Long-term Electrochemical Stability Research Articles

Boosted Hydrogen evolution reaction based on synergistic effect of graphene, MoS2 and RuO2 ternary electrocatalyst

Hydrogen holds the promise of replacing fossil fuels and offers a sustainable pathway for energy generation. However, the large-scale production of hydrogen via the environment friendly electrocatalytic process relies heavily on the performance of electrocatalysts. In this study, we investigate the electrocatalytic performance of graphene nanosheets (GNS), molybdenum disulfide (MoS2), ruthenium dioxide (RuO2), and their composites for hydrogen evolution reaction (HER), a novel combination that has not been explored in previous literature. We synthesize the materials using Liquid Phase Exfoliation at 500 and 1000 RPMs for GNS and MoS2 and via hydrothermal methods for RuO2 nanosheets and nanoparticles, aiming to exploit synergistic effects for enhanced activity and stability. The synthesized GNS-1000/MoS2-1000/RuO2-NSs composite demonstrates promising HER results, showcasing a low overpotential of 63 mV and a reduced Tafel slope of 59 mV/dec. This improvement indicates enhanced electron transfer, improved active site dispersion, and increased surface area due to the synergistic effects, which also aids in long-term electrochemical stability. Our study underlines the potential of GNS/MoS2/RuO2 composites, particularly the GNS-1000/MoS2-1000/RuO2-NSs, in transforming hydrogen production methods and promoting efficient, sustainable energy solutions. The implications of our findings extend the boundaries of materials engineering, edging us closer to a sustainable energy future.

NiS2/NiS/Mn2O3 Nanofibers with Enhanced Oxygen Evolution Reaction Activity.

The development of efficient and cost-effective electrocatalysts is crucial for achieving a green hydrogen economy through electrocatalytic water splitting. Herein, we report an excellent catalyst, one-dimensional NiS2/NiS/Mn2O3 nanofibers prepared by electrospinning, which exhibits outstanding electrochemical performance in an alkaline solution. We explored effective strategies to construct one-dimensional nanostructures and composite oxides to promote the electrocatalytic performance of transition metal dichalcogenides. At a current density of 20 mA cm-2, it requires an overpotential of 333 mV for OER. Furthermore, NiS2/NiS/Mn2O3 nanofibers maintain good durability even after 1000 cycles. The long-term electrochemical stability test of the catalyst NiS2/NiS/Mn2O3 was implemented at 20 mA cm-2 for 12 h. The potential remained at 99.52%. Therefore, this study demonstrates that NiS2/NiS/Mn2O3 can serve as a viable green hydrogen production electrocatalyst.

Myrica rubra-like P–Co1-xS/C as an efficient catalyst for all-pH hydrogen evolution reaction

The development of cheap, efficient and stable hydrogen-producing catalysts is the current research focus, especially the catalysts that can work stably in the whole pH range. In this work, a myrica rubra-like structure of P–Co1-xS/C was synthesized by hydrothermal reaction, sulfurization and phosphorization using spherical flower-like cobalt glycerate (CoG) as precursor. The design of this multilevel structure of P–Co1-xS/C effectively increases the specific surface area. The doping phosphorus and the protection of carbon layer greatly improve catalytic performance and enhance the stability of Co1-xS in the hydrogen evolution reaction (HER) at full pH range. When the current density is 10 mA cm−2, the HER overpotentials of P–Co1-xS/C in acidic, alkaline and neutral solutions are 86, 93 and 167 mV, and respectively. The Tafel slopes of P–Co1-xS/C in acidic, alkaline and neutral solutions are 82, 100 and 103 mV dec−1, respectively. In addition, the electrocatalyst also displays excellent electrochemical long-term stability. After 2000 cycles or 20 h long-term testing, its catalytic activity remains stable without obvious decrease at full pH range.

Electrocatalytic Conversion of CH4 to High Value-Added Liquid Fuel over Binary Metal Oxide Tandem Catalysts

As the main component (> 85%) of combustible ice and shale gas, methane (CH4), plays a significant role in the greenhouse effect.(1) Although CH4 was widely used to synthesize high value-added Cx oxygenates via indirect industrial reforming with high-energy consumption. The accurate control of oxidation degree in CH4 conversion remains a great challenge.(2) Therefore, it is difficult to achieve high conversion rate and high selectivity at the same time. The convenience and reliability of the control of reaction potential, as one of the advantages of electrocatalysis technology, can effectively address the above problems.(1, 3) Electrochemical technologies of CH4-to-Cx oxygenates are regarded as one of the most attractive pathways to produce bulk industrial liquid fuels.(4) Especially in the premise of clean energy as an energy source, the electrochemical conversion of methane demonstrates very advantageous market potential. In this work, we prepared a ZrO2 modified FeOx binary metal oxides tandem catalyst to accelerate partial oxidation of CH4 under ambient condition. With CO3 2- as an oxidant, ZrO2@FeOx tandem catalyst shows remarkable CH4 conversion performance with large current density gap (13.65 mA cm-2) and long-term electrochemical stability (negligible attenuation (8 %) after 48 hours) in three-electrodes cell. In addition, in a flow reactor, ZrO2@FeOx-based electrode also exhibits a highly stable operating lifespan over 72 hours at a large current density 50 mA cm-2 and achieve a feasible CH4-liqid fuel conversion with high total faradaic efficiency.References F. Liu, Y. Yan, G. Chen and D. Wang, Green Chemistry, 26, 655 (2024).S. Yuan, Y. Li, J. Peng, Y. M. Questell-Santiago, K. Akkiraju, L. Giordano, D. J. Zheng, S. Bagi, Y. Román-Leshkov and Y. Shao-Horn, Advanced Energy Materials, 10, 2002154 (2020).M. R. A. Kishore, S. Lee and J. S. Yoo, Adv Sci (Weinh), 10, e2301912 (2023).L. Fu, R. Zhang, J. Yang, J. Shi, H. Y. Jiang and J. Tang, Advanced Energy Materials, 13 (2023).

High-Performance All-Solid-State on-Chip Planar Micro-Supercapacitors Based on Aminated Graphene Quantum Dots by Photolithography

Rapid development of portable miniaturized electronic devices has put forward higher requirements for microenergy. Functionalized graphene quantum dots combine the properties of both functionalized graphene and quantum dots, and are expected to promote further development of high-performance energy storage devices. Here, all-solid-state on-chip planar micro-supercapacitors (PMSCs) were fabricated based on aminated graphene quantum dots by modified liquid-gas interface self-assembly and photolithography, with the electrode width/gap of 24 μm/8 μm. The electrochemical performance was analyzed by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectrometry and cycle stability in PVA/H2SO4 gel electrolyte. The results indicated that the fabricated PMSCs showed good capacitive response at the scan rates of 0.01 V s−1 to 10000 V s−1. The CV curves of the PMSCs displayed a typical pseudocapacitive feature at the scan rates of 0.01 V s−1 to 1 V s−1. The PMSCs had ultrahigh rate capability of up to 10000 V s−1, and the GCD curves were near triangle-shaped curves, demonstrating excellent electrochemical reversibility. The PMSCs showed ideal capacitive behavior at the low frequency region of the Nyquist plot. The Nyquist plot of the PMSCs showed a semicircle at the high frequency region. The relaxation time constant of the PMSCs were 3.59 μs, indicating that the PMSCs had fast frequency response. After 10000 charge-discharge cycles at the scan rate of 500 V s−1, the initial capacitance retention rate of the PMSCs were 99.17%, indicating that the PMSCs possessed good long-term electrochemical stability. This study provides an important reference for the application of functional graphene quantum dots in the field of the PMSCs.

Investigation on Al3+ ion storage in Bi2MoO6 and Bi2WO6 for rechargeable aqueous aluminum-ion battery

Reversible and stable electrochemical Al3+ ion storage process defines the functioning of a rechargeable aluminum-ion battery. Herein, we illustrate the electrochemistry of Bi2MoO6 and Bi2WO6 for Al3+ ion storage in aqueous electrolyte. It was found that the electrochemical characteristics are quite dependent on the nature of the electrolyte. While the charge-discharge profiles are almost identical for both Bi2MoO6 and Bi2WO6, it is to be noted that Bi2WO6 exhibits better electrochemical long-term stability and severe capacity decline is noticeable for Bi2MoO6. The specific discharge capacity is 94 mAhg−1 at a current density of 1 Ag−1 over 50 cycles for Bi2WO6 in an optimized AlCl3 aqueous electrolyte. By adopting an optimized current collector, the specific capacity could be significantly enhanced to above 200 mAhg−1 at a current density of 1 Ag−1. A mechanistic study conducted through ex-situ XRD, XPS, Raman, FTIR, UV–Visible, FESEM and HRTEM reveals probable transformation of Bi2WO6 to BiOCl during the electrochemical process.

Enhancing P2/O3 Biphasic Cathode Performance for Sodium-Ion Batteries: A Metaheuristic Approach to Multi-Element Doping Design.

Sodium-ion batteries (SIBs) have emerged as a compelling alternative to lithium-ion batteries (LIBs), exhibiting comparable electrochemical performance while capitalizing on the abundant availability of sodium resources. In SIBs, P2/O3 biphasic cathodes, despite their high energy, require furthur improvements in stability to meet current energy demands. This study introduces a systematic methodology that leverages the meta-heuristically assisted NSGA-II algorithm to optimize multi-element doping in electrode materials, aiming to transcend conventional trial-and-error methods and enhance cathode capacity by the synergistic integration of P2 and O3 phases. A comprehensive phase analysis of the meta-heuristically designed cathode material Na0.76Ni0.20Mn0.42Fe0.30Mg0.04Ti0.015Zr0.025O2 (D-NFMO) is presented, showcasing its remarkable initial reversible capacity of 175.5mAh g-1 and exceptional long-term cyclic stability in sodium cells. The investigation of structural composition and the stabilizing mechanisms is performed through the integration of multiple characterization techniques.Remarkably, the irreversible phase transition of P2→OP4 in D-NFMO is observed to be dramatically suppressed, leading to a substantial enhancement in cycling stability. The comparison with the pristine cathode (P-NFMO) offers profound insights into the long-term electrochemical stability of D-NFMO, highlighting its potential as a high-voltage cathode material utilizing abundant earth elements in SIBs. This study opens up new possibilities for future advancements in sodium-ion battery technology.

Inducing energy storage: Bimetallic MOF-derived Co3O4/NiO nanocomposites for advanced electrochemical applications

Multimetallic-based nanocomposites have arisen as highly capable functional materials, offering new horizons for applications in electrochemical energy storage. Among the platforms for synthesizing a diverse range of nanostructures incorporating metals, oxides, sulfides, and nitrides within a porous carbon matrix, metal–organic frameworks (MOFs) stand out as exceptional candidates. In this study, we successfully synthesized Co3O4/NiO nanocomposites from a Co/Ni MOF, employing a 2-mthylimidazole (2 MI) linker as a key component in the synthesis process. The resulting nanocomposites reveal a notable synergy of characteristics, including high crystallinity, retained morphologies, and adjustable textural features, all of which are validated through a comprehensive series of characterization analyses. Leveraging these distinct advantages, the primary objective of this research is to fabricate Co3O4/NiO nanocomposites derived from a bimetallic MOF, with a keen focus on harnessing their potential for electrochemical energy storage uses. Electrochemical analysis of the Co3O4/NiO nanocomposite reveals an exceptional capacitance of up to 180.4F/g at 0.2 A/g, demonstrating exceptional performance and robust stability over a notable 1200 cycles. Furthermore, the Co3O4/NiO nanocomposite exhibits remarkable electrocatalytic performance, achieving a utmost current density of 135.6 mA/cm2 at 0.6 V along with excellent long-term electrochemical stability. This remarkable capacitance and oxidation of methanol underscores the suitability of these nanocomposites for advanced electrochemical energy storage and fuel cell uses, emphasizing their potential for enriched performance in such systems.

A novel arrangement of active and ultra-stable electrocatalyst based on iron/nickel/cobalt oxy/hydroxides for continuous oxygen evolution from alkaline seawater splitting

This research offers novel ideas for development a new class of materials with enhanced OER kinetics utilizing an easy electrochemical deposition technique. Here, the Ti/CoNiyOx/FeOOH electrocatalyst was prepared in two steps. First, CoNiyOx thin film was anodically electrodeposited on an activated titanium substrate. Then iron oxyhydroxide (FeOOH) nanosheets were cathodically electrodeposited on the first layer. The properties of this electrocatalyst was evaluated and compared with some monolayer electrocatalysts using field emission scanning electron microscopy (FE-SEM), Raman, energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical methods. The Ti/CoNiyOx/FeOOH electrode requires an overpotential less than 330 mV at 100 mA/cm2 with Tafel constant of only 23.7 mV/dec for OER. The Ti/CoNiyOx/FeOOH electrode delivered long-term electrochemical stability in a solution containing corrosive chloride ions for more than 90 h at a constant current density of 100 mA/cm2 (with less than 9 % potential increase). Overall seawater splitting using the synthesized Ti/CoNiyOx/FeOOH electrode was performed at a current density of 100 mA/cm2 by a voltage as low as 1.58 V. The exceptional activity was ascribed to the synergistic effects of high electrochemical active sites and appropriate charge transfer ability found in CoNiyOx/FeOOH junction.

α-Mn2O3 porous fibers synthesized by air-heated solution blow spinning (A-HSBS) technique: electrochemical assessment for oxygen evolution reaction in alkaline medium

In this work, we report a novel synthesis route of α-Mn2O3 porous fibers obtained by air-heated solution blow spinning (A-HSBS) and their application as an electrocatalyst for the oxygen evolution reaction (OER). Our α-Mn2O3 porous fibers presented superior OER performance to other electrocatalysts reported in the literature, and it is because the fibrous morphology and multiple Mn charge states, which lead to a small overpotential of 378 mV @ 10 mA cm−2. Furthermore, the fibrous α-Mn2O3 electrode exhibited long-term electrochemical stability confirmed by chronopotentiometry testing for 18 h at a current density of 10 mA cm−2 and showing retention/preservation of microstructural properties. Our results underscore the potential of the A-HSBS for producing electrodes with a fiber-like morphology, based on transition metals. The proposed synthesis route can provide economical, durable, and efficient electrocatalysts for water splitting, which can be applied in several applications, such as electrocatalysts, biosensors, among others.

MnO@Mn2O3 nanocrystals embedded in biochar networks for sustainable anode of lithium-ion batteries

MnO is an alternative for commercial graphite as anode material for lithium-ion batteries (LIBs), if the issue of unstable performance caused by volume changes, poor conductivity, and changes in valence state of Mn is addressed. In this study, a series of nano MnO/biochar-containing composite materials were prepared with Mn(NO3)2, urea and pomelo peel as raw materials, via simple hydrothermal treatment and calcination, as anode materials for LIBs, where the biochar was used as inexpensive conductive medium and volume buffer. The electrochemical performance of the composite materials shows complicated correlation with the biochar contents, which associate with different carbonization temperatures. Elaborate characterizations with XRD, SEM, TEM, and Mn 2p, Mn 3s XPS spectra were conducted and jointly analyzed, which revealed that the surface of MnO nanocrystals undergoes different degrees of oxidation. The thickness of the surface amorphous Mn2O3 layer on the MnO nanocrystals influences the long-term electrochemical stability more significantly than the circumstances of biochar encapsulation, which was proved through cyclic voltammetry (CV) measurements. A composite material with moderate biochar content and thin layer of Mn2O3 coating on MnO nanocrystals will show more stable electrochemical performance. Based on this principle, one regulated composite material (MnOx/BC-650) gives an ultra-stable capacity of 446.9 mAh∙g−1 at 500 mA∙g−1 after 200 cycles. This study provides new insight for both revealing the true structure of manganese oxides and developing long-term stable MnO-containing anode materials for LIBs.

A Study of the Long-Term Electrochemical Stability of Thin-Film Titanium-Platinum Microelectrodes and Their Comparison to Classic, Wire-Based Platinum Microelectrodes in Selected Inorganic Electrolytes.

This paper discusses the electrochemical properties of thin-film, planar, titanium-platinum (Ti-Pt) microelectrodes fabricated using glass or silicon substrates and compares their performance to the classic platinum (Pt) microelectrodes embedded in glass. To analyze the possible differences coming both from the size of the tested electrodes as well as from the substrate, short- and long-term electrochemical tests were performed on selected water electrolytes (KCl, HCl, KOH). To study the electrochemical response of the electrodes, the cyclic voltammetry (CV) measurements were carried out at different scanning rates (from 5 to 200 mV/s). Long-term tests were also conducted, including one thousand cycles with a 100 mV/s scan rate to investigate the stability of the tested electrodes. Before and after electrochemical measurements, the film morphology was analyzed using a scanning electron microscope (SEM). The good quality of the thin-film Pt electrodes and the high repeatability in electrochemical response have been shown. There are minor differences in standard deviation values taken from electrochemical measurements, comparing thin-film and wire-based electrodes. Damages or any changes on the electrodes' surfaces were revealed by SEM observations after long-term electrochemical tests.

Controlled crystallinity of LiTaO3 surface layer for single-crystalline Ni-rich cathodes for lithium-ion batteries and all-solid-state batteries

Various functional materials have been explored as surface-coating layers for Ni-rich cathode materials used in lithium-ion batteries (LIBs) aiming to enhance their long-term cycling performance and electrochemical stability under high-voltage operation. In particular, lithium tantalate (LiTaO3) has received considerable attention as a promising candidate due to its distinct physicochemical properties, including high ionic conductivity, wide voltage window, low band-gap energy, and excellent mechanical strength. These characteristics are beneficial for effective surface stabilization of Ni-rich cathode materials, which currently suffer from poor cycling performance, mainly due to issues related to structural instability with elevated Ni concentrations. In this respect, we report the benefits of surface coating with LiTaO3 on the electrochemical properties of single-crystalline Ni-rich cathode materials (SNCM) for successful implementation in high-energy LIBs. The controlled crystallinity of the LiTaO3 surface layer directly affects the reversibility as well as interfacial stability of the SNCM cathode under various operating conditions. The tailored crystallinity of LiTaO3 surface layer is mainly responsible for enhancing the cycle performance of SNCM cathodes under high-temperature (60 °C) and high-voltage (4.5 V vs. Li/Li+) operations. Our findings will significantly contribute to the development of robust and reliable cathode materials for high-energy LIBs.

Engineered oxidation states in NiCo2O4@CeO2 nanourchin architectures with abundant oxygen vacancies for enhanced oxygen evolution reaction performance

Sluggish oxygen evolution reaction (OER) as the half reaction of water electrolysis hindered the production of clean hydrogen, necessitates a cost-effective electrocatalyst. Spinel nickel cobaltite (NiCo2O4), characterized by its lower cost, flexibility in oxidation states of cations, and stable spinel structure, holds promise as an OER electrocatalyst. However, there is still room for improvement in terms of its intrinsic electrochemical activity, conductivity, and active surface area. Inspired by the flexible valence states of Ni and Co, in this study, CeO2 was introduced into NiCo2O4 for further electronic structure adjustment. The result was the synthesis of an urchin-like NiCo2O4@CeO2 (NCOC), and the elucidation of its formation mechanisms, expressed conclusively through reaction formulas. NCOC, characterized by an open architecture and a rough surface, ensures rapid mass transportation and charge diffusion. Within NCOC, numerous oxophilic Ce3+ sites with oxygen vacancies construct electron transport pathways, accelerating charge-transfer. This simultaneously induces an increase in the oxidation states and proportions of Ni3+ and Co3+ in NCOC, reinforcing the covalence of Ni–O and Co–O bonds, expediting the ad/desorption of intermediates during OER. The electronic structure variations of NCOC were further verified through density functional theory (DFT) analyses, revealing alterations in adsorption configurations of intermediates and a decrease in adsorption free energies for intermediates on NCOC during OER. In practical terms, NCOC demonstrated a low overpotential of 228 mV at a current density of 10 mA cm−2 under 1 M KOH, maintaining long-term electrochemical stability for 100 h. Overall, this study provides a universal approach for designing highly cost-efficient electrocatalysts for OER.

An electrochemical catalyst of CUST-581 for methanol oxidation and hydrogen peroxide detection

A new Ni-MOF(CUST-581), [(Ni)2(BIMB)1.5(BTB)] [CUST-581, H3BTB = 1,3,5-tris(4-carboxyphenyl)benzene, BIMB = 1,4-bis((1H-imidazolyl)methyl)benzene], was synthesized using the solvothermal method. CUST-581 exhibited not only high current density but also long-term electrochemical stability during the measurement of methanol oxidation reactions. Moreover, CUST-581 was used as an enzyme-free electrochemical sensing platform for the determination of H2O2. The electrochemical sensing performance of the CUST-581 modified glassy carbon electrode for H2O2 was evaluated by cyclic voltammogram and time measurements in alkaline solutions. The sensor showed a good linear range (20 μM-5000 μM), a low detection limit of 0.28 μM, high sensitivity (0.37 mA mM−1 cm−2) and fast response. Importantly, good reproducibility and repeatability, long time stability and excellent selectivity were obtained in the fabricated H2O2 sensor. The results of the actual samples suggest that the Ni-MOF/GCE sensor could be a promising candidate for H2O2 sensing applications.

Solvation Structure Regulation for Highly Reversible Aqueous Al Metal Batteries.

Metallic Al has been deemed an ideal electrode material for aqueous batteries by virtue of its abundance and high theoretical capacity (8056 mAh cm-3). However, the development of aqueous Al metal batteries has been hindered by several side reactions, including water decomposition, Al corrosion, and passivation, which arise from the solvation reaction of Al and H2O in conventional aqueous electrolytes. In this work, we report that water activity in electrolyte can be suppressed by optimizing the Al3+ solvation structure through intercalation of polar pyridine-3-carboxylic acid in an aluminum trifluoromethanesulfonate aqueous environment. Furthermore, the pyridine-3-carboxylic acid molecules are inclined to alter the surface energy of Al, thus suppressing the random deposition of Al. As a result, the Al corrosion in the hybrid electrolyte is restrained, and the long-term electrochemical stability of the electrolyte is tremendously improved. These merits bring remarkable reversibility to aqueous Al batteries using Al-preintercalated MnO2 cathodes, delivering a retaining energy density of >250 Wh kg-1 at 0.2 A g-1 after 600 cycles.

Analyzing the Effect of Nano-Sized Conductive Additive Content on Cathode Electrode Performance in Sulfide All-Solid-State Lithium-Ion Batteries

All-solid-state lithium-ion batteries (ASSLBs) have recently received significant attention due to their exceptional energy/power densities, inherent safety, and long-term electrochemical stability. However, to achieve energy- and power-dense ASSLBs, the cathode composite electrodes require optimum ionic and electrical pathways and hence the development of electrode designs that facilitate such requirements is necessary. Among the various available conductive materials, carbon black (CB) is typically considered as a suitable carbon additive for enhancing electrode conductivity due to its affordable price and electrical-network-enhancing properties. In this study, we examined the effect of different weight percentages (wt%) of nano-sized CB as a conductive additive within a cathode composite made up of Ni-rich cathode material (LiNi0.8Co0.1Mn0.1O2) and solid electrolyte (Li6PS5Cl). Composites including 3 wt%, 5 wt%, and 7 wt% CB were produced, achieving capacity retentions of 66.1%, 65.4%, and 44.6% over 50 cycles at 0.5 C. Despite an increase in electrical conductivity of the 7 wt% CB sample, a significantly lower capacity retention was observed. This was attributed to the increased resistance at the solid electrolyte/cathode material interface, resulting from the presence of excessive CB. This study confirms that an excessive amount of nano-sized conductive material can affect the interfacial resistance between the solid electrolyte and the cathode active material, which is ultimately more important to the electrochemical performance than the electrical pathways.

Engineering Oxygen Vacancies in (FeCrCoMnZn)3O4-δ High Entropy Spinel Oxides Through Altering Fabrication Atmosphere for High-Performance Rechargeable Zinc-Air Batteries.

High entropy oxides (HEOs) offer great potential as catalysts for oxygen electrocatalytic reactions in alkaline environments. Herein, a novel synthesis approach to prepare (FeCrCoMnZn)3O4-δ high entropy spinel oxide in a vacuum atmosphere, with the primary objective of introducing oxygen vacancies into the crystal structure, is presented. As compared to the air-synthesized counterpart, the (FeCrCoMnZn)3O4-δ with abundant oxygen vacancies demonstrates a low (better) bifunctional (BI) index of 0.89V in alkaline media, indicating enhanced electrocatalytic oxygen catalytic activity. Importantly, (FeCrCoMnZn)3O4-δ demonstrates outstanding long-term electrochemical and structural stability. When utilized as electrocatalysts in the air cathode of Zn-air batteries, the vacuum atmosphere synthesized (FeCrCoMnZn)3O4-δ catalysts outperform the samples treated in an air atmosphere, displaying superior peak power density, specific capacity, and cycling stability. These findings provide compelling evidence that manipulating the synthesis atmosphere of multi-component oxides can serve as a novel approach to tailor their electrochemical performance.

Constructing Stable MoOx-NiSx Film via Electrodeposition and Hydrothermal Method for Water Splitting

The hydrothermal method is a frequently used approach for synthesizing HER electrocatalysts. However, a weak tolerance to high temperature is an intrinsic property of carbon cloth (CC) in most situations, and CC-based catalysts, which require complex technological processes in low-temperature environments, exhibit weak stability and electrochemical performance. Hence, we provide a new solution for these issues. In this work, MoO3-NiSx films of 9H5E-CC catalysts are synthesized, first through electrodeposition to form Ni particles on CC and then through a hydrothermal reaction to reform the reaction. The advantages of this synthetic process include mild reaction conditions and convenient operation. The obtained MoO3-NiSx film presents excellent catalytic activity and stability for HER. MoO3-NiSx film requires only a low overpotential of 142 mV to drive 10 mA cm−2 for HER in 1.0 m KOH, and the obtained 9H5E-CF film only needs 294 mV to achieve 50 mA cm−2 for OER. Remarkably, they also show excellent OER, HER, and full water splitting long-term electrochemical stability, maintaining their performance for at least 72 h. This work can be expanded to provide a new strategy for the fabrication of stable, high-performing electrodes using simple, mild reaction conditions.

Hybrids Composed of an Fe-Containing Wells–Dawson Polyoxometalate and Carbon Nanomaterials as Promising Electrocatalysts for the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is a key cathodic reaction in energy-converting systems, such as fuel cells (FCs). Thus, it is of utmost importance to develop cost-effective and efficient electrocatalysts (ECs) without noble metals to substitute the Pt-based ones. This study focuses on polyoxometalate (POM)-based ECs for ORR applications. A Wells–Dawson POM salt K7 [P2W17(FeOH2)O61].·20H2O was immobilised onto graphene flakes and multiwalled carbon nanotubes doped with nitrogen, denominated as P2W17Fe@GF_N8 and P2W17Fe@MWCNT_N8. The successful preparation of the composites was proved with various characterisation techniques, including FTIR, XPS and SEM. Both materials showed good ORR performance in an alkaline medium with similar potential onset values of ~0.84 V vs. RHE and diffusion-limiting current densities of −3.9 and −3.3 mA cm−2 for P2W17Fe@MWCNT_N8 and P2W17Fe@GF_N8, respectively. Furthermore, both composites presented low Tafel slopes (48–58 mV dec−1). Chronoamperometric tests revealed that the as-prepared nanocomposites rendered a significant improvement achieving between 90 and 94% of current retention in tolerance to methanol in comparison with Pt/C, and moderate to good long-term electrochemical stability with current retentions comprised between 68 and 88%. This work reinforces the use of POMs as important electroactive species for the preparation of alternative ORR electrocatalysts, exhibiting good activity, stability and selectivity towards the ORR in the presence of methanol.