalysts. Among the Pt-based shape-controlled electrocatalysts, Pt or Pt–M alloy nanowires (M = Ni and Co) are known to exhibit high ORR activity in the half cell [1,2]. Since nanowires have larger contact areas and therefore potentially higher adhesion to the carbon support than conventional nanoparticles, Pt-based nanowires should have higher durability. However, details of the effect of durability testing (potential cycles) on the structure of nanowires remain unclear.In this work, we report synthesis of PtNi alloy nanowires at different temperatures under different atmospheres, and their structural transformation after potential cycles. PtNi nanowires were prepared at 433 K under Ar and air [3]. The difference in atmosphere affects the presence or absence of PtNi nanoparticles with PtNi nanowires: both PtNi nanowires and nanoparticles are produced under the inert condition of Ar, whereas PtNi nanowires are exclusively produced under the oxidative condition of air. PtNi nanowires with and without PtNi nanoparticles were converted into branched nanostructures after durability tests. PtNi nanowires were also prepared at different temperatures of 433, 493 and 553 K under Ar [4]. The Ni content in the PtNi nanowires increases from <5 at.% up to about 15 at.% with increasing synthesis temperature. The number of PtNi nanoparticles also decreases with increasing synthesis temperature. The PtNi nanowires in the co-presence of PtNi nanoparticles prepared at 493 K gave highly durable beads-on-nanowires with the Pt skin via Ostwald ripening of coexisting PtNi nanoparticles. This structural transformation is coupled with changes in the surface electronic structure, confirmed by in situ X-ray absorption spectroscopy. Understanding such a structural transformation will help us to design and develop highly durable Pt alloy nanostructured electrocatalysts for the ORR.References.[1] M. Li et al., Science, 354, 1414 (2016).[2] Z. Zhao et al., Adv. Mater.,31, 1808115 (2019).[3] M. Kato, Y. Iguchi, T. Li, Y. Kato, Y. Zhuang, K. Higashi, T. Uruga, T. Saida, K. Miyabayashi, I. Yagi, ACS Catal., 12, 259 (2022).[4] Y. Zhuang, Y. Iguchi, T. Li, Y. Kato, M. Kato, Y. A. Hutapea, A. Hayashi, T. Watanabe, I. Yagi, ACS Catal., 14, 1750 (2024).

Nano- and Mesoporous Structure Formation Probed with in Situ/in Operando Small and Wide-Angle X-Ray Scattering Analysis during Electrodeposition and Dealloying Processes

Electrochemical formation of nanoporous materials by electrodeposition or dealloying is essential in various fields such as catalysis, energy storage, and sensing due to their high surface areas and controlled pore sizes. Understanding the underlying principles leading to specific morphologies during the electrochemical protocol is of importance for a directed design of desired morphologies. In situ/in operando analysis at the nanoscale, such as grazing incidence small and wide angle X-ray scattering (GISWAXS), is an important tool to understand the pathway of the structure evolution at both the mesostructural and the crystalline levels. Here the development of a versatile electrochemical cell for GISWAXS [1] was essential to be able to investigate such processes.In this presentation an overview of various projects utilizing GISWAXS is given: (i) dealloying of the binary systems AgAu and CoPd [2]; electrodeposition of (ii) vertical aligned hexagonal Pt films using liquid crystal templating with Brij®56 [3]; and (iii) mesoporous platinum nickel films using Pluronic P123 as structure directing agent, as proposed by [4]. Additionally, some current highlights in the field of electrodeposition of ordered materials will be presented. M. Bogar, I. Khalakhan, A. Gambitta, Y. Yakovlev, H. Amenitsch, In situ electrochemical grazing incidence small angle X-ray scattering: From the design of an electrochemical cell to an exemplary study of fuel cell catalyst degradation. J. Power Sources. 477, 229030 (2020). Gößler, E. Hengge, M. Bogar, M. Albu, D. Knez, H. Amenitsch, R. Würschum, In Situ Study of Nanoporosity Evolution during Dealloying AgAu and CoPd by Grazing-Incidence Small-Angle X-ray Scattering. J. Phys. Chem. C. 126, 4037–4047 (2022). P.A. Wieser, D. Moser, B. Gollas., H. Amenitsch, Monitoring of Pore Orientation by in Operando Grazing Incidence Small-Angle X-ray Scattering during Templated Electrodeposition of Mesoporous Pt Films, Acs Appl. Materials and Interfieces 15, 47604-47614 (2023). K. Eiler, S. Surinach, J. Sort, E. Pellicer, Mesoporous Ni-rich Ni–Pt thin films: Electrodeposition, characterization and performance toward hydrogen evolution reaction in acidic media, Applied Catalysis B, Environmental 265, 118597 (2020). Fig. 1 (a) Scheme of the experimental setup for monitoring electrodeposition of mesoporous PtNi via in operando GISWAXS. The incoming X-ray beam impinges on the sample at a glancing angle αi (shown in the zoomed inset into the electrochemical cell). The scattering intensity is recorded simultaneously by two detectors: one in the direct beam, to study the GISAXS pattern during electrodeposition, and the other in the GIWAXS regime to resolve the diffraction pattern. (b) Chronoamperometric data during electrodeposition, performed under constant potentials at - 0.7 V vs AgCl. (c) Exemplary SEM micrograph of resulting mesoporous PtNi film. Figure 1

Simultaneous Production of Hydrogen and Chlorine from Brine with Pt-Loaded TiO2 Photocatalyst

Global warming caused by greenhouse gas emissions must be mitigated by switching from fossil fuels to renewable energy sources, which is a critical issue for modern society. Against this background, the use of particulate photocatalysts to convert solar energy from water to green and inexpensive H2 has attracted much attention.1 Freshwater is essential for ingestion and agriculture and is sometimes considered a valuable resource in developing countries and remote islands.2 Therefore, seawater and brine, which constitutes more than 97% of the water on Earth, are worth studying from this perspective.Seawater contains about 500 mM Cl– ion, which is involved in oxidation reactions. Cl– ion is oxidized to chlorine (Cl2), hypochlorous acid (HClO), and hypochlorite ion (ClO–) under acidic, neutral, and basic conditions, respectively. Therefore, the simultaneous production of H2 and Cl2 through photocatalytic seawater splitting is worth investigating as an economically and practically feasible system. In this study, we devised an overall brine splitting process for concurrently producing H2 and Cl2 with a particulate photocatalyst (Fig. 1(a)).Gas evolution reactions from brine at various pH under 365 nm light irradiation were monitored over time (Fig. 1(b))4. Under acidic condition (pH 1), H2 and Cl2 were preferentially produced, although a small amount of O2 was also produced. The e–/h+ ratio of the product, which was initially 3.4, decreased with time and eventually reached almost unity, indicating that the reaction proceeded stoichiometrically. Under neutral and basic conditions, H2 and a small amount of O2 occurred stably, while Cl2 and HClO were not detected by colorimetric measurements. Furthermore, the e–/h+ ratio of the final product in those scenarios was clearly not unity. This is likely due to photolysis of HClO or ClO–.The Pt-loaded TiO2 provided stable linear production of H2 and Cl2 for more than 10 hours under acidic conditions (Fig. 1(c)). After 14 h, the ClO– concentration exceeded 4 mM, a concentration sufficient for disinfection-related applications5. This result indicates that oxidation of Cl– ion occurred preferentially, even though O2 is thermodynamically easier to generate than Cl2. The apparent quantum yield of the overall brine splitting reaction in acidic media (about 0.6% at 365 ± 20 nm) is comparable to that previously reported for TiO2 photocatalytic water splitting reactions6. Furthermore, the calculated turnover number of H2PtCl6 (about 103) indicates that Cl2 was generated from the Cl– ion in solution. Thus, this result establishes the reliability of a new artificial photosynthesis system that can simultaneously produce H2 and Cl2 from brine.[1] J. Whitehead, P. Newman, J. Whitehead and K. L. Lim, J. Sustainable E arth Rev., 6, 1 (2023).[2] C. Klassert, J. Yoon, K. Sigel, B. Klauer, S. Talozi, T. Lachaut, P. Selby, S. Knox, N. Avisse, A. Tilmant, J. J. Harou, D. Mustafa, J. Medellı ́nAzuara, B. Bataineh, H. Zhang, E. Gawel and S. M. Gorelick, Nat Sustainability, 6, 1406-1417 (2023).[3] R. K. B. Karlsson and A. Cornell, Chem. Rev., 116, 2982-3028 (2016).[4] T. Okada, M. Korera, Y. Miseki, H. Kusama, T. Gunji, K. Sayama, Chem. Commun ., 60, 3299-3302 (2024).[5] E. W. Rice, R. M. Clark, C. H. Johnson, Emerging Infect. Dis., 5, 461–463 (1999).[6] K. Maeda, Chem. Commun., 49, 8404-8406 (2013). Figure 1

The Potential of Ruthenate Pyrochlores As Anodic Electroctalysts for PEM Water Electrolysisoral Presentation

Green hydrogen is becoming a hot commodity in the light of escalating oil and gas prices and their uncertain future availability. Among various electrolysis technologies, PEM water electrolysis (WE) is favorable for its portability, modularity, and the ability to integrate with intermittent, renewable energy sources. However, the upscaling of PEMWE is not feasible yet due to the need for rare and expensive metals as electrocatalysts. Specifically, iridium oxide is used as state-of-the art anodic electrocatalyst. Ruthenium oxide also has an excellent activity towards the anodic oxygen evolution reaction (OER), but is highly unstable. To address this limitation, this study investigates ruthenate pyrochlores as alternative anodic electrocatalysts. The pyrochlore structure may stabilize ruthenium. The pyrochlores in this study have been synthesized using a traditional citrate sol-gel method,1 as well as a novel combustion synthesis route. Physical characterization of the electrocatalysts has been conducted using x-ray diffraction (XRD), scanning (transmission) electron spectroscopy (S(T)EM) and Raman spectroscopy. Additionally, ex-situ electrochemical characterization has been performed in a three-electrode setup. Linear-sweep voltammetry results of Y2Ru2O7 synthesised via the citrate sol-gel route indicate an overpotential of 300 mV at a current density of 10 mA cm-2. This result agrees well with what has previously been reported for this electrocatalyst.2 Y2Ru2O7 synthesised via the novel combustion route performs better than the aforementioned due to increased surface area. Various A-site dopants have also been introduced into the pyrochlore structure to generate oxygen vacancies, modify the electronic structure and increase the stability. These materials have also been tested in a full-cell setup to gauge their performance for practical applications compared to state-of-the-art IrO2 and RuO2. References (1) Kim, J.; Shih, P.-C.; Tsao, K.-C.; Pan, Y.-T.; Yin, X.; Sun, C.-J.; Yang, H. High-Performance Pyrochlore-Type Yttrium Ruthenate Electrocatalyst for Oxygen Evolution Reaction in Acidic Media. J. Am. Chem. Soc. 2017, 139 (34), 12076–12083.(2) Feng, Q.; Zou, J.; Wang, Y.; Zhao, Z.; Williams, M. C.; Li, H.; Wang, H. Influence of Surface Oxygen Vacancies and Ruthenium Valence State on the Catalysis of Pyrochlore Oxides. ACS Appl. Mater. Interfaces 2020, 12 (4), 4520–4530.

Electrospun Pt Nanowires as a Highly Conductive Support for Ir for the Electrochemical Oxygen Evolution Reaction

The electrochemical Oxygen Evolution Reaction (OER) is a critically important reaction towards realizing a sustainable energy economy through the utilization of hydrogen as an environmentally friendly fuel. However, the relatively low conductivity of conventional IrOx catalysts hinders their performance and necessitates use of high Ir loadings.[1, 2] To counteract this insufficiency, utilizing highly conductive catalyst layer supports has become an effective strategy for maintaining optimal conductivity.[3-7] While they have allowed for improved stability, TiO2-based fibers typically possess poor conductivity. Thus, the inclusion of an additional components (Pt, Nb, Au, etc.) has been shown to improve the catalyst layer conductivity, thereby enhancing the OER activity for this class of catalyst.[8, 9] Herein, we utilize electrospinning as a method for producing conductive Pt-based nanowires with customizable porosity and diameter on the scale of tens of nanometers to be utilized as a support for active Ir-based catalysts. By controlling the electrospinning solution and operating parameters, the characteristics of as-spun Pt-CNFs may be controlled before high-temperature treatment to obtain Pt-NWs with regulated diameter.[10] Following the fabrication of Pt-NWs, we analyze the electrochemical performance and properties of the resulting Ir@Pt-NWs electrocatalyst.AcknowledgmentFinancial support from the Laboratory Directed Research and Development Program at Los Alamos National Laboratory through project 20240061DR is gratefully acknowledged.References Fu, C., et al., Metallic-Ir-based anode catalysts in PEM water electrolyzers: Achievements, challenges, and perspectives. Current Opinion in Electrochemistry, 2023. 38: p. 101227.Moriau, L., et al., Supported Iridium-based Oxygen Evolution Reaction Electrocatalysts - Recent Developments. ChemCatChem, 2022. 14(20): p. e202200586.Bele, M., et al., Towards Stable and Conductive Titanium Oxynitride High-Surface-Area Support for Iridium Nanoparticles as Oxygen Evolution Reaction Electrocatalyst. ChemCatChem, 2019. 11(20): p. 5038-5044.Bernsmeier, D., et al., Oxygen Evolution Catalysts Based on Ir–Ti Mixed Oxides with Templated Mesopore Structure: Impact of Ir on Activity and Conductivity. ChemSusChem, 2018. 11(14): p. 2367-2374.Chueh, L.-Y., et al., WOx nanowire supported ultra-fine Ir-IrOx nanocatalyst with compelling OER activity and durability. Chemical Engineering Journal, 2023. 464: p. 142613.Bernicke, M., et al., Tailored mesoporous Ir/TiOx: Identification of structure-activity relationships for an efficient oxygen evolution reaction. Journal of Catalysis, 2019. 376: p. 209-218.Karade, S.S., et al., IrO2/Ir Composite Nanoparticles (IrO2@Ir) Supported on TiNxOy Coated TiN: Efficient and Robust Oxygen Evolution Reaction Catalyst for Water Electrolysis. ChemCatChem, 2023. 15(4): p. e202201470.Regmi, Y.N., et al., Supported Oxygen Evolution Catalysts by Design: Toward Lower Precious Metal Loading and Improved Conductivity in Proton Exchange Membrane Water Electrolyzers. ACS Catalysis, 2020. 10(21): p. 13125-13135.Hu, W., S. Chen, and Q. Xia, IrO2/Nb–TiO2 electrocatalyst for oxygen evolution reaction in acidic medium. International Journal of Hydrogen Energy, 2014. 39(13): p. 6967-6976.Shui, J. and J.C.M. Li, Platinum Nanowires Produced by Electrospinning. Nano Letters, 2009. 9(4): p. 1307-1314. Figure 1

Inhibiting carbon corrosion of cobalt-nitrogen-carbon materials via Mn sites for highly durable oxygen reduction reaction in acidic media

Cobalt-nitrogen-carbon (CoNxC) materials are regarded as promising low-cost electrocatalysts for the oxygen reduction reaction (ORR). However, their susceptibility to deactivation and poor stability in acidic media limits their practical applications. In this study, we develop cobalt (Co) and manganese (Mn) embedded in nitrogen-doped carbon (CoMnNxC) dual-site catalysts by incorporating Mn into CoNxC and leverage a synergistic dual-catalysis strategy to optimize both activity and stability. The dynamic evolution of *OOH intermediate on the catalyst surface is monitored via in situ Raman spectroscopy, confirming that Mn introduction modulates the reaction pathway. Due to electron transfer from Mn to the Co-Nx center in CoMnNxC, *OOH activation on the surface is enhanced, and the two-electron ORR process is inhibited. Consequently, the CoMnNxC catalyst exhibits excellent ORR activity (E1/2 = 0.76 V vs. reversible hydrogen electrode) and a very low hydrogen peroxide (H2O2) yield (<2.9 %) in acidic electrolyte. Additionally, the dynamic evolution of *OH on the Mn-Nx site confirms that Mn-Nx can serve as a potential catalytic site for the hydrogen peroxide reduction reaction (HPRR), facilitating H2O2 decomposition. Differential electrochemical mass spectrometry (DEMS) demonstrates that this parallel catalytic pathway effectively weaks the oxidative corrosion of H2O2 on the carbon carrier. The results indicate that the negative half-wave potential shift of CoMnNxC catalysts in acidic electrolyte after 10,000 accelerated durability tests (ADT) is only 11 mV. The synergistic dual-catalytic strategy proposed in this work offers a novel approach for designing high-efficiency and stable transition metal-nitrogen-carbon catalysts.

Free‐Base Octaethylporphyrin on Au(111) as Heterogeneous Organic Molecular Electrocatalyst for Oxygen Reduction Reaction in Acid Media: An Electrochemical Scanning Tunneling Microscopy and Rotating Ring‐Disc Electrode Analyses

The oxygen reduction reaction (ORR) using metal porphyrin catalysts is currently widely explored. Conversely, metal‐free molecular systems are much less investigated, and there is limited information available for molecules such as nonmetalated macrocycles capable of catalyzing the ORR or other small molecules. Herein, the activity and selectivity of a heterogeneous organic molecular electrocatalyst, octaethylporphyrin (H2OEP), adsorbed on Au(111) toward ORR in acidic aqueous electrolyte are investigated. Electrochemical scanning tunneling microscopy (EC‐STM) is employed to monitor the molecular layer during the electrochemical process. Additionally, cyclic and linear sweep voltammetries are performed at still and rotating Pt/ring‐H2OEP‐functionalized Au(111)/disk electrodes to determine the activity and selectivity of the H2OEP monolayer toward ORR on Au(111). Based on EC‐STM and computation analysis, dioxygen electroreduction does not follow an inner‐sphere electron transfer reduction as seen in metal porphyrins, where a preliminary MO2 bond has to form, but it follows an outer‐sphere mechanism involving the precoordination of O2 induced by the protonated hydrogen of the macrocycle cavity.

Enhancing oxygen reduction reaction in acidic medium: A novel electrocatalyst of Pt–Co embedded in nitrogen-rich carbon nanosheets derived from polypyrrole-g-C3N4

Enhancing oxygen reduction reaction in acidic medium: A novel electrocatalyst of Pt–Co embedded in nitrogen-rich carbon nanosheets derived from polypyrrole-g-C3N4

Comprehensive theoretical study of the effects of facet, oxygen vacancies, and surface strain on iron and cobalt impurities in different surfaces of anatase TiO2.

We report the results of systematic ab initio modelling of various configurations of iron and cobalt impurities embedded in the (110), (101), and (100) surfaces of anatase TiO2, with and without oxygen vacancies. The simulation results demonstrate that incorporation into interstitial voids at the surface level is significantly more favourable than other configurations for both iron and cobalt. The calculations also demonstrate the crucial effect of the facet as well as the lesser effects of other factors, such as vacancies and strain on the energetics of defect incorporation, magnetic moment, bandgap, and catalytic performance. It is further shown that there is no tendency towards the segregation or clustering of impurities on the surface. The calculated free energies of the hydrogen evolution reaction in acidic media predict that iron impurities embedded in the (101) surface of anatase TiO2 can be a competitive catalyst for this reaction.

The Swiss Army Knife of Electrodes: Pillar[6]arene-Modified Electrodes for Molecular Electrocatalysis Over a Wide pH Range.

Molecularly-modified electrode materials that maintain stability over a broad pH range are rare. Typically, each electrochemical transformation necessitates a specifically tuned system to achieve strong binding and high activity of the catalyst. Here, we report the functionalisation of mesoporous indium tin oxide (mITO) electrodes with the macrocyclic host molecule pillar[6]arene (PA[6]). These electrodes are stable within the pH range of 2.4-10.8 and can be equipped with electrochemically active ruthenium complexes through host-guest interactions to perform various oxidation reactions. Benzyl alcohol oxidation serves as a model reaction in acidic media, while ammonia oxidation is conducted to assess the systems performance under basic conditions. PA[6]-modified electrodes demonstrate catalytic activity for both reactions when complexed to different guest molecules and can be reused by reabsorption of the catalyst after its degradation. Furthermore, the system can be employed to perform subsequent reactions in electrolyte with varying pH, enabling the same electrode to be utilised in multiple different electrocatalytic reactions.

The Swiss Army Knife of Electrodes: Pillar[6]arene‐Modified Electrodes for Molecular Electrocatalysis Over a Wide pH Range

AbstractMolecularly‐modified electrode materials that maintain stability over a broad pH range are rare. Typically, each electrochemical transformation necessitates a specifically tuned system to achieve strong binding and high activity of the catalyst. Here, we report the functionalisation of mesoporous indium tin oxide (mITO) electrodes with the macrocyclic host molecule pillar[6]arene (PA[6]). These electrodes are stable within the pH range of 2.4–10.8 and can be equipped with electrochemically active ruthenium complexes through host–guest interactions to perform various oxidation reactions. Benzyl alcohol oxidation serves as a model reaction in acidic media, while ammonia oxidation is conducted to assess the systems performance under basic conditions. PA[6]‐modified electrodes demonstrate catalytic activity for both reactions when complexed to different guest molecules and can be reused by reabsorption of the catalyst after its degradation. Furthermore, the system can be employed to perform subsequent reactions in electrolyte with varying pH, enabling the same electrode to be utilised in multiple different electrocatalytic reactions.

The influence of acetone and isopropanol crossover on the direct isopropanol fuel cell

Liquid organic hydrogen carriers (LOHC) offer a promising option to store and release hydrogen on demand within existing infrastructure. The direct isopropanol fuel cell (DIFC) uses the electrochemical acetone/isopropanol LOHC couple and combines the advantages of high fuel energy density at ambient conditions with CO2-free direct electricity production. Like other alcohol fuel cells, the DIFC combines two kinetically slow reactions, the isopropanol oxidation reaction (IOR) and the oxygen reduction reaction (ORR), requiring considerable overpotentials to drive the reactions. Accordingly, deconvoluting kinetic characteristics in the full cell is difficult. Therefore, this work uses the electrolytic electrochemical dehydrogenation unit (EDU), consisting of the IOR and the kinetically fast hydrogen evolution reaction in acidic media. This EDU then serves as an IOR full-cell model to get insights on the DIFC. Correspondingly, the demonstrated work is a comparison study investigating in-house fabricated catalyst-coated membrane electrode assemblies as hydrogen fuel cells, DIFC, and EDU. It investigates characteristic features of the DIFC and demonstrates how the acetone and isopropanol crossover affect the cathode of the DIFC.

Study of Kazakhstan’s Shungite as electrocatalyst substrate in hydrogen evolution reaction in acidic media

Study of Kazakhstan’s Shungite as electrocatalyst substrate in hydrogen evolution reaction in acidic media

Micelle-assisted electrodeposition of mesoporous PtCo nodular films and their electrocatalytic activity towards the hydrogen evolution reaction in acidic media

Hydrogen has received extensive attention in the energy field due to its high energy density and environmental friendliness. However, the large overpotential and slow kinetics limit the development of green water electrolysis technology. Rational design and construction of efficient and economical electrocatalysts are essential for sustainable hydrogen production. In this work, mesoporous PtCo films are successfully prepared by micelle-assisted electrodeposition using Pluronic F127 as a soft template. The optimal electrodeposition conditions of the film such as temperature and potential are determined. The composition of the films can be adjusted with the deposition potential to a Co content up to 45 at.%. The mesoporosity is clearly present at T=45 °C and E= − 0.6 V with a pore diameter of around 5–10 nm. The mechanism for the mesoporous PtCo films is proposed and the electrocatalytic activity in H2SO4 is evaluated. Mesoporous PtCo film with 45 at.% Co exhibits excellent electrocatalytic hydrogen evolution performance over commercial Pt/C, with an overpotential of − 22 mV at a current density of − 10 mA cm−2, and exhibits remarkable durability in the 24 h long-term aging stability test.

Engineering Ag3PO4/SnS2 heterojunction composite: A promising electrocatalyst for hydrogen evolution reaction in acidic medium

A Ag3PO4/SnS2 heterojunction composite electrocatalyst was fabricated using combined facile liquid exfoliation and hydrothermal technique by varying the concentration of SnS2 in Ag3PO4. Tin disulfide (SnS2) is a transition metal dichalcogenide that is a promising non-precious catalyst for hydrogen evolution reaction (HER) application. However, the practical application of this material is limited due to its poor electrical conductivity, to overcome this limitation it is made as a composite with Ag3PO4 as a n-type semiconductor which function by absorbing visible light with its suitable bandgap. The HER is evaluated through the three-electrode electrochemical set-up, where the catalyst coated on carbon cloth serves as a working electrode along with Ag/AgCl and platinum wire as reference and counter electrode respectively. The electrocatalyst is considered as best when it has certain criteria including lesser value of overpotential implying low current requirement to produce hydrogen. The catalyst should obey the following criteria like low resistance, high conductive nature, smaller exchange current density and has large surface area to actively participate in the electrochemical reaction. Apparently Ag3PO4/5 wt% of SnS2 is found to be the best performing composite as evidenced from the experimental data. This work may be useful for heterojunction composite catalyst for the practical application in electrochemical water splitting.

Robust self-supporting MoS2@Ni2B-GO/CNT electrode for enhanced hydrogen evolution reaction in acidic medium

Molybdenum sulphide (2D-MoS2) promises great potential as a hydrogen evolution (HER) catalyst, especially, when combined with conductive carbon supports like graphene oxide (GO) and carbon nanotubes (CNT). However, the hydrophobic nature of these carbon supports limits the catalytic potential of MoS2. To overcome this, we introduced hydrophilic Nickel Boride (Ni2B) into GO/CNT electrodes (Ni2B-GO/CNT), enhancing wettability (Contact angle-25.3°) and HER activity. By hydrothermally depositing MoS2 onto the hydrophilic Ni2B-GO/CNT electrode, we fabricated a self-supporting MoS2@Ni2B-GO/CNT electrode. The MoS2 deposition led to the formation of MoS2@Ni2B-GO/CNT heterostructure with multiple interfaces, favoring interfacial electronic redistribution (XPS) to significantly improve the HER activity. Thus, the proposed MoS2@Ni2B-GO/CNT electrode exhibited an excellent durability of 100 h (97%) and an overpotential of 224 mV at 10 mA cm−2 in acidic medium.

Electrodeposited manganese carbonate as an electrocatalyst for hydrogen evolution reaction in acidic medium

The electrolysis of water is the key method for hydrogen production but the high overpotential necessitates electrocatalysts. Traditionally, Pt is used, but it is scarce and costly. Herein, MnCO3 is unveiled as an electrocatalyst for the production of hydrogen. MnCO3 is electrodeposited onto pencil graphite by chronoamperometric method and confirmed by XRD and vibrational spectroscopic studies. MnCO3 electrodeposited for 15 min at 2 V demonstrates a good HER activity (overpotential of 123 mV to reach 10 mA cm−2) in 0.5 M H2SO4 with a Tafel slope of 79 mV dec−1. In addition, MnCO3 exhibited good stability during continuous operation (over 3000 cycles and 14 h). Though MnCO3 requires higher overpotential than the benchmark catalyst (Pt/C) to reach 10 mA cm−2, it outperforms Pt/C at higher current density (≥75 mA cm−2) demonstrating that MnCO3 could be used as an electrocatalyst to produce H2 at a high rate from acidic medium.

(Invited) Structural Transformations of OER Catalysts during Activation and Operation

Electrocatalysis of the oxygen evolution reaction (OER) plays a pivotal role in the hydrogen economy. Optimizing materials for this reaction presents a significant challenge, as many highly active materials exhibit low stability during activation and/or operation. Therefore, operando methods capable of probing catalyst structure and morphology become key tools for monitoring transformations during operation. These transformations not only determine activity but also influence long-term stability. In this context, high-energy X-rays provide a valuable probe, easily penetrating electrolytes and cell walls, offering unprecedented insight into material behavior. This contribution presents several classes of OER catalysts operating in alkaline and acidic environments, with their structural transformations studied using high-energy synchrotron scattering techniques.Layered double hydroxides (LDH) represent an important class of catalysts functioning in alkaline environments. Notably, NiFe and CoFe serve as exemplary materials due to their high activity and stability. However, in many cases, the structure during the OER reaction differs from the as-prepared materials, undergoing an α-phase to γ-phase transition, where the latter is the active phase. This transition, at times reversible with potential, is challenging to observe without high-energy wide-angle X-ray scattering (WAXS) techniques [1,2]. Another interesting example involves the origin of high activity in spinel-type Co3O4 thin film catalysts, elucidated by high-energy surface X-ray diffraction (HE-SXRD). Here, the superior performance is attributed to the formation of a 3D CoOx(OH)y active phase skin layer during activation, and its thickness defines the final activity [3].In the case of catalysts operating in an acidic environment, RuOx and IrOx are acknowledged as promising materials. While RuOx exhibits high activity, it is prone to instability, whereas IrOx, although stable, demonstrates lower activity and have significantly higher price. A prevailing trend is to create solid solution alloys of Ir and Ru to capitalize on the strengths of both materials [4]. This contribution details structural investigations of a series of IrRu alloys with varying compositions prepared through DC magnetron sputtering. The study investigates the unusual stability of these materials at high current densities using operando WAXS and a custom-built electrolyzer cell [5]. The findings reveal that these alloys undergo Ru dissolution upon activation, forming a thin amorphous IrOx layer that protects the alloy underneath. The stability is defined by this layer, while the activity is mainly determined by the electronic structure of the IrRu alloy core.The examples presented are a reminder that without operando characterization of the materials it is very difficult to ascribe origins of activity and stability, as the ex-situ characterization might be misleading regarding the structure and electronic structure of the active phase.[1] Dionigi, F. et al. In-situ structure and catalytic mechanism of NiFe and CoFe layered double hydroxides during oxygen evolution. Nature Communications, 2020, 11. https://doi.org/10.1038/s41467-020-16237-1[2] Dresp, S. et al., Molecular Understanding of the Impact of Saline Contaminants and Alkaline pH on NiFe Layered Double Hydroxide Oxygen Evolution Catalysts. ACS Catalysis, 2021, 11, 6800–6809. https://doi.org/10.1021/acscatal.1c00773.[3] Wiegmann, T. et al., OperandoIdentification of the Reversible Skin Layer on Co3O4 as a Three-Dimensional Reaction Zone for Oxygen Evolution. ACS Catalysis, 2022, 12, 3256–3268. https://doi.org/10.1021/acscatal.1c05169.[4] Galyamin, D. et al, Unraveling the Most Relevant Features for the Design of Iridium Mixed Oxides with High Activity and Durability for the Oxygen Evolution Reaction in Acidic Media. JACS Au, 2023, 3, 2336–2355. https://doi.org/10.1021/jacsau.3c00247.[5] Moss, A. B. et al., Versatile High Energy X-Ray Transparent Electrolysis Cell for Operando Measurements. Journal of Power Sources, 2023, 562, 232754. https://doi.org/10.1016/j.jpowsour.2023.232754.