Galvanic replacement reaction (GRR), which arises from the difference in redox potential between two metal species in different oxidation states, is a powerful tool for designing structures with unique functionalities. However, extending GRR to more than two metals to target homogeneous structures remains puzzling. Here, we interrogated a single-step, low-temperature, convergent GRR strategy for assessing silver-platinum-palladium materials with tunable physicochemical and electrocatalytic properties. We synthesized carbon-supported silver (Ag/C, 19 wt %) using a solid-state carbo-reduction method. Then, silver atoms within Ag/C were engaged in GRRs with Pt(II)-Pd(II) species within a brine solution. Although thermodynamically favorable, the GRR between Ag(0) and Pt(II) requires a larger molar excess of Pt(II) than that between Ag(0) and Pd(II). We postulate that, in the presence of both metal precursors, the mechanisms of preferential replacement of silver atoms at the center of the particle by Pt(II) and homogeneous replacement by Pd(II) converge to produce porous architectures. Extensive characterization combined with glycerol electrooxidation and the oxygen reduction reaction (ORR) reveals the potential to drastically tune the electrocatalytic properties of the resulting materials by adjusting their electronic properties based on the amounts of Pt and Pd that enter and Ag that leaves the initial structure. This yields a low-loading trimetallic Ag/C_GRR-Pt+Pd electrocatalyst (3-9 wt % Pt+Pd) whose catalytic activity toward glycerol electrooxidation is twice that of bimetallics (Ag/C_GRR-Pt and Ag/C_GRR-Pd) and five to ten times that of state-of-the-art Pt/C and Pd/C electrocatalysts. The present knowledge could stimulate the exploration of complex GRR processes for designing medium- to high-entropy materials.

Traditional synthesis of organonitrogen compounds often requires high temperatures and pressures, contributing to greenhouse gas emissions and relying on costly noble metal catalysts. Electrosynthesis powered by renewable energy presents an alternative for C-N coupling reactions, though challenges remain in selectivity and mechanistic understanding. Here, we demonstrate that a molecular cobalt phthalocyanine (CoPc) complex immobilized on multiwalled carbon nanotubes (MWCNTs) efficiently catalyzes the co-electroreduction of CO and nitrite (NO2 -) to produce C-N coupling products with high selectivity. Our study reveals that formaldehyde (HCHO), generated from CO reduction, reacts with in situ produced hydroxylamine (NH2OH) from nitrite reduction to form formaldoxime (CH2=NOH) and methylamine (CH3NH2), achieving a total Faradaic efficiency exceeding 50%. Operando spectroscopy confirmed NH2OH as a key intermediate driving selective C-N bond formation. Extending this approach, we synthesized oximes like acetaldoxime and cyclohexanone oxime with similar to 70% Faradaic efficiency. This work offers a promising route for synthesizing diverse nitrogen-containing compounds.

Biosourced polyols such as ethylene glycol (EG) and glycerol (GL) have very high theoretical H2 storage capacity, of 8.15 wt% and 6.15 wt%, respectively. Moreover, both loaded and unloaded molecules display no or much lower toxicity, higher safety and are more environmentally-friendly (being also biodegradable), as well as cheaper than the classical LOHCs. Therefore, they could be excellent candidates as biosourced LOHCs, minimizing the risk during transportation. In addition, thermodynamic data indicate that these molecules can theoretically be oxidized from the very low potentials of ca. 0.11 V vs. RHE and ca. 0.27 V vs. RHE for GL and EG, respectively, with the release of hydrogen with electrical energy consumptions of ca. 20 kJ molH2-1 and ca. 53 kJ molH2-1, respectively, values lower or equivalent to that for classical LOHC. Then, several PtM/C and PdM/C catalysts were synthesized by a water-in-oil microemulsion method and characterized. Their behavior towards the GL and EG electrooxidation was followed by cyclic voltammetry, in situ infrared spectroscopy, and chronoamperometry with analysis of products by HPLC. The Pt9Bi1/C catalysts displayed the best activity and selectivity towards the formation of C3 and C2 oxidized compounds for GL and EG oxidation, respectively. For cell voltage <= 0.60 V vs. RHE, GL oxidation leads mainly to glyceraldehyde, then glyceric acid, tartronic acid and a small amount of formic acid. EG electrooxidation allows the formation of glycolic acid as main product, oxalic acid and an unidentified intermediate that is consumed when increasing the electrolysis time, but no formic acid. For these reasons, EG appears as the best candidate as LOHC.

Ni-based nanoparticles (NPs) were synthesized, deposited on a carbon support, and comprehensively characterised by TGA, (HR)TEM, XRD and XPS. The material comprises of core-shell NPs with a metallic Ni core and a sub-stoichiometric oxygenated Ni shell, with total size ranging between 5 and 30 nm, dispersed onto Vulcan XC72 carbon support (Ni@Ni(OxHy)/C). Electrochemical studies at different scan rates and formate concentrations indicate that formate is oxidized from ca. 1.30 V vs. RHE and that formate oxidation is a diffusion-limited reaction in the studied conditions. Results from EIS, in situ Raman and in situ infrared spectroscopy evidence the underpotential formate adsorption on Ni(OH)2 and NiOOH. The reaction is selective to carbon dioxide, which converts into carbonate ions because of the alkaline electrolyte. Moreover, formate oxidation seems to occur through a different pathway depending on the phase of nickel oxyhydroxide. The phase formed at lower potentials (beta-NiOOH) oxidises formate through a purely electrochemical pathway while the one (gamma-NiOOH) formed at higher potentials oxidises it through a catalytic electrochemical-chemical pathway, redox-mediated by the Ni (OH)2/NiOOH couple. Based on these findings, a reaction pathway is proposed for both phases.

Using a Pd(CeOx)/C catalyst prepared via a clean, water-based bromide anion exchange method, we successfully converted glycerol into glycerate. Compared to standard Pd/C, this catalyst, featuring palladium nanoparticles supported on carbon and modified with cerium oxide (CeOx), significantly enhances catalytic activity. The Pd(CeOx)/C catalyst achieved a 93% higher current density, and when used as an anode in a direct glycerol fuel cell, it delivered a 76% increase in power density and co-produced valuable glycerate. Transmission electron microscopy (TEM) revealed a uniform distribution of particles and a strong interaction between palladium and the cerium oxide, which enhanced the catalytic performance. Spectroelectrochemistry and high-performance liquid chromatography (HPLC) analyses confirmed the selective conversion of glycerol to glycerate regardless of voltage or CeOx modification. This selectivity is attributed to the elevated Pd d-band, which prevents C-C bond cleavage and favors C3 product formation. Interestingly, CeOx acted as a co-catalyst, improving Pd activity even though the Pd(CeOx)/C catalyst contains 40% less noble metal than the Pd/C catalyst.

Glycerol is a byproduct of vegetable oil transesterification and its overproduction has relegated this polyalcohol to the status of a low-value industrial waste. Glycerol electrooxidation can lead to various products such as glyceric, tartronic and glycolic acids, which have higher market prices than the starting molecule 1-4 . In order to enhance the electrocatalytic activity of Pt towards the oxidation of organic compounds, transition metals (TMs) are suggested. A new approach based on using co-catalysts with high affinity to oxygen as rare earth elements (RE), is also proposed 5 . Pt catalysts modified with REO x (RE = La, Ce, Nd, and Eu) or TMO x (Y) supported on carbon were prepared by a microwave-assisted polyol method. In the present work, the physico-chemical characterizations (TEM, XRD, TGA) of the synthesized materials will be presented. The behavior of these anode electrocatalysts in the presence of glycerol in a direct glycerol fuel cell will be explained. The role of the heterojunction as revealed by the TEM analysis will be discussed. After 4 hours of operation in fuel cell mode, glycerol was electro-oxidized in glycerate as the main product. The Pt(YOx)/C anode in which the Pt mass loading was reduced by 50% compared to Pt/C, exhibited a 38% higher power density (0.5 mW cm -2 ) and a current density of 4.5 mA cm -2 . References Li, T.; Harrington, D. A. An Overview of Glycerol Electrooxidation Mechanisms on Pt, Pd and Au. ChemSusChem 2021, 14, 1472-1495. Houache, M. S. E.; Hughes, K.; Safari, R.; Botton, G. A.; Baranova, E. A. Modification of Nickel Surfaces by Bismuth: Effect on Electrochemical Activity and Selectivity toward Glycerol. ACS Applied Materials & Interfaces 2020, 12, 15095-15107. Holade, Y.; Morais, C.; Servat, K.; Napporn, T. W.; Kokoh, K. B. Toward the Electrochemical Valorization of Glycerol: Fourier Transform Infrared Spectroscopic and Chromatographic Studies. ACS Catalysis 2013, 3, 2403-2411. Simões, M.; Baranton, S.; Coutanceau, C. Electrochemical Valorisation of Glycerol. ChemSusChem 2012, 5, 2106-2124. Corradini, P. G.; Hernandez, M. E. G.; de Morais, C.; Kokoh, K. B.; Napporn, T. W.; Perez, J. Rare-earth modified Pt-Sn catalysts obtained via bromide anion exchange for enhanced ethanol electrooxidation in alkaline medium. Journal of Solid State Electrochemistry 2023, 27, 2659-2670. Acknowledgements. The authors thank Brazil-France CAPES/COFECUB program under project 914/18. The authors also thank the European Union, “Région Nouvelle-Aquitaine” and CNRS for their financial support.

High-entropy oxides (HEOx) constitute a new class of materials that have attracted increasing interest over the past decade. By incorporating multiple cations into a single crystalline lattice, they achieve high configurational entropy (ΔS config ). This high entropy, combined with the presence of oxygen vacancies, can significantly enhance the mobility of charge carriers, leading to improved catalytic performance. Moreover, these materials exhibit exceptional thermal, chemical, and structural stability, making them highly suitable for a variety of catalytic and functional applications [1] [2]. Despite these advantages, HEOx materials have been relatively unexplored, especially in the field of photoelectrocatalysis. In this study, (CoNiFeCuZn)WO 4 and (MgCuCoNiZn)O were synthesized using a top-down approach and thoroughly characterized using various techniques to investigate its structural and optical properties. Their electrocatalytic activity toward the oxygen evolution reaction (OER) was evaluated using cyclic voltammetry and linear sweep voltammetry (LSV), which revealed a relatively high catalytic performance. Moreover, the visible-light band gap of these materials strongly suggests their potential for solar-driven water splitting. Modeling and preliminary photocatalytic results further indicate the possibility of using these materials to generate H 2 under illumination, making them promising candidates for future sustainable energy conversion applications. References [1] B. L. Musicó et al. , “The emergent field of high entropy oxides: Design, prospects, challenges, and opportunities for tailoring material properties,” APL Mater. , vol. 8, no. 4, Apr. 2020, doi: 10.1063/5.0003149.[2] Y. Sun and S. Dai, “High-entropy materials for catalysis: A new frontier,” Sci. Adv. , vol. 7, no. 20, May 2021, doi: 10.1126/sciadv.abg1600. Figure 1 : (left), Schematic representation of water splitting by photocatalysis on HEO , (righ) LSV on (CoNiFeCuZn)WO 4 Figure 1

Nowadays, the development of efficient electrochemical energy storage and conversion systems has become a crucial research topic. For systems such as electrolyzers, the highest challenge is designing a sustainable, active and stable electrocatalysts for the reactions involved, particularly the oxygen evolution reaction (OER). Efficient proton exchange membrane water electrolyzers have been developed with the use of noble metals. Nevertheless, their high cost and scarcity hinder the widespread use of such systems. An interesting alternative approach is the anion exchange membrane water electrolyzer since it allows using non-noble metal-based catalysts that may be thermodynamically stable in alkaline electrolyte at high electrode potentials. Among these, sulfides are increasingly studied as catalysts for the OER 1 . Whereas the sulfide core is preserved, an (oxy)hydroxide shell is formed after the surface reconstruction occurring at potentials required for the OER, and constitutes the active phase 2 . However, the use of unsupported sulfides has two major drawbacks: (i) even if their conductivity is higher than that of oxides, it remains relatively low and ii) the lack of dispersion of the active phase. To address these issues, the use of a conductive support is often considered to improve both the conductivity and the dispersion of the active phase. A possible support is carbon but it is subject to corrosion at potentials required for the OER, resulting in a strong loss of activity over time. It is then essential to find alternative and stable supports in alkaline conditions at high potential. Among them, M n+1 X n T z MXenes, a two-dimensional family materials constituted of a transition metal (M), a p-block element (X) usually carbon or nitrogen and T terminal groups (T = OH, F, O), are promising alternatives 3 . In this context, non-noble metal-based sulfides supported on a Ti 3 C 2 T z titanium carbide MXene were studied in this work. Under high potential, the surface of this support in contact with the electrolyte is passivated by a titanium dioxide layer but the MXene core is preserved, thus ensuring a high electronic conductivity in the catalytic layer. To obtain the composite, the Ti 3 C 2 MXene was first synthetized using a LiF/HCl route 4 . Then, Ni x Co y S z nanoparticles with various Ni/Co atomic ratio were synthesized using a microwave-assisted polyol route in the presence of the MXene at different loadings to promote the heterogeneous nucleation of active phase onto the MXene surface. The obtained materials were characterized using various physico-chemical techniques (XRD, ICP-OES, SEM) in order to gain insight into their structure, composition and dispersion over the MXene surface. It was observed that the MXene structure is preserved after the deposition of the active phase. The latter consists of two cubic phases, namely Co 3-x Ni x S 4 and Co 9-x Ni x S 8 , and two hexagonal phases NiS (figure 1.a), their corresponding mass fraction depending on both the Co/Ni ratio and the content of MXene. ICP-OES results show that experimental Co/Ni and active phase/MXene ratios are in good agreement with nominal ones. Interestingly, the addition of Co to Ni-rich sulfides and the increase of the MXene content reduce the size of particles, as highlighted by the evolution of the width at half maximum of the XRD peaks. Finally, electrochemical experiments were carried out to assess the activity of catalysts toward OER in an alkaline electrolyte (purified KOH 1 mol L -1 ) (figure 1.b). The presentation will aim at correlating the apparent activity of the different catalysts with their physico-chemical properties and compositions. References: (1) Wang, M.; Zhang, L.; He, Y.; Zhu, H. Recent Advances in Transition-Metal-Sulfide-Based Bifunctional Electrocatalysts for Overall Water Splitting. J. Mater. Chem. A 2021 , 9 (9), 5320–5363. https://doi.org/10.1039/D0TA12152E. (2) El-Refaei, S. M.; Rauret, D. L.; Manjón, A. G.; Spanos, I.; Zeradjanin, A.; Dieckhöfer, S.; Arbiol, J.; Schuhmann, W.; Masa, J. Ni-Xides (B, S, and P) for Alkaline OER: Shedding Light on Reconstruction Processes and Interplay with Incidental Fe Impurities as Synergistic Activity Drivers. ACS Appl. Energy Mater. 2024 , 7 (4), 1369–1381. https://doi.org/10.1021/acsaem.3c03114. (3) Anne, B. R.; Kundu, J.; Kabiraz, M. K.; Kim, J.; Cho, D.; Choi, S.-I. A Review on MXene as Promising Support Materials for Oxygen Evolution Reaction Catalysts. Advanced Functional Materials 2023 , 33 (51), 2306100. https://doi.org/10.1002/adfm.202306100. (4) Benchakar, M.; Loupias, L.; Garnero, C.; Bilyk, T.; Morais, C.; Canaff, C.; Guignard, N.; Morisset, S.; Pazniak, H.; Hurand, S.; Chartier, P.; Pacaud, J.; Mauchamp, V.; Barsoum, M. W.; Habrioux, A.; Célérier, S. One MAX Phase, Different MXenes: A Guideline to Understand the Crucial Role of Etching Conditions on Ti3C2Tx Surface Chemistry. Applied Surface Science 2020 , 530 , 147209. https://doi.org/10.1016/j.apsusc.2020.147209. Figure 1

Currently, MXenes represent probably the widest family of 2D materials. They are obtained from the exfoliation of the A layer of bulk three dimensional nanolamellar M n+1 AX n MAX phases (where A is an element mainly from column 13 or 14 from the periodic table) [1]. Their formula is M n+1 X n T z where M is a transition metal and X is C and/or N, and their structure consists in M n+1 X n octahedra layers where n is an integer varying from 1 to 4, covered with terminal groups T (with T = OH, O, F and/or Cl), formed during the etching of MAX precursors [2], [3]. The wide range of possible substitutions in the M, X, and T sites leads to materials with tunable properties and applications (sensors, bio-medical applications, optoelectronic systems, energy storage, heterogeneous catalysis, ...) [4], [5]. For the last decade, MXenes have been especially used in electrocatalysis as (i) substrates due to their high electronic conductivity, hydrophilicity and the presence of terminal groups acting as anchoring points for the deposition of active phases or (ii) directly as active phases especially for hydrogen evolution reaction (HER) [6], the most efficient MXenes towards HER being Mo-based [7]. Though their reactivity has been extensively studied, their surface redox properties are still not fully understood which brings the need for an in-depth investigation. In this study, Mo 2 CT x MXenes have been synthetized from the chemical etching of Ga in Mo 2 Ga 2 C MAX-like phase employing hydrofluoric acid. In some cases, delamination of multilayers MXenes was performed using TBAOH as delaminating agent. According to the etching and delamination conditions, MXenes with various Mo/C atomic ratios were obtained ( i.e. , Mo vacancies formation). The physicochemical properties of the different synthesized materials were investigated using various techniques such as XRD, SEM, Raman spectroscopy, ICP-OES and XPS. The surface redox properties of these MXenes have been investigated in alkaline electrolyte by performing cyclic voltammetry experiments. In order to get insights on the dynamics of electrode/electrolyte interface, diverse electrochemical measurements were conducted, with several parameters ( e.g. , scan rate, potential limits, number of cycles, polarization time) being systematically varied. Through mathematical models, the surface redox properties of these MXenes have been first inspected and correlated to the physicochemical properties of the synthesized materials. It was further demonstrated that after intensive cycling, a modification of the redox properties occurs (Fig.1). This implies that the material presents a surface reconstruction, not documented in the literature so far. Outcomes of this work will contribute to a deeper electrochemical understanding of Mo-based MXenes, in particular regarding their stability and reactivity, while guiding the rational synthesis engineering of MXenes. References [1] Y. Gogotsi, « The Future of MXenes », Chem. Mater. , vol. 35, n o 21, p. 8767-8770, nov. 2023, doi: 10.1021/acs.chemmater.3c02491. [2] A. VahidMohammadi, J. Rosen, et Y. Gogotsi, « The world of two-dimensional carbides and nitrides (MXenes) », Science , vol. 372, n o 6547, p. eabf1581, juin 2021, doi: 10.1126/science.abf1581. [3] M. Benchakar et al. , « One MAX phase, different MXenes: A guideline to understand the crucial role of etching conditions on Ti3C2Tx surface chemistry », Appl. Surf. Sci. , vol. 530, p. 147209, nov. 2020, doi: 10.1016/j.apsusc.2020.147209. [4] Y. Gogotsi et B. Anasori, « The Rise of MXenes », ACS Nano , vol. 13, n o 8, p. 8491-8494, août 2019, doi: 10.1021/acsnano.9b06394. [5] M. Naguib, « MXenes: A rising star in the constellation of two-dimensional materials », Curr. Opin. Solid State Mater. Sci. , vol. 24, n o 1, p. 100809, févr. 2020, doi: 10.1016/j.cossms.2020.100809. [6] Z. W. Seh et al. , « Two-Dimensional Molybdenum Carbide (MXene) as an Efficient Electrocatalyst for Hydrogen Evolution », ACS Energy Lett. , vol. 1, n o 3, Art. n o 3, sept. 2016, doi: 10.1021/acsenergylett.6b00247. [7] L. Loupias et al. , « Guideline for synthesis and surface chemistry characterization of 2D Mo/Ti solid solutions based MXene. Application to hydrogen evolution reaction in alkaline media », FlatChem , vol. 43, p. 100596, janv. 2024, doi: 10.1016/j.flatc.2023.100596. Figure 1

Ball milling, an eco-friendly material synthesis route, was used to produce a Ti-based precursor from a mixture of metallic Ti and TiO2 powders to obtain a corrosion-resistant and conductive support for the oxygen evolution reaction in an alkaline medium. The obtained materials were subsequently impregnated with Ni and Fe salts before being thermally treated under hydrogen. Thanks to this synthesis route, composite materials consisting of a Ni- and Fe-containing active phase deposited onto a TiyOx substrate were obtained. The chemical nature of phases composing this precursor material directly depends on the Ti/TiO2 mass ratio. For a mass ratio of 50%, the Ti-based precursor (sample labeled Ti-50), initially composed of TiO2 and Ti hydride phases, is transformed, after impregnation with Fe and Ni salts and heat treatment under H-2, into a highly electron conductive Ti2O3 phase, leading to a high oxygen evolution reaction (OER) activity. The influence of active phase loading and the Ni/Fe atomic ratio on the OER activity was subsequently investigated by performing electrochemical experiments. Different physicochemical techniques (X-ray diffraction (XRD), transmission electron microscopy (TEM), and inductively coupled plasma-optical emission spectrometry (ICP-OES)) were performed to characterize the composition, structure, and morphology of the different composite catalysts in order to evidence a correlation between materials' properties and their electroactivity toward OER. The sample labeled 30 atom % NiFe (50-50)-Ti-50 sample (i.e, Ni/Fe isoatomic ratio and atomic percent of the Ni- and Fe-containing active phase of 30%) appears as the most efficient material, since an overpotential of only 310 mV is required to drive a current density of 10 mA cm(-2). A chronopotentiometry test was carried out to ensure the stability of electrochemical performances after a long-term use of 7 days. Finally, post-mortem Raman spectroscopy and TEM measurements were performed to inquire into surface restructuring phenomena affecting the nanoheterostructured catalyst under working conditions.

2D MXenes have gained an ever-increasing attention in various application fields owing to the combination of their layered structure with their excellent physico-chemical properties. MXene properties can be strongly tuned by modifying the M element in the Mn+1XnTx structure. Among them, Mo-based MXenes are beginning to be successfully explored in many areas. However, few studies dealt with the synthesis and characterization of the (Mo,Ti)n+1CnTx solid solutions. The aim is to understand their complex chemistry in terms of structure, microstructure and surface chemical composition and to compare them with those of mono-metallic Mo2CTx and Ti3C2Tx MXenes as well as parent MAX phases. Then, the potential of these materials as HER (hydrogen evolution reaction) catalysts is determined in alkaline medium, never done so far, and their activity is correlated with their surface chemistry. It is particularly shown that Mo2Ti2C3Tx MXenes are a credible alternative to Mo2CTx MXenes since the surface properties of both MXenes are similar while their composition is quite different. Indeed, the (Mo,Ti)n+1CnTx MXenes require lower temperatures and shorter time for the synthesis than for Mo2CTx MXenes, a great advantage from an industrial point of view. Finally, this study aims at providing a roadmap to carry out the synthesis and characterization of (Mo,Ti)n+1CnTx MXenes.

Using the bromide anion exchange (BAE) green method to obtain carbon-supported nanoparticles, Pt(LaOx)/C was successfully prepared under mild conditions. This material, containing LaOx species generated in situ during the synthesis, was efficiently used as an anode to perform glycerol oxidation in alkaline medium in batch mode and at room temperature. In a direct alcohol fuel cell (DAFC), this catalyst was able to boost the glycerol-to-glycerate conversion with a 49% selectivity and a 28% power density higher than the same system using a BAE-synthesized Pt/C anode. The increase in catalytic activity may be due to the interaction of LaOx with the Pt active sites, acting as a bifunctional electrode. Furthermore, when used as an anode in an electrolysis setup, the selectivity of glycerol toward glycerate increased up to 67%. In situ FTIR and HPLC analyses confirmed the formation of the value-added glycerol oxidation products.

A still unexplored class of heterostructured bifunctional catalysts for oxygen evolution (OER) and reduction (ORR) reactions is investigated: Ni-Fe sulfides deposited onto a N,S-co-doped zeolite-templated carbon (ZTC) substrate achieved upon the impregnation of a ZTC with thiourea and Ni and Fe precursors (Ni/Fe atomic ratio of 1). By heat-treating the impregnated ZTC substrate at 700 degrees C under N2 atmosphere the efficient bifunctional catalyst is generated. A difference of only 0.76 V is measured between the potential required to drive an OER current density of 10 mA cm-2 and the ORR half-wave potential. Using electrochemical measurements and physico-chemical characterizations, it is evidenced that OER activity results from the presence of a sulfide containing both Fe and Ni whereas the ORR activity originates from the N,S-doped ZTC substrate. The selectivity of the ORR process is improved through the presence of sulfide phases. Compared to more conventional carbon substrate such as N,S-co-doped reduced graphene oxide, high specific surface area ZTC favors high ORR performances. The functional ZTC material was further successfully implemented as bifunctional air electrode in a coin-type Zn-air battery.

The synthesis of supported multielement transition metal phosphides (TMPs) to exploit the synergistic interplay between electronic and geometric effects resulting from the presence of different metals in the material and the arrangement of heterogeneous atoms is pivotal for reducing metal content while offering multiple active sites. However, the integration of Ni, Co, and P, for example, into a nanostructured carbon network to develop self‐supporting NixCoyP bimetallic phosphides is limited by several factors, including the synthesis and the discrepancy between the crystal structure of the respective monometallic phosphides. Moreover, conventional synthesis of supported TMPs often separates nanoparticles, support and phosphidation steps, which do not allow tailoring of physical and catalytic properties via particle support, electronic and geometric interactions. Herein, an innovative solid‐state, ex situ phosphidation‐free approach tailored to synthesize a library of self‐supporting NixCoyP TMPs in N,S,P‐modified nanostructured carbon networks generated together with NixCoyP particles is presented. Extensive multivariate characterization validates the unique properties of NixCoyP bimetallic materials with enhanced electrocatalytic performance for the hydrogen evolution reaction and the selective electroconversion of biomass‐derived 5‐hydroxymethylfurfural (5‐HMF) to value‐added 2,5‐furandicarboxylic acid (FDCA) with 90–100% Faradaic efficiency. Overall, the synthesis expands the possibilities for tailoring the microstructure of supported TMPs for improved physical/catalytic properties.

AbstractGlycerol electro‐oxidation reaction was performed in an alkaline environment with an anion exchange membrane fuel cell (AEMFC) operating in bath mode at low Pt‐loadings. BAE‐synthesized Pt/C and PtCe/C nanostructured catalysts were used as anode materials during 4‐hour operation to selectively obtain 65 % and 41 % of glycerate as main product, respectively. The modification of Pt with Ce improved the catalytic activity of the Pt/C catalyst generating 30 % more energy density after 4‐hour operation by achieving a higher degree of glycerol oxidation in cogeneration with added‐value products confirmed by spectroelectrochemical (in situ FTIR) and liquid chromatography coupled with mass spectrometry (LC–MS) analyses. The bifunctional mechanism generated by the presence of Ce is used to explain the improvement in the catalytic activity of Pt/C, due to the properties of this rare earth element to adsorb oxygenated species (OH−) and promote oxidation. The cathode material was a polyol‐synthesized PdFe/C electro‐catalyst for ORR that presented impressive stability and tolerance to glycerol.

Pt-Sn/C has been widely reported as an anode catalyst in direct ethanol fuel cell (DEFC). However, this bimetallic catalyst often results in the production of a four-electron reaction product (acetate) instead of 12 electrons required for complete ethanol oxidation. In this work, a surfactant-free bromide anion exchange (BAE) method was used for the first time to prepare rare-earth (La, Ce, Pr, and Eu) modified Pt-Sn electrocatalysts for promoting the C-C bond cleavage. Among the synthesized nanomaterials, Pt-Sn-Ce/C exhibited the highest current density and good stability in alkaline medium. X-ray photoelectron spectroscopy (XPS) was used to analyze the surface properties of the synthesized materials and correlate them with electrochemical characterizations to enhance their activity towards ethanol oxidation reaction (EOR). The in situ Fourier transform infrared (FTIR) spectroscopy investigations provided evidence of similar EOR pathways for Pt-Sn and rare-earth modified bimetallic anodes. The presence of the cocatalysts promoted higher current density during the EOR, especially for Pt-Sn-Ce/C.

The electrochemical nitrogen reduction reaction (NRR) to produce NH3 is the most efficient, eco-friendly and cost-effective alternative to the Haber-Bosch process. It is crucial to investigate and develop electrocatalysts selective for NH3 synthesis. In recent studies, the Ti3C2 MXene has emerged as a highly promising electrocatalyst for the NRR process. In this work, we explore the effect of Zif-8 addition over MXene sheets in order to control the rate of hydrogen evolution reaction (HER). Despite the better result obtained for Zif-8@Ti3C2 (3.0 μg NH3 gcat-1 h-1 at -0.55 V/RHE), the ammonia produced when using Zif-8@Ti3C2 as cathode material is shown to be originated from nitrogen atoms contained in the Zif-8 structure instead of those of N2. The results shed light to the need to fully understand the N2 electroreduction process over N-containing electrocatalysts.

Transition metal sulfides (NiSx, MoSx and Ni0.5Mo0.5Sx) are synthesized and have their HER performance evaluated in three-electrode cell setup by applying LSV analyzes in 1 M KOH. XRD, Raman, TEM and XPS characterizations are applied aiming to correlate physico-chemical properties/electrocatalytic activity. It is evidenced a synergistic effect in which nickel oxide, present in the surface of Ni0.5Mo0.5Sx, accelerates the water dissociation, while molybdenum sulfide catalyzes the reduction of adsorbed hydrogen species. When physically mixed with Carbon Vulcan, Ni0.5Mo0.5Sx only needs 60 mV higher overpotential to achieve-200 mA cm-2 than 40% Pt/C. Furthermore, Ni0.5Mo0.5Sx activity is assessed in interaction with different ionomers (Nafion & REG; or Sustainion & REG; XB-7). It is shown by an exploratory study that, when Nafion & REG; is replaced by XB-7, the amount of ionomer and water to isopropanol volume ratio must be diminished in the ink formulation to, at least, maintain a comparable activity of the electrode material.& COPY; 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

AbstractForesee advanced and innovative strategies is a key approach and constitutes a cornerstone for accessing clean, affordable, and reliable energy to satisfy the world's increasing prosperity and economic growth. To this end, hydrogen energy technologies parade as promising sustainable solutions to the looming energy crisis at either the small or large industrial scale, which will enable to reduce significantly our dependence on conventional energy sources based on fossil fuels without increasing atmospheric CO2 levels. Water electrolysis with renewable energy is one of the best solutions to produce hydrogen without COx (CO and CO2) emissions. However, the practical realization of this elegant opportunity of paramount importance is facing several challenges, among which are: (i) the efficient design of cathode and anode catalytic materials exhibiting improved intrinsic and durable activity; (ii) the scale‐up of the system for the large‐scale hydrogen production through the electrochemical water splitting. This review puts these opportunities and challenges into a broad context, discusses the recent research and technological advances, and finally provides several pathways and guidelines that could inspire the development of groundbreaking electrochemical devices for hydrogen production. It also points out the materials design and preparation for the efficient electrochemical production of the molecular hydrogen in acidic and alkaline environments, from a simple electrolytic solution to the water splitting reaction, which is also considered in the process. Furthermore, the main technology keys for designing a reliable electrochemical system will be noticed.

A polyol-assisted solvothermal route is used to synthesize Ni x Fe y nanoalloys supported on a highly electron conductive 2D transition metal Mo2CT x MXene. Structural, morphological and chemical characteristics of the materials are determined using several physicochemical techniques. The MXene support allows not only the formation of a nanostructured metallic Ni x Fe y nanoalloys, but also favors the interfacial charge transfer for the oxygen evolution reaction (OER). The Ni x Fe y @Mo2CT x material with a Ni/Fe ratio of 2.66 leads to the outstanding activity for the OER with an amazingly low Tafel slope value of 34 mV dec−1 and a current density of 10 mA.cm−2 at a potential of only 1.50 V vs. reversible hydrogen electrode (RHE). In situ Raman experiments show that β-NiOOH formed by oxidation of the nanoalloys under positive scan, likely containing a very small amount of Fe, is the active phase for the OER. This material exhibits also an excellent stability over 168 h in a 5 M KOH electrolyte. Transmission electron microscopy -electron energy-loss spectroscopy analyses after 100 voltammetric cycles between 0.2 and 1.55 V vs. RHE evidence for the first time that the MXene support is not fully oxidized in the first cycle. Also, oxyhydroxide layer formed in the OER potential region at the surface of the Ni x Fe y nanoparticles can be reversibly reduced.