Proton exchange membrane water electrolysis (PEMWE) has emerged as one of the most promising technologies for large hydrogen (H 2 ) production from renewable electricity. However, using iridium (Ir) in large quantities is a roadblock in the widespread expansion of this technology. One strategy to reduce Ir loading in the anode is the use of an electroceramic support material. This study examines the structural and electrochemical evolution of Ir on antimony tin oxide (Ir/ATO) anodes under extended operation. Initial electrochemical performance demonstrates that low‐loaded Ir/ATO (0.2 mg Ir cm −2 ) can achieve a competitive current density of 2.82 A cm −2 at 2 V, comparable to state‐of‐the‐art PEMWE catalysts. However, extended operation leads to a minimal but gradual decline in catalytic activity. Postmortem analysis reveals changes in porosity and pore distribution, while atomic force microscopy (AFM) studies indicate ionomer degradation in the anode catalyst layer (ACL). Transmission electron microscopy (TEM) reveals the dissolution of oxides of Sb and Sn from the support material. Furthermore, X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption spectroscopy (XAS) confirmed the oxidation of metallic Ir (Ir 0 ) to IrOx x ·OH y species before and after operation. Understanding degradation in low‐Ir PEMWEs is key to improving long‐term stability. These results highlight the need for support stabilization and catalyst structuring to ensure durable performance.

Even though Ni-based catalysts are usually used for the anode and cathode in alkaline water electrolysis, their performance needs to be further enhanced. In the last few years exsolution of metal nanoparticles has emerged as a strategy to improve catalytic activity. However, few studies have used this strategy to improve the performance of electrocatalysts for alkaline water electrolysis. In this study, we report a highly active Ni-based electrocatalyst for the oxygen evolution reaction (OER) with ultra-low Ni loading, formed via Ni exsolution from La0.4Sr0.4Ti0.94Ni0.06O3-y. This work evaluates the effect of the calcination and the reduction temperature on the crystal structure, surface composition, oxidation state and OER performance. Rietveld refinement confirmed the successful Ni incorporation into the perovskite, and HRTEM and EDX reveal the formation of similar to 14 nm Ni/Ni-O nanoparticles on the surface after exsolution, which significantly enhances OER activity, achieving 2.1 mA cm(-2) at 1.6 V, compared to only 0.07 mA cm(-2) for the non-exsolved catalyst. The optimum electrocatalyst exhibits very high Ni-specific OER activity over 630 A g(Ni)(-1) at 1.65 V vs RHE. The optimum electrocatalyst showed good stability in an AEM cell at 500 mA cm(-2) and the cell potential remained steady at 2.12 V for 20 h. Therefore, this work proves the potential exsolution has as a strategy to improve the performance of mixed oxide for electrolysis in alkaline media.

The development of efficient, stable, and cost-effective bifunctional electrocatalysts, particularly those based on earth-abundant elements, is essential for the advancement and large-scale deployment of rechargeable zinc-air batteries (ZABs). In this study, we report the synthesis and electrochemical evaluation of FeMnOx-graphene composites as bifunctional catalysts for the oxygen reduction (ORR) and oxygen evolution reactions (OER). Three catalysts were prepared using a patented process by Gnanomat SL with different graphene nanoplatelets of different physicochemical properties and characterized through XRD, TEM, STEM-EDS, XPS, TGA, and BET analyses. All samples exhibited poor crystallinity and, according to XPS analysis, showed similar surface phases attributed to Fe2O3 or Fe3+ oxyhydroxide species and Mn3O4. Meanwhile, the graphene support influenced the final surface area and oxide dispersion of the composite. Electrochemical testing using a three-electrode system revealed that FeMn-graphene composites, synthesized with high-surface-area graphene, exhibit promising bifunctional activity for both the ORR and OER. Full-cell ZAB testing confirmed improved charge-discharge performance and excellent cycling stability over 500 h at 10 mA cm(-)2. These findings highlight the potential of FeMnOx-graphene composites as sustainable and efficient bifunctional air electrodes, providing an attractive alternative to bifunctional catalysts based on critical elements like Co.

This article presents the synthesis and evaluation of a novel double perovskite Dy2NiRu0.5Ir0.5O6, as a promising catalyst precursor for the oxygen evolution reaction (OER) in acidic electrolyte. In this perovskite, which was synthesised by a simple sol-gel process, there are two different B sites, one with Ni2+ atoms, and the other in which half of the Ir4+ atoms are replaced by Ru4+. Electrochemical measurements revealed an exceptional OER activity, with an Ir-normalised mass activity 5-7 times higher than the state-of-the-art IrO2 benchmarks. The catalyst also exhibited remarkable stability, maintaining a stable performance for at least 36,000 OER cycles. Structural and compositional analyses during cycling revealed a transformation of the pristine double perovskite structure into a 3D-hollow Ir0.9Ru0.1Ox framework. The reconstruction, which is driven by the dissolution of Dy3+, Ni2+ and part of Ru4+, results in a highly active and durable electrocatalyst. The enhanced OER performance is attributed to the composition and increased surface area of the reconstructed Ir0.9Ru0.1Ox hollow structure.

Renewable dimethyl ether (DME) can reduce the carbon footprint in LPG and transportation sectors. The direct synthesis of DME (DDMES) is attracting a great deal of attention because it is possible to increase the productivity of DME. However, DDMES is hindered by the formation of a high amount of water, which promotes the deactivation of both catalytic phases used in the DDMES, namely Cu/ZnO/Al2O3 and gamma-Al2O3. This is particularly relevant when CO2-rich syngas is used, since it leads to a higher production of H2O. In this work we show that heteropolyacids such as HSiW are a suitable alternative to state-of-the-art gamma-Al2O3 for the dehydration of methanol during the DDMES. This is because HSiW is not deactivated by the presence of water in the reaction medium. Thus, catalytic beds with HSiW reach up to four times higher DME productivity than those containing gamma-Al2O3. This feature is further exacerbated when water is removed from the reactor by means of a sorbent, i.e., during the sorption enhanced direct DME synthesis (SEDMES). Thus, the total carbon conversion is higher for SEDMES than for DDMES regardless of the actual nature of the acid catalyst.

Fe/N/C based catalysts are the best positioned ones to replace the state-of-the-art Pt-based catalysts for the oxygen reduction reaction (ORR) in Proton Exchange Membrane Fuel Cells (PEMFCs). Here, a Fe/N/C catalyst characterized by a high N/C ratio, has been synthesized from the pyrolysis of a N-rich imine-based polymer. In acidic electrolyte (0.1 M HClO4) the catalyst demonstrates notable ORR activity with Eonset and E1/2 values of 1.09 and 0.77 V vs. RHE, respectively. Furthermore, the catalyst's performance has been assessed in a single cell PEMFC setup. The optimization of the membrane electrode assembly (MEA) with the Fe/N/C catalyst entails examining various ionomer to catalyst ratios (I/C) as well as two coating methods: spray coating and drop casting. The optimized MEA achieved a cell performance of 725 mA cm-2 at 0.3 V and a power density close to 220 mW cm-2. In order to understand the factors influencing PEMFC polarisation curves, electrochemical impedance spectroscopy (EIS) was performed under potentiostatic conditions. The effect of operational parameters, such as ionomer to catalyst ratios (I/C) and the use of either O2 or air at the anode feed, has been investigated. EIS spectra allow the calculation of the distribution of relaxation times (DRT), providing insights into the rate and resistance of the ORR process occurring at the MEA. Notably, the cathode with an I/C= 2, prepared by drop casting, exhibited superior performance attributed to reduced ORR resistances. The current density and power density reached with the 25 cm2 MEA are comparable to those obtained with the 5 cm2 MEA using O2 as cathode reactant.

The conversion of carbon dioxide (CO2) to methanol offers a sustainable route to mitigate greenhouse gas emissions while producing a key chemical feedstock. In this study, we investigate the effect of magnesium (Mg) loadings on the performance of copper-based catalysts for CO2 hydrogenation to methanol. Catalysts based on Cu/ZnO/Al2O3 (CZA) were synthesized via co-precipitation and modified with varying amounts of Mg to yield Mg-promoted samples (CZAM). Comprehensive characterization using X-ray diffraction, N2adsorp-tion-desorption isotherms, H2temperature-programmed reduction, and N2O chemisorption revealed that moderate Mg incorporation decreases Cu crystallite size and enhances the BET surface area, thereby improving copper dispersion. Catalytic tests conducted at 240 degrees C and 50 bar with varying Gas Hourly Space Velocities (GHSV) showed that an intermediate Mg loading (approximately 0.8 wt%) yields optimal performance, achieving a CO2 conversion of 23.3 % and methanol selectivity of 55 %, comparable to that of a commercial catalyst. Excessive Mg content, however, adversely affects dispersion and selectivity despite higher intrinsic site activity. Stability tests over 120 h confirm sustained catalytic performance under reaction conditions. These results demonstrate that careful control of Mg loading and GHSV is critical to optimize catalyst structure and activity, offering insights for developing catalysts for sustainable methanol production from CO2.

ZrN and TiN thin coatings have been investigated for use on stainless steel for bipolar plates of proton exchange membrane water electrolyzers. Films were deposited by reactive magnetron sputtering using Ar and N2 from metallic Zr and Ti targets on different substrates to perform a deep characterization of their relevant properties. The effect of the deposition parameters, such as N2/Ar ratio, working pressure, or supplied power, has been explored. The structural, electrical, compositional, and optical properties of the films have been investigated by different techniques such as X-ray diffraction, 4-probe van der Pauw resistance, Rutherford backscattering, and optical reflectance and Raman spectroscopies, providing significant information about the films. Finally, after optimization of the preparation parameters to obtain suitable films, the electrochemical behavior of stainless steel coated by different films has been tested. The obtained corrosion current density for a ZrN/TiN/ZrN trilayer on mirror-polished AISI-304 stainless steel evidence their potential as electrodes in bipolar plates of proton exchange membrane electrolyzers.

The lack of stability of critical raw material-free electrocatalysts during the oxygen evolution reaction in acidic electrolytes lies beneath the use of Ir-based electrocatalysts in polymeric water electrolysis. Here, a strategy to enhance γ-MnO 2 stability in acid is proposed. Theoretical and spectroscopic approaches reveal that increasing the fraction of O atoms in the appropriate position, namely O pla , prevents Mn dissolution during water electrolysis.

A mixed oxide with the crystal structure of the DyMn 2 O 5 family, namely NdMn 1.5 Ru 0.5 O 5 , is reported active for the oxygen evolution reaction (OER) in acidic media. NdMn 1.5 Ru 0.5 O 5 displays high OER activity of 500 A g Ru- 1 at 1.5 V. Moreover, is more stable than most Ru oxides reported to date, remaining active for more than 500 cycles between 1.1. and 1.7 V at low scan rate of 10 mV s -1 . The high activity and stability are attributed to the Ru cations, as NdMn 2 O 5 exhibits very low OER activity. NdMn 1.5 Ru 0.5 O 5 has particularly short Ru - Ru distances of 2.60 & Aring;, a value close to the Ru - Ru metallic distances around 2.642 & Aring;. The high activity and durability of NdMn 1.5 Ru 0.5 O 5 for the OER are also demonstrated in a proton exchange membrane water electrolysis cell by producing a low -loaded anode electrode with 0.5 mg Ru cm - 2 . The cell achieves 1.97 V at 0.5 A cm -2 , consistent with the performances reported for Ru-based catalysts but with lower Ru loading. This performance is maintained during 100 h of operation. Additionally, NdMn 1.5 Ru 0.5 O 5 displays visible ORR activity in acidic media, recording an onset potential of 0.85 V at 0.1 mA cm -2 . It is noteworthy to highlight the extreme rarity of bifunctional ORR/OER catalysts acidic media.

EDITORIAL article Front. Chem. Eng., 18 March 2024Sec. Chemical Reaction Engineering Volume 6 - 2024 | https://doi.org/10.3389/fceng.2024.1396814

Developing cost-effective components for PEM electrolyzers is key to transforming renewable energy into H2. Platinum is a scarce and expensive material but also, is the most active known catalyst for hydrogen evolution reaction in PEM electrolysis; thus it is of utmost importance to focus on developing electrocatalysts that utilize the minimum amount of platinum without losses in cell performance to make PEM electrolysis affordable. In addition, and with the aim of scaling up electrode production, it is imperative to develop a robust automated industrial manufacturing process to avoid the waste of catalyst during electrode preparation. In this work, magnetron sputtering gas aggregation method is studied for developing three low loading Pt electrodes (0.105, 0.062, and 0.052 mg cm- 2), achieving remarkable overpotentials as low as 8 mV at 10 mA cm- 2 for HER, showing similar activity than commercial Pt electrodes with more than 4 times less Pt (compared to 0.3 mgcm- 2 Pt commercial GDL).

Single-Atom Catalysts (SACs) have emerged as the ultimate solutions in challenging systems bridging the gap between homogeneous and heterogeneous catalysts. However, feasible synthesis methods are necessary to stabilize single metal atoms, increase catalyst loadings and scale up the synthesis. Due to its sluggish kinetics, the oxygen reduction reaction (ORR) is the main source of irreversibility in proton exchange membrane fuel cells (PEMFC). The most promising candidates to replace Pt-based catalysts for the ORR in fuel cells are the so-called Fe-N/C catalysts. These catalysts display high ORR activity in acidic and alkaline electrolytes. In this work, we propose a laser-driven pyrolysis approach to generate Fe-N/C SACs that involves decomposition of aerosolized iron-phthalocyanines. The resulting catalyst displays ORR activity in acidic and alkaline electrolytes, with competitive half-potential and kinetic current density values in comparison with state-of-the-art electrocatalysts.

ABSTRACT Ni, Fe‐based nitrides have been widely studied for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media, displaying electrocatalytic activities similar to Pt and other noble metal electrocatalysts. The incorporation of small amounts of Mo or W on these Ni, Fe‐based nitrides is expected to have a significant effect on the electrocatalytic performance of these materials, especially for the HER activity. In this work, transition metal nitrides (TMNs) with the empirical formula Ni 1+ x Fe 3− x − y A y N (A = Mo, W), were obtained in two steps: synthesis of the transition metal oxide precursors by an easy, one‐pot sol–gel polymerization method followed by nitridation under ammonia atmosphere to obtain the final TMNs. Their HER and OER catalytic performances in alkaline electrolyte (0.1 M KOH solution) were studied and it was observed that the incorporation of small quantities of Mo or W in these Ni, Fe‐based nitrides (Ni 1+ x Fe 3− x − y A y N, where y = 0.1) results in improved HER and OER activities, especially in the TMN that contains W (i.e., Ni 1+ x Fe 2.9− x W 0.1 N), where the overpotentials were 348 mV for OER and 269 mV for HER. These values are lower than those obtained for Ni 1+ x Fe 3− x N, which are 395 mV for OER and 368 mV for HER.

Renewable dimethyl ether (DME) is expected to contribute to the decarbonization of several sectors, including domestic heat supply and transport. The shift of the carbon source used for the production of DME from fossil to renewable, such as biomass, waste or captured CO2, entails an industrial challenge in terms of reactors, operation regimes, catalysts and product purification, with strong technical and economic repercussions. In this work, we review the latest developments on this topic, focusing on the direct synthesis of DME, and especial attention has been paid to the separation-enhanced technologies for DME production, including the Sorption Enhanced DME Synthesis (SEDMES). We address other aspects that are often neglected, such as the impact of heat and mass transfer phenomena, which become increasingly relevant in processes in which several reaction and sorption stages occur in the same reactor. We also include a techno-economic section that gives insight in the feasibility of several renewable DME production processes. Finally, we review the most recently deployed installations for renewable DME production, at commercial or pilot scale, as a model of the near-future of the DME industry.

The development of cost-effective components for Proton Exchange Membrane (PEM) electrolyzers plays a crucial role in the transformation of renewable energy into hydrogen. To achieve this goal, two main issues should be addressed: reducing the Platinum Group Metal (PGM) content present on the electrodes and finding a large-scale electrode manufacturing method. Magnetron sputtering could solve these hurdles since it allows the production of highly pure thin films in a single-step process and is a well-established industrial and automated technique for thin film deposition. In this work, we have developed an ultra-low 0.1 mg cm−2 Pt loading electrode using magnetron sputtering gas aggregation method (MSGA), directly depositing the Pt nanoparticles on top of the carbon substrate, followed by a complete evaluation of the electrochemical properties of the sputtered electrode. These ultra-low Pt content electrodes have been thoroughly characterized and tested in a real electrolyzer cell. They demonstrate similar efficiency to commercial electrodes with a Pt content of 0.3 mg/cm2, achieving a 67% reduction in Pt loading. Additionally, durability tests indicate that these electrodes offer greater stability compared to their commercial counterparts. Thus, magnetron sputtering has been proven as a promising technology for manufacturing optimum high-performance electrodes at an industrial scale.

Ru mixed oxides may be suitable materials to replace state-of-the-art Ir-based catalysts in the anode of proton exchange membrane electrolyzers. To do this, the activity and especially the durability of Ru for the oxygen evolution reaction (OER) in acidic electrolyte should be improved. This work reports a family of Ru-based perovskites that combines both high activity and durability for the OER in acidic electrolyte. R2NiRuO6 double perovskites with R3+ = Pr3+, Nd3+, Tb3+, Dy3+, Y3+, Ho3+ and Er3+, and with Ni2+ and Ru4+ occupying B and B ' positions have been synthesized and evaluated for the OER in acidic electrolyte. The OER activities of R2NiRuO6 mixed oxides depend on the nature of R3+, with Dy2NiRuO6 displaying the highest activity (1.507 V at 10 mA cm(-2)) and being stable for more than 400 consecutive OER cycles measured at a slow scan rate. Characterization data indicate that the shorter Ru-O bonds in Dy2NiRuO6 are beneficial for the OER performance compared to the rest of the series. Computational modelling shows that Ru sites at pristine Dy2NiRuO6 are highly active for the OER, and their activity increases slightly upon Dy dissolution and progressively decreases as the local ratio of Ni to Ru is lowered.

The catalyst presented in this work can contribute to the development of the sustainable production of ethylene via bioethanol dehydration.

This work demonstrates novel in situ measurements of direct ethanol fuel cells (DEFCs), and shows that the syn-thesis procedure can exert a substantial influence over their activity, with exceptional activity demonstrated for a trimetallic PdAuNi/C catalyst prepared via NaBH4-2-propanol reduction (SBIPA). Furthermore, in situ Fourier transform infrared (FTIR) spectroscopy shows that the final ethanol electrooxidation reaction (EOR) over all catalysts investigated is acetate, thereby yielding valuable insights into the reaction mechanism. DEFCs present a sustainable net-zero technological solution which can supply diverse energy needs without increasing green-house gas (GHG) emissions. Ethanol can be produced from biomass precusors, and therefore its direct applica-tion in fuel cells can mitigate climate change and ensure environmental sustainability. In this work, PdAuNi/C catalysts are synthesized via three synthetic routes and applied in EOR. The catalysts are charachrterised via X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). Their electrocatalytic performance is evaluated by cyclic voltam-metry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). SBIPA exhibits excellent electrocatalytic results with an oxidation current peak of 9.6 A/mgPd. This is 4 times greater than that recorded for its monometallic counterpart prepared via the same procedure. It is, also, over twice as great as the other two trimetallic samples prepared by alternative protocols. Although adding Au and Ni to Pd signif-icantly enhances EOR activity, it does not increase the CO2 yield of EOR.

Abstract The production of green hydrogen in water electrolyzers is limited by the oxygen evolution reaction (OER). State-of-the-art electrocatalysts are based on Ir. Ru electrocatalysts are a suitable alternative provided their performance is improved. Here we show that low-Ru-content pyrochlores (R2MnRuO7, R = Y, Tb and Dy) display high activity and durability for the OER in acidic media. Y2MnRuO7 is the most stable catalyst, displaying 1.5 V at 10 mA cm−2 for 40 h, or 5000 cycles up to 1.7 V. Computational and experimental results show that the high performance is owed to Ru sites embedded in RuMnOx surface layers. A water electrolyser with Y2MnRuO7 (with only 0.2 mgRu cm−2) reaches 1 A cm−2 at 1.75 V, remaining stable at 200 mA cm−2 for more than 24 h. These results encourage further investigation on Ru catalysts in which a partial replacement of Ru by inexpensive cations can enhance the OER performance.