Amorphous Cu Intermediate Modification During Lewis Acid Etching of High-Entropy MAX to MXene Using CuCl2.

Electrochemical storage mechanism of interstratification-assembled Ti3C2Tx MXene/NiCo-LDHs electrode in alkaline, acid and neutral electrolytes

The rapid diffusion kinetics and smallest ion radius make protons the ideal cations toward the ultimate energy storage technology combining the ultrafast charging capabilities of supercapacitors and the high energy densities of batteries. Despite the concept existing for centuries, the lack of satisfactory electrode materials hinders its practical development. Recently, the rapid advancement of the emerging two-dimensional (2D) materials, characterized by their ultrathin morphology, interlayer van der Waals gaps, and distinctive electrochemical properties, injects promises into future proton-based energy storage systems. In this perspective, we comprehensively summarize the current advances in proton-based energy storage based on 2D materials. We begin by providing an overview of proton-based energy storage systems, including proton batteries, pseudocapacitors and electrical double layer capacitors. We then elucidate the fundamental knowledge about proton transport characteristics, including in electrolytes, at electrolyte/electrode interfaces, and within electrode materials, particularly in 2D material systems. We comprehensively summarize specific cases of 2D materials as proton electrodes, detailing their design concepts, proton transport mechanism and electrochemical performance. Finally, we provide insights into the prospects of proton-based energy storage systems, emphasizing the importance of rational design of 2D electrode materials and matching electrolyte systems.

Ceramic coatings were prepared on 6061 aluminum alloy using micro-arc oxidation (MAO) method in alkaline (pH = 11.3) and acidic (pH = 2.78) electrolytes, respectively. The MAO process was carried out in constant current mode using a unipolar pulse power supply. The voltage variation curves and discharge phenomena have been recorded during the process of MAO. For further comparison of the surface and cross-section microstructures, phase composition and corrosion resistance between the ceramic coatings produced in two different electrolytes, the scanning electron microscopy (SEM), x-ray diffraction (XRD), potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) were employed. It was found that there were great differences in the microstructures, and the discharge intensity in alkaline electrolyte was much stronger than that in acidic electrolyte. The coatings obtained in alkaline electrolyte were composed of Al2O3, while coatings fabricated in acidic electrolyte was composed of ZrO2 and Al2O3. Besides, the coatings prepared in acidic electrolyte showed better corrosion resistance than that in alkaline electrolyte due to the presence of ZrO2.

Morphology induced symmetrical supercapacitive performance of the 3D interconnected Ni(OH)2 framework

Sb2 O3 shows great promise as a high-capacity anode material for sodium-ion batteries (SIBs) due to the combined mechanisms of intercalation, conversion, and alloying. In this work, the electrochemical performance and mechanical property of Sb2 O3 nanobelts during sodiation/desodiation are revealed by constructing nanoscale solid-state SIBs in a high-resolution transmission electron microscopy. It is found that the Sb2 O3 nanobelt exhibits an ultrahigh sodiation speed of ≈13.5nm s-1 and experiences a three-step sodiation reaction including the intercalation reaction to form Nax Sb2 O3 , the conversion reaction to form Sb, and the alloying reaction to form NaSb. The alloying reaction is found to be reversible, while the conversion reaction is partially reversible. The Sb2 O3 nanobelt shows anisotropic expansion and the orientation of the Sb2 O3 nanobelt has great influence on the expansion ratio. It is found that the existence of a {010} plane with large d-spacing in the nanobelt leads to a surprisingly small expansion ratio (≈5%). The morphology of the Sb2 O3 nanobelt is well maintained during multiple electrochemical cycles. In situ bending experiments suggest that the sodiated Sb2 O3 nanobelts show improved toughness and flexibility compared to pristine Sb2 O3 nanobelts. These fundamental studies provide insight into the rational design of anode materials with improved electrochemical and mechanical performance in SIBs.

In situ characterizations of advanced electrode materials for sodium-ion batteries toward high electrochemical performances

Interfacial electronic interaction regulation of Rh2P by combining N, P co-doped graphene for boosting hydrogen evolution reaction

The development of fuel cells based on alkaline membranes (AMFCs) is one of the options to reduce the required amount of platinum, whereby the strong CO2sensitivity of alkaline membranes is a significant challenge. However, while there are several non-noble metal catalysts for the oxygen reduction reaction in alkaline electrolytes which match the activity of platinum, the only currently known hydrogen oxidation catalysts are based on platinum or palladium. Furthermore, the activity of platinum is orders of magnitude lower than in acidic electrolytes [1,2,3], so that ultra-low platinum loading anodes which can be used in acidic electrolytes (PEMFC) are not feasible in alkaline electrolytes. Therefore, the challenge to catalysis research for alkaline membrane fuel cells is to develop more active hydrogen oxidation catalysts. In our presentation, we will compare the kinetics of the H2 oxidation/evolution reaction (HOR/HER) on carbon supported platinum-group metal electrocatalysts in alkaline and acid electrolytes, determined by rotating disk electrode measurements in liquid electrolytes and hydrogen-pump measurements in fuel cells. The so far proposed causes for the »100-fold lower HOR/HER kinetics in alkaline electrolyte are an increased H/metal bond strength [1,4], a change of the reaction mechanism from H+ to H2O activation requiring more oxophilic catalyst surfaces [5], and/or a change of the water configuration at the metal/electrolyte interface [6]. The consistency of these hypotheses with the HOR/HER kinetics on different metal electrodes will be discussed.

Cetyltrimethylammonium bromide assisted intercalation and exfoliation for titanium carbide with enlarged interlayer spacing for high-performance supercapacitor

Electronically regulated FeOOH/c-NiMoO4 with hierarchical sandwich structure as efficient electrode for oxygen evolution and hybrid supercapacitors

Prussian blue analogs (PBAs) exhibit high energy density and a good electrochemical stability window in aqueous non-metallic ion batteries, which is conducive to achieving high energy output and stable operation. Additionally, their synthesis process is simple and environmentally friendly, meeting the demands of sustainable development. However, the poor conductivity, structural stability issues, and inadequate ion diffusion pathways limit their application in batteries. To overcome these challenges, researchers have adopted various optimization strategies: enhancing the conductivity of PBAs by compositing with high-conductivity carbon materials such as graphite, carbon nanotubes, or graphene; optimizing synthesis conditions such as temperature and reaction time to improve the defect and structural water content of PBAs, thereby enhancing their stability and electrochemical performance; employing surface modification techniques, such as conductive polymer encapsulation and acid etching, to improve their electrochemical stability and ion transport performance; and optimizing ion diffusion efficiency and battery kinetics by selecting suitable electrolytes and additives. These comprehensive measures contribute to improving the electrochemical performance of PBAs and promoting the development of their commercial applications. Based on prior research advancements, we introduce a novel synergistic regulation strategy: the creation of multi-redox-active centers to augment the transport capability of non-metallic ions and the optimization of defect structures through the establishment of a metal ion concentration gradient, thereby enhancing both electrochemical stability and performance.

Sustainable iron production is largely driven by the urgency to reduce the extensive energy consumption and emissions in the iron/steel sectors. Low-temperature electroreduction of iron oxide technology is thus revived since it directly utilizes (green) electrical energy with a competitive energy consumption compared to the thermochemical reduction approach. In the present work, we perform theoretical and experimental studies for comparison of electroreduction of iron oxide in aqueous alkaline and acidic electrolytes. Electrochemical reduction and deposition behavior are experimentally investigated using a lab-scale cell containing an electrolyte suspended with micron-sized Fe2O3 (hematite) powders. The effects of current density and hematite mass fraction on current efficiency are evaluated, as well as the total energy consumption. Results of chrono-potentiometry and cyclic voltammograms (CV) reveal the electrochemical properties of each system. The CV's cathodic peaks, corresponding to the reduction of iron oxides to iron, are observed only in the alkaline system where the iron oxide can be reduced at about −1.4 V (vs. Ag/AgCl). It is also found that the alkaline system has higher current efficiency (25–30% higher) and lower energy consumption (∼30% lower) than the acidic system. The cleaning of the deposit is also easier for the alkaline system, resulting in an iron product of high purity. Concerning the electrochemical performances and practicality, the alkaline electroreduction system shows promising potential for sustainable iron production.

Fuel cells and electrolyzers based on proton-exchange membranes (PEMs), operating at low pH (pH≈0), offer high power densities, but require large amounts of noble metal for the oxygen reduction reaction (ORR) in fuel cells and the oxygen evolution reaction (OER) in electrolyzers. For the hydrogen oxidation/evolution reaction (HOR/HER) only very small amounts of Pt is required due to its high activity for the HOR/HER.1 In alkaline electrolyte, non-noble metal catalysts are very active for the ORR and for the OER. Therefore, a replacement of the noble-metal intensive PEM technology by alkaline membrane technology seems promising. Unfortunately, for yet unclear reasons, the HOR/HER kinetics on Pt are much slower in alkaline than in acid electrolytes, and more active catalysts are needed to catalyze the HOR/HER in alkaline environment.2 It is therefore critical to elucidate the reasons for the poor HOR/HER activity of Pt in alkaline electrolytes, and this will be possible only by having a clear idea about the reaction mechanism and the rate determining step.Historically, the HOR/HER equilibrium has been described by invoking over potential deposited hydrogen, H-OPD, as the reactive intermediate species. 3 In contrast with adsorbed H intermediate present on noble metal surfaces at potentials positive to the reversible H+/H2 potentials in the process of the so-called underpotential-deposition (UPD), the believed reacting H-OPD species would form at potentials negative to the reversible H+/H2 potentials. So far, no clear evidence of the difference in the physical nature of H-OPD and H-UPD species has ever been reported. Recently, computational studies have addressed the HOR/HER rates by considering one of the three microscopic steps (Tafel, Volmer, Heyrovsky) as rate determining and only one state of adsorbed hydrogen species as reaction intermediate. 4 However, the link between this reacting adsorbed hydrogen intermediate and the H-UPD has never been explicitly stated.By comparing HOR/HER exchange current densities of carbon supported nanoparticles (Fig. 1) with the H-UPD charge transfer resistance (Fig. 2) which was determined by electrochemical impedance spectroscopy on polycrystalline surfaces (following refs.5 , 6) and, for the first time, on carbon supported nanoparticles, we will show that the H-UPD charge transfer rates closely match the HOR/HER exchange current densities in acid and alkaline electrolytes. Therefore, no H-OPD species has to be invoked to describe the two decades HOR/HER activity decrease from acid to base. This fundamental result gives credence to a HOR/HER rate controlled by the Volmer reaction.Moving away from the platinum system, iridium being an oxophilic surface is an interesting electrocatalyst system as it probes the hypothesis advanced by Strmcnik et al. that a more oxophilic surface might be effective in catalyzing the interaction with H2O/OH-, which they proposed to be the governing reaction in base. 7 However, our findings demonstrate explicitly that Ir does not have a higher activity than Pt in base (nor in acid). This leads to the conclusion that water dissociation is not the rate determining step in base, and, therefore, points toward identical microscopic HOR/HER reaction steps in acid and base.In conclusion, these novel insights confirm the H-binding energy as a relevant HOR/HER activity descriptor.8 Future studies will have now to address the pH effect on this binding energy and the synthesis of electrocatalysts with tuned H-binding energies.1. K. C. Neyerlin, W. Gu, J. Jorne and H. A. Gasteiger, J. Electrochem. Soc., 2007, 154, B631-B635.2. W. Sheng, H. A. Gasteiger and Y. Shao-Horn, J. Electrochem. Soc., 2010, 157, B1529-B1536.3. B. Conway and B. Tilak, Electrochim. Acta, 2002, 47, 3571-3594.4. E. Skúlason, V. Tripkovic, M. E. Björketun, S. Gudmundsdottir, G. Karlberg, J. Rossmeisl, T. Bligaard, H. Jónsson and J. K. Nørskov, J. Phys. Chem. C, 2010, 114, 18182-18197.5. K. Schouten, M. van der Niet and M. Koper, Phys. Chem. Chem. Phys., 2010, 12, 15217-15224.6. B. Łosiewicz, R. Jurczakowski and A. Lasia, Electrochim. Acta, 2012, 80, 292-301.7. D. Strmcnik, M. Uchimura, C. Wang, R. Subbaraman, N. Danilovic, D. Van der Vilet, A. P. Paulikas, V. Stamenkovic and N. Markovic, Nat. Chem., 2013, 5, 300-306.8. W. Sheng, M. Myint, J. G. Chen and Y. Yan, Energy Environ. Sci., 2013, 6, 1509-1512.

Self-assembled CoS/S-rGO dual-functional composite, and reliable hydrogen evolution performance in both acidic and alkaline media

Methanol oxidation in acidic and alkaline electrolytes using PtRuIn/C electrocatalysts prepared by borohydride reduction process