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CeO2 decorated CoOx rod-like hybrid, supported onto holey reduced graphene (CoOx/CeO2/RGO) composite, was fabricated via a surfactant-assisted route. Its corresponding electrocatalytic performance towards oxygen reduction/evolution reactions (ORR and OER) was systematically investigated in alkaline electrolyte. Structural, morphological and compositional studies revealed changes in electronic and surface properties when CeO2 was introduced as an oxygen buffer material. The oxygen vacancies effectively enhanced the electrocatalytic activity, while the synergistic effect of co-catalyst CeO2, CoOx active-centers, and defective graphene with many voids facilitate the charge/mass transfer, making CoOx/CeO2/RGO an efficient and stable bifunctional electrocatalyst for OER/ORR with ΔE = 0.76 V (ΔE = E10 mA cm-2, OER – E1/2, ORR). This parameter is 70 mV and 270 mV lower than CoOx/RGO and the benchmark Pt/C, respectively. In addition, the OER/ORR bifunctionality of CoOx/CeO2/RGO composite outperforms that of Pt/C catalyst in a H2-O2 micro fuel cell platform.

Boron- and cerium-doped titania (Anatase) were prepared via sol-gel method. Phase composition and morphology were assessed by X-ray diffraction (XRD), scanning electronic microscopy (SEM), BET, diffuse reflectance spectra (DRS), and XPS. Photo-electrochemistry of these materials, deposited onto fluorine-doped SnO2 (FTO), was investigated in acid and acid-containing methanol. The boron-doped sample showed the best opto-electronic properties among the investigated samples. On the other hand, the cerium-doped titania samples annihilate to a certain extent the titania surface states, however, photogenerated charge separation was limited, and certainly associated to surface Ce3+/Ce4+ species. The substitutional effect of boron ions for O sites and interstitial sites was confirmed by XRD and XPS analyses.

Herein, FeCo bimetallic organic frameworks (MOFs) with different compositions were fabricated by controlling the initial molar ratio of Fe3+/Co2+ ions. Through a one-step carbonization treatment of FeCo MOFs and the melamine mixture, a series of FeCo nanoalloys encapsulated in bamboo-like N-doped carbon nanotubes (CNTs), entangled with N-doped carbon nanosheet nanocomposites (FexCoy–N–C), were prepared. The FexCoy–N–C materials presented an excellent ORR performance in alkaline medium. X-ray photoelectron spectroscopy (XPS) studies revealed the existence of ORR-active centers, such as Co–Nx, pyridinic-N and graphitic-N, which were responsible for the enhanced ORR activity. Besides, the synergistic coupling between FeCo alloy and N-doped carbon nanotubes favors the enhancement of the electrocatalytic performance. Among FexCoy–N–C electrocatalysts, the optimized Fe1Co3–N–C and Fe3Co1–N–C catalysts showed higher ORR performance. In addition, both Fe1Co3–N–C and Fe3Co1–N–C showed superior stability compared to the benchmark commercial Pt/C catalyst.

Carbon-supported palladium selenide (PdxSey/C) nanoparticles (NPs) were synthesized as oxygen reduction electrocatalysts for direct methanol fuel cells in an alkaline electrolyte. A simple chemical...

The performance of platinum group metal (PGM)-free bifunctional electrodes, in a regenerative H2/O2 microfluidic cell, is examined. The system is operated in an alkaline environment at 25 °C. Multiwalled carbon nanotube (CNT)-supported Ni-based nanostructures, NiO–Ni/CNT, were used to catalyze the hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR), whereas N-doped carbon nanohorn-supported NiFeOx–CoNy (NiFeOx–CoNy/NCNH) served as oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts. The system NiO–Ni/CNT||NiFeOx–CoNy/NCNH, at 25 °C, showed an interesting performance in fuel cell mode (ca. 15 mW cm–2 at the maximum peak) and in electrolyzer mode (ca. 102 mW cm–2 at 50 mA cm–2). The round-trip efficiency, after five consecutive operating cycles, decreased from 44.76 to 39.52%.

Carbon-supported PtM nanostructured materials (M = Cr, Co, Ni, Cu, Mo, Y, Sm, Gd) were investigated for the hydrogen evolution/oxidation reactions (HER/HOR) in alkaline medium. All catalysts were synthesized by the carbonyl complex chemical route. Among PtM, Cr, Co, Ni, and Cu formed nanoalloys. M2O3 was generated with Y, Sm, and Gd, and Mo was found at a dopant concentration of Pt. The electrochemical results showed that the HER/HOR activities on PtNi/C and PtCo/C outperformed that of the Pt/C benchmark. The presence of OHads species, acting as a bifunctional mechanism, favored the HER/HOR activity on PtNi/C and PtCo/C. This process is concomitant with early DFT studies that concluded that the presence of OHads weakens the Hads and H2Oads energetics.

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), namely, so-called oxygen electrode reactions, are two fundamental half-cell reactions in the energy storage and conversion devices, e.g., zinc–air batteries and fuel cells. However, the oxygen electrode reactions suffer from sluggish kinetics, large overpotential and complicated reaction paths, and thus require efficient and stable electrocatalysts. Transition-metal-based layered double hydroxides (LDHs) and their derivatives have displayed excellent catalytic performance, suggesting a major contribution to accelerate electrochemical reactions. The rational regulation of electronic structure, defects, and coordination environment of active sites via various functionalized strategies, including tuning the chemical composition, structural architecture, and topotactic transformation process of LDHs precursors, has a great influence on the resulting electrocatalytic behavior. In addition, an in-depth understanding of the structural performance and chemical-composition-performance relationships of LDHs-based electrocatalysts can promote further rational design and optimization of high-performance electrocatalysts. Finally, prospects for the design of efficient and stable LDHs-based materials, for mass-production and large-scale application in practice, are discussed.

Platinum nanoparticles (NPs) were photo-deposited on SnO2-C nanocomposites prepared by sol-gel method. Surface morphology of the prepared materials, examined by scanning electron microscopy (SEM) and transmission electron microscopy, confirmed selective deposition of Pt NPs on SnO2 nanoclusters formed on carbon surface. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) analysis, cyclic voltammetry (CV) and CO stripping experiments revealed modification of the electronic properties of the Pt NPs photo-deposited on the oxide-carbon composite in comparison to Pt/C prepared by the carbonyl chemical route. Rietveld refinement was employed to identify existing phases of catalysts and to determine the crystallite size. Micro-strain and intrinsic stacking fault increased and decreased, respectively, as a function of crystallite size. Pt loadings were determined by inductively coupled plasma mass spectrometry (ICP-MS). The oxygen reduction reaction (ORR) activity of the electrocatalysts was investigated in acid media using the rotating disk electrode (RDE) system. Accelerated durability test (ADT) results showed that photo-deposited Pt nanoparticles onto SnO2-C nanocomposite are more durable than those chemically deposited on carbon.

International audience; Manipulating the atomic structure of semiconductors is a fine way to tune their properties. The rationalization of their modified properties is, however, particularly challenging as defects locally disrupt the long-range structural ordering, and a deeper effort is required to fully describe their structure. In this work, we investigated the photoelectrochemical properties of an anatase-type structure featuring a high content of titanium vacancies stabilized by dual-oxide substitution by fluoride and hydroxide anions. Such atomic modification induces a slight red-shift band gap energy of 0.08 eV as compared to pure TiO 2 , which was assigned to changes in titanium− anion ionocovalent bonding. Under illumination, electron paramagnetic resonance spectroscopy revealed the formation of Ti III and O 2 − radicals which were not detected in defect-free TiO 2. Consequently, the modified anatase shows higher ability to oxidize water with lower electron−hole recombination rate. To further increase the photoelectrochemical properties, we subsequently modified the compound by a surface functionalization with N-methyl-2-pyrrolidone (NMP). This treatment further modifies the chemical composition, which results in a red shift of the band gap energy to 3.03 eV. Moreover, the interaction of the NMP electron-donating molecules with the surface induces an absorption band in the visible region with an estimated band gap energy of 2.25−2.50 eV. Under illumination, the resulting core−shell structure produces a high concentration of reduced Ti III and O 2 − , suggesting an effective charge carrier separation which is confirmed by high photoelectrochemical properties. This work provides new opportunities to better understand the structural features that affect the photogenerated charge carriers.

Flower-like hierarchical three-dimensional NiFe layered double hydroxides hollow microspheres (3D NiFe-LDH HMS), as one kind of novel non-noble metal electrocatalysts, have been fabricated in a template-free route for water oxidation. Both of the concentration of ammonium fluoride and the reaction time are adjusted to obtain a series of NiFe-LDH microspheres, with different internal structures from massive to hollow generated during the hydrothermal treatment, which improve the electrocatalytic activity of the NiFe-LDH catalysts towards the evolution reaction of oxygen. The optimized NiFe-LDH-0.4M HMS show the excellent OER performance in alkaline electrolyte with η = 290 mV@10 mA cm−2, and a Tafel slope of 51 mV dec−1, which outperforms the benchmark RuO2 catalyst. The possible reason is attributed to the more exposure of active sites, and fast ion transport resulting from the hierarchical hollow structure.

Direct ethanol fuel cells are highly promising energy conversion devices, but the complete oxidation of ethanol to CO2 at low temperatures is still one of the main challenges. Titanium oxycarbide (TiO1-xCx) powder is investigated as stable and synergistic support for Pt nanoparticles during the ethanol oxidation reaction (EOR) in acidic electrolytes. EOR products are quantitatively detected online with differential electrochemical mass spectrometry. At room temperature, Pt/TiO1-xCx has a CO2 efficiency maximum of 8.9%, while only 1.7% are measured for Pt nanoparticles on Vulcan carbon (Pt/C). The reaction pathway is channeled towards the formation of C1 products, while C2 product formation is suppressed. This effect is expected to be much enhanced at elevated temperatures which makes TiO1-xCx a highly interesting catalyst support material in general.

It is increasingly useful to develop bifunctional catalysts for oxygen reduction and oxygen evolution reaction (ORR and OER) for fuel cells, metal-air rechargeable batteries, and unitized regenerative cells. Here, based on the excellent conductivity and stability of ordered mesoporous carbons, and the best ORR and OER activity of Co3O4, the composite Co3O4/N-HNMK-3 was designed and manufactured by means of a solvothermal method, using ordered N-doped mesoporous carbon (N-HNMK-3) as substrate, and then the bifunctional electrocatalytic performance corresponding to ORR, OER in alkaline media was carefully investigated. The results showed that Co3O4/N-HNMK-3 composite, a non-precious metal centered electrocatalyst, displayed excellent ORR performance (activity, selectivity, and stability) close to that of commercial 20 wt.% Pt/C and a promising OER activity near 20 wt.% RuO2/C. The outstanding bifunctional activities of Co3O4/N-HNMK-3 was assessed with the lowest △E value of 0.86 V (EOER,10 mA cm&minus, 2-EORR,&minus, 3 mA cm&minus, 2) with respect to the two commercial precious metal-based electrocatalysts.

The recent advances in electrocatalysis for the hydrogen evolution reactions in acid and alkaline media are carefully reviewed. In this sense, this short review focuses on precious and non-precious catalytic centers. The recent development of HOR electrocatalysts with novel structures and compositions is highlighted. The understandings of the correlation between the activity and the shape, size, composition, and synthesis methods are summarized. The research directions, e.g., on the further development of more active, more stable, and less expensive electrocatalysts for the anion-exchange membranes for the alkaline fuel cell technology are provided. In this context, positive perspectives to overcome the high kinetic barriers encountered in alkaline medium can be expected in the years to come.

Structural degradation in manganese oxides leads to unstable electrocatalytic activity during long-term cycles. Herein, we overcome this obstacle by using proton exchange on well-defined layered Li2MnO3 with an O3-type structure to construct protonated Li2-xHxMnO3-n with a P3-type structure. The protonated catalyst exhibits high oxygen reduction reaction activity and excellent stability compared to previously reported cost-effective Mn-based oxides. Configuration interaction and density functional theory calculations indicate that Li2-xHxMnO3-n has fewer unstable O 2p holes with a Mn3.7+ valence state and a reduced interlayer distance, originating from the replacement of Li by H. The former is responsible for the structural stability, while the latter is responsible for the high transport property favorable for boosting activity. The optimization of both charge states to reduce unstable O 2p holes and crystalline structure to reduce the reaction pathway is an effective strategy for the rational design of electrocatalysts, with a likely extension to a broad variety of layered alkali-containing metal oxides., Structural degradation in manganese oxides leads to unstable activity during long-term cycles. Herein, authors demonstrated that reduced unstable O 2p holes and the short interlayer distance of layered lithium manganese oxide are favorable for excellent electrocatalytic stability and activity.

By combining experimental and theoretical aspects, this study focuses on exploring and enhancing the activity and stability towards oxygen reduction reaction (ORR) of fluorinated carbon supported platinum nanoparticles in the acidic electrolyte. Physical characterization results revealed that fluorinated carbon support generates a C-F bonding. The interaction between Pt and fluorinated-carbon allows for a strong charge transfer from Pt to the support. This phenomenon is consistent with the density functional theory (DFT) analysis. Because of the fluorination, the electronic structure of Pt is changed, which is an advantage for improving the catalytic activity and stability of the catalyst towards ORR.

Pt deposition/anchoring technique and nature of the support influence the oxygen reduction reaction (ORR) activity in low-temperature proton exchange membrane fuel cells. Surface distribution, morphology (particle shape and size) of the deposited Pt nanoparticles (NPs) and physicochemical properties contribute to the electrocatalytic activity and durability of the catalyst. Investigations over the past two decades lead to various metal and metal oxide-based supports, along with advanced nanocarbon materials as suitable candidates since they play a vital role in defining surface morphology, particle-size distribution, crystallinity and electronic structure of the deposited Pt catalyst. Moreover, such supports improve the ORR activity and stability of the electrocatalyst due to their stronger interaction with the deposited Pt NPs. Briefly, a well-controlled and selective deposition of Pt NPs and designing of an excellent corrosion-resistant support for a promising ORR catalyst has gained more attention. Many advanced strategies are developed for the fabrication of atomically precise nanostructured Pt catalysts. This review summarises recent developments in the electrochemical, photochemical and physical deposition techniques for Pt NPs on various supports and their effects on the physicochemical properties and electrocatalytic activity towards the ORR. Financial support by the Estonian Research Council (grant PRG723) and by the EU through the European Regional Development Fund (TK141, “Advanced materials and high-technology devices for energy recuperation systems”) is gratefully acknowledged. G.M. is grateful to CAPES-PrInt (grant 88881.311799/2018e01) for the financial support.

We report on a favorable synergy effect generated between molybdenum disulfide and different carbon supports. While MoSx species were generated by hydrolysis of [MoS4]2− in water, UV-light was employed to assist the MoS2 synthesis. It was found that the UV-assisted approach, combined with carbon supports properties, boosted the HER activity in acid solution. The synergy phenomenon between MoS2 and carbon supports was centered on sp3-like (C-defects) and sp2 domains of carbon of graphite powder (PG), multi-walled carbon nanotubes (CNT) or carbon Vulcan-XC-72 (C). The HER electrochemical kinetics on MoS2/CNT and MoS2/C proceeded via the Volmer-Heyrovsky mechanism. The stability and kinetic performance were attributed to the strong interaction between MoS2 and the surface nature of the carbon support.

A series of cobalt-based multicomponent electrocatalysts (Co-Cat-T) for the oxygen reduction reaction (ORR) were synthesized by thermal pyrolysis of activated carbon-supported cobalt and melamine mixture from 500 to 800 °C. Their corresponding electrocatalytic performance was systematically investigated toward ORR in an alkaline electrolyte. The electrocatalyst chemical composition and structure evolution (e.g., microstrain, crystallite size, and cell volume) were confirmed by X-ray diffraction Rietveld analyses. The material generated at 550 °C (Co-Cat-T550) showed the largest cell volume of the C

International audience; The use of high amounts of iridium in industrial proton exchange membrane water electrolyzers (PEMWE) could hinder their widespread use for the decarbonization of society with hydrogen. Nonthermally oxidized Ir nanoparticles supported on antimony-doped tin oxide (SnO2:Sb, ATO) aerogel allow decreasing the use of the precious metal by more than 70% while enhancing the electrocatalytic activity and stability. To date, the origin of these benefits remains unknown. Here, we present clear evidence of the mechanisms that lead to the enhancement of the electrochemical properties of the catalyst. Operando near-ambient pressure X-ray photoelectron spectroscopy on membrane electrode assemblies reveals a low degree of Ir oxidation, attributed to the oxygen spill-over from Ir to SnO2:Sb. Furthermore, the formation of highly unstable Ir(III) species is mitigated, while the decrease of Ir dissolution in Ir/SnO2:Sb is confirmed by inductively coupled plasma mass spectrometry. The mechanisms that lead to the high activity and stability of Ir catalysts supported on SnO2:Sb aerogel for PEMWE are thus unveiled.

The electrochemical characterization of chemical carbonyl route generated Pt:Ni nano-alloys, in acid and alkaline media, is reported. Earlier XRD and Debye Function Analysis (DFA) studies (Yang et al., 2004 [ 1 ]) provided the structure of these nanoalloys. Herein, the HER/HOR electrocatalytic activity as well as ORR kinetics, in alkaline medium, was determined and correlated with the interatomic Pt Pt distance. The HER/HOR and ORR exchange current densities describes a Volcano-like plot. For both systems, the maximum activity for both processes peaked with Pt3Ni.

Photoelectrochemical hydrogen production offers the possibility of direct conversion of solar energy to an energy carrier: hydrogen. While an attractive technology, the conversion rates and efficiencies observed to date are limited, making the technology non-feasible economically. In this chapter, we review the materials and reactors that have been used and reported for the purpose of photoelectrochemical water splitting.

Tailoring active, durable, and cost-effective electrocatalysts is crucial for hydrogen evolution (HER) and oxidation reactions (HOR) in an alkaline medium. Herein, the synthesis, physicochemical, a...

MOF(Ni/Fe) nanosheets were grown in situ vertically on three-dimensional (3D) nickel foam (NF). To induce a chemical coupling effect, defective CeO2-x nanoparticles (NPs) were chemically decorated on the surfaces of the MOF(Ni/Fe)/NF nanosheets. This phenomenon confirmed a positive effect for oxygen evolution in alkaline medium. The oxygen evolution reaction (OER) performance of the electrocatalysts reached an overpotential of ∼254 mV at j = 50 mA cm−2 with a Tafel slope of ∼34 mV dec−1.

The impact of sp2 sites of amorphous carbon and carbon nanotubes toward the hydrogen evolution/oxidation reactions on Pt nanoparticles, in alkaline medium, is described. The kinetic enhancement is given through the induced UV-photons of selectively photo-deposited platinum nanoparticles (Pt NPs) onto sp2 domains. The, henceforth, induced sp2 strong metal support interaction favors the electronic, and the oxophilic effects boosting the kinetics of hydrogen reactions.

Summary The phenomenon to restrain electrocatalytic particle agglomeration, while boosting the activity of multi-electron charge transfer reactions, known as strong-metal support-interaction, is reviewed. The main insights of this phenomenon are outlined. In this respect, the connection of a photo-induced process, to anchor metal centers, contributes to the electrocatalytic activity enhancement. Selected examples are given.