In the search for materials used as active species in cathodes for K-ion batteries, only a few compositions of transition metal oxides or transition metal polyanionic frameworks have been proposed so far. In this work, we report for the first time the synthesis and study of the electrochemical activity an original K3MnO4 polymorph. This phase is a 0D-type structure made of isolated MnO4 tetrahedra surrounded by K+ ions. A reversible charge capacity of almost one K+ per unit formula at the average voltage of 2.3 V vs K+/K is obtained, leading to the reversible formation of K2MnO4 through a biphasic process.

By optimizing the ligands, the structure of a coordination polymer can be adjusted to realize the regulation and optimization of the properties of the coordination polymer materials. Coordination polymers not only exhibit a variety of molecular topologies but also have good application prospects in adsorption, separation, catalysis, photoelectric magnetism, and so on. Recently, coordination polymers are being well used in precursors for electrocatalysts because of their high surface area and porous structure. Therefore, we selected two ligands with a similar structure in which the two coordination groups were located at the paracene and intersite of the benzene ring, that is, 4-(1H-1,2,4-triazol-1-yl) benzoic acid (Hbza) and 3-(1H-1,2,4-triazol-1-yl) benzoic acid (3-Hbza). We found that there are obvious differences in the crystal structure between Zn-bza and Zn-3bza, which is due to the different relative position between the carboxyl group and the triazole group leading to the formation of different interactions, so we further studied the performance of their derived materials and found that the derivative materials of the coordination polymer formed by 3-Hbza have a better electrocatalytic performance. This paper provides a strong support for the idea that a slight change in the structure of the ligand will affect the final structure and thus the final performance.

Sodium-ion batteries (SIBs) with high energy density, improved safety, and low cost are exciting candidates for next-generation energy storage and electrical vehicles. Cathode materials are the core component for SIBs. Recently, an experimental study reported a promising Na2FeS2 cathode with a specific structure consisting of edge-shared and chained FeS4 tetrahedra as the host structure and a high capacity of 320 mA h g–1 for sodium storage. However, the underlying reaction mechanisms and Na migration pathways have not been fully understood. In this study, density functional theory (DFT) and DFT + U calculations are performed to study the structural stability, phase stability, electronic properties (spin polarization density of states), average voltage using total energy based on fully charged and discharged states, and Na-ion transport and diffusion channel using ab initio molecular dynamic simulations of the NaXFeS2 (X = 2, 1.5, and 1) cathode materials. It is revealed that Na2FeS2 is unstable at 0 K and possesses a theoretical capacity of 323 mA h g–1 with a low diffusion barrier of 0.40 eV in NaxFeS2 series. Moreover, some transition metals are substituted at Fe sites to evaluate the structural effect of Na2FeS2, in which Na2MnS2 exhibits excellent structural stability, low hull energy, and high theoretical capacity of 325 mA h g–1, which could be appealing for researchers in the future.

High interfacial compatibility between electrolytes and electrodes is of great importance for the stable operation of all-solid-state batteries (ASSBs). Here, we report that the introduction of LiBH4 into Li2B12H12-5Li2B10H10 improves the electrochemical window to ∼3.0 V and Li-ion conductivity to 1.0 × 10–4 S cm–1 at room temperature (RT). Moreover, the Li2B12H12-5Li2B10H10-6LiBH4 electrolyte exhibits good compatibility with a metallic Li anode and TiS2 cathode, allowing the stable operation of the all-solid-state In1.3Li0.3||TiS2 cell for 120 cycles at 0.1 C and RT, with 117.8 mAh g–1 of capacity and ∼100% of the coulombic efficiency. This work illustrates that a hydroborate electrolyte with high ionic conductivity and large electrochemical stability can enable the development of an ASSB with a voltage up to 2.7 V.

Harvesting the vibration energy commonly found in engines, air compressors, and other machines is of great significance for energy recovery and reutilization. However, due to the small vibration amplitude and non-single vibration directions, the conventional vibration energy harvesters based on triboelectric nanogenerators (TENGs) have a low efficiency. In this work, we proposed a TENG with a rotational freestanding mode (RFM-TENG), which can effectively harvest the mechanical vibration energy with a small amplitude, high frequency, and multiple directions. The working principle and performance characteristics of each TENG unit were demonstrated through theoretical analysis and electrical simulations. To further improve the harvest efficiency, we prepared a room-temperature vulcanized silicone rubber (RTV) film doped with high dielectric constant halloysite nanotubes powder as the triboelectric layer, which increased the open-circuit voltage by 100% and the short-circuit current by 85% at an optimal doping ratio of 7 wt %. When the RFM-TENG was installed on an air compressor, it generated an open-circuit voltage of about 60 V and a maximum output power of 45 μW and allowed 30 commercial LEDs to light up simultaneously. RFM-TENG has the advantages of strong nonlinearity, high sensitivity, and multi-directional response and has potential applications in the field of smart factory and digital twin.

Protonic ceramic electrochemical cells (PCECs) represent promising technologies in the production of clean electricity, decarbonized hydrogen, chemicals, and fuels at intermediate temperatures. One of the challenges in commercializing PCECs is to produce the electrolyte materials on a large scale. The conventional solid-state reaction (SSR) method suffers from tedious synthesis procedures and low phase purity of the products due to the formation of unwanted secondary phases. Herein, we report an improved SSR (i-SSR) method for kilogram-scale production of high phase-purity electrolyte material BaZr0.4Ce0.4Y0.1Yb0.1O3−δ (BZCYYb4411). In this method, the ball-milled precursor powders are pelletized prior to calcination, which effectively reduces the length of the diffusion paths between the components during perovskite phase formation. The synthesis procedure and calcination temperature are carefully optimized for efficient and repeatable production based on the powder crystallization behavior. A combined technoeconomic analysis and life cycle assessment modeling suggest that the i-SSR method could reduce the total production cost and greenhouse gas emissions by up to 19% and 39%, respectively, compared to the conventional SSR method. The high quality of the synthesized electrolyte material is corroborated by the excellent electrical conductivity and electrochemical performance of the fabricated PCEC cells.

This study synthesizes the nickel–cobalt supported by the metal–organic framework CPO-27 (coordination polymer of Oslo, Ni–Co-CPO-27) and g-C3N4, showing outstanding catalytic activity and stability for oxygen reduction reaction in alkaline media, notated by NiCo2-CPO-27/PCN-HT (PCN-HT: heat-treated polymeric carbon nitrite). The half-wave potential of NiCo2-CPO-27/PCN-HT is 0.82 V, and the electron transfer number is around 3.99, which is close to the activity of Pt/C. The stability test of NiCo2-CPO-27/PCN-HT demonstrates only 0.01 V decade of the half-wave potential after 30,000 cycles. The synergistic effects of Ni–Co metals, pyridinic-N species, and graphitic-N species contribute to the outstanding performance of NiCo2-CPO-27/PCN-HT. The anion exchange membrane fuel cell (AEMFC) using NiCo2-CPO-27/PCN-HT in the cathode shows excellent performance with a maximum power density of 224.4 mW cm–2, 20% higher than AEMFC using the Pt/C under the same condition.

In this study, we present a pyrolytically derived iron-based nonprecious metal catalyst (NPMC), Fe3C embedded in heteroatom (S,N)-codoped carbon matrix, and explored it as a potential NPMC for oxygen reduction in alkaline media. The as-prepared catalysts are well characterized for their structure, crystallite size, morphology, different bonding states of the dopants, and defect levels in the carbon matrix. The optimization is performed for ideal reaction temperature and dopant amounts in Fe3C@C nanostructures. From the electrochemical study, it is found that among the different variants, the sample prepared at a temperature of 800 °C with 20 wt % dopant, i.e., Fe3C@C-SN/25-800, shows a more positive onset potential (Eonset) of 0.844 V (vs reversible hydrogen electrode (RHE)) and a low half-wave potential (E1/2) value of 0.670 V. It also shows good long-term oxygen reduction reaction (ORR) stability and methanol tolerance in a 0.1 M KOH aqueous electrolyte. The measurement of intrinsic parameters, double-layer capacitance (Cdl), and charge transfer resistance (RCT) values validate the current–voltage profile of the samples. The major active sites are identified as Fe–Nx and Nx–C in the nanostructures. Fe3C@C-SN/25-800 also exhibits considerable oxygen evolution reaction (OER) activity among its variants and requires a potential difference (ΔE = E1/2(ORR) – EJ=10 mA cm–2 (OER)) of 0.980 V for overall oxygen electrochemistry. The best electrocatalytic activity can be attributed to the combination of several factors, namely, chosen reaction temperature, dopant concentration, better graphitization, and the presence of a high amount of heteroatoms suitably aligned in the carbon matrix (pyridinic-N, thiophenic-S, etc.) that synergistically enhance the overall performance.

As photocatalysts, holey carbon nitride nanosheets (HCNS) have attracted considerable attention. Although many advances have been made in the preparation of HCNS, challenges remain in the low-cost preparation of HCNS. In this work, a one-step strategy for preparing HCNS was explored. First, melamine was placed in a small ceramic boat, which was in a large ceramic boat. Next, the gap between two ceramic boats was filled with copper oxide. Finally, the two boats were wrapped in tin foil and heat-treated. During the thermal polymerization of melamine, released ammonia is decomposed by copper oxide, and the equilibrium shifts to the right, further accelerating the release of ammonia and achieving the preparation of HCNS. Meanwhile, partial copper oxide is reduced to copper by ammonia. After a simple heat treatment, the copper in the mixture can be converted back to copper oxide and realize recycling. The obtained HCNS displays high looseness and enhanced photogenerated charge carrier separation efficiency. Our results indicate that the filled copper oxide can effectively decompose ammonia, affect the thermal condensation atmosphere, and significantly improve the photocatalytic activity of carbon nitride. This work provides a new idea for further fundamental and applied research of HCNS.

The development of catalytic technology for CO2 recycling attracts much international attention for producing valuable chemicals and reducing CO2 emissions. Photothermal dry reforming of methane (PT-DRM) is a promising technology to convert CO2 into syngas (a mixture of CO and H2) using solar energy. In this study, we found that silica-supported nickel catalysts (Ni/SiO2) prepared via Ni phyllosilicate by the ammonia evaporation methods exhibited improved catalytic activity and enhanced resistance to sintering and carbon deposition in PT-DRM under visible and near-infrared light compared to that prepared by the conventional wetness impregnation method due to the highly dispersed Ni nanoparticles coated with thin SiO2 layers. The catalytic activity and surface temperature reached maximums at the Ni loading of around 25 wt %. Furthermore, the light absorption and thermal diffusivity of the catalyst material increased with the increase in Ni loading, where the former contributes to the increase of the surface temperature and the latter to the decrease due to the higher heat dissipation. Hence, the Ni loading had positive and negative effects on the irradiated surface temperature of the catalytic part, and these thermal properties affected the photothermal catalytic activity for PT-DRM. These findings indicate the significance of suppressing heat dissipation in the design of photothermal catalysts for effective light energy utilization.

The incrementally rising efficiency of perovskite-based photovoltaic devices has established technology as a hot topic in past years. Transitioning this class of materials from laboratorial to commercial application is key to the future of clean energy generation. In the interest of this transition, scalable fabrication and reproducibility are challenges to be overcome. Additionally, being a highly dynamic field with fast-paced innovation, perovskite research lacks in structured comprehensive studies focusing on the processing parameters, especially when compared to commercial technologies, such as silicon-based devices. This study proposes a design of experiments (DoE) approach to analyze and optimize the fabrication of perovskite thin films by ultrasonic spray coating, a scalable technique. The investigation of deposition parameters one factor at a time (OFAT) and the more in-depth full factorial analysis of three key input variables allowed the assessment of the impact level of each factor on the quality and performance of the obtained films of the fabricated photovoltaic devices. Furthermore, the full factorial analysis reveals the presence of interactions between factors. The study revealed that a shorter distance between the air gun and the sample (2 cm) coupled with high gas pressure (7.6 bar) during the quenching step were the most influential parameters for the production of high-quality films, leading to an average efficiency of 14.8%.

SnO2 is considered as a promising electron transport material for carbon-based perovskite solar cells (C-PSCs) due to its excellent electron mobility, stability over TiO2, and low-temperature processing. However, the lattice mismatch and poor contact quality of the SnO2/CH3NH3PbI3 interface, as well as oxygen vacancies, usually lead to nonradiative recombination and limit the further improvement of photovoltaic performance. In this paper, two chitosan derivatives, chitosan quaternary ammonium salt (HACC) and carboxymethyl chitosan (CMCS), were used as additives for SnO2 to adjust the energy level and improve the contact performance of the SnO2/CH3NH3PbI3 interface. These two additives have suitable terminal active functional groups, amino group and hydroxyl group, which can interact with SnO2 and CH3NH3PbI3 at the interface, induce the crystal growth of the perovskite, and play a good role in passivating interfacial defects. Therefore, the interfacial contact and the charge-transfer ability were effectively enhanced. As a result, the addition of HACC and CMCS increased the PCE of C-PSCs from 10.17 to 12.42 and 13.39%, and the repeatability and long-term stability of the corresponding unencapsulated C-PSCs were also significantly improved. This work expands the vision for the future interface modification strategies to improve the device performance and is conducive to promote the further commercialization of C-PSCs.

Efficient charge extraction in lead halide perovskite nanocrystals is frequently sought-after and probed using various probe molecules. Often ignored, the chemical bonding of the molecules to the perovskite’s surface, as dictated by the terminal anchoring functional group, can have implications on the excited-state interactions between perovskite nanocrystals and the charge-shuttling molecules. Considering the remarkability of the recent work on ferrocene-based molecules in allowing charge transfer in perovskite nanocrystals, we have employed ferrocene molecule functionalized with various functional groups to understand the binding and charge-transfer process at the interface of the perovskite nanocrystal and the redox relay molecule. We evidenced that the charge transfer enhanced with enhancement in binding, as validated by the association constant evaluated as high as 1.71 × 107 M–1. In particular, the −COOH and −NMe2 functional groups led to the efficient quenching of photoluminescence (PL) emission and a decrease in photoluminescence lifetime than the other functional group analogues, showing their feasibility in charge transfer studies. More importantly, the −NMe2 functional group indicated passivation of the defects on the perovskite surface, attributed to the interaction between the lone pair of nitrogen and the undercoordinated surface Pb2+ cations. This was also evident in the transient absorption spectra, where the excited-state interaction could be analyzed better. This work opens avenues for exploring anchoring moieties in facilitating charge transfer across the perovskite interface, thus impacting its photocatalytic applications.

Photoelectrochemical solar water splitting has become a potential approach for producing clean hydrogen fuels by utilizing semiconductor photoelectrodes and solar energy. Among emerging metal oxide photoelectrodes, iron vanadate (FeVO4) with its unique electronic band structure and suitable bandgap energies for absorbing visible light from the solar spectrum has become a promising photoanode. However, the reported photocurrent density of this material is still low because of the poor water oxidation kinetics and the slow separation of carriers, leading to recombination at the surface. In this study, we attempted to solve these limitations by nanostructuring the FeVO4 photoanode and modifying its surface with cocatalysts (CoOx, CoPi, and CoOx–CoPi). Both photocurrent and onset potential are significantly improved, resulting from the enhancement of charge injection and separation efficiencies. For the first time, the dual layer of oxygen evolution CoOx–CoPi catalysts is found more effective than single-layer CoOx or CoPi catalysts for the nanoporous FeVO4 photoanode with the increased photocurrent density at 1.23 V vs RHE of a 5-fold improvement compared to the pristine FeVO4. This result offers a strategy to further improve FeVO4 photoanode performance for efficient solar water splitting toward practical applications.

Organic electrodes have been identified as promising energy-storage materials for aqueous zinc-ion batteries (AZIBs). Small molecular materials have ideal redox properties, high specific capacity, and structural diversity, making them a category of cathode candidates for AZIBs. However, the instability and dissolution during the extraction and insertion of H+/Zn2+ limit their application of the long-cycle stability for AZIBs. Herein, a small-molecule nanosheet (NI-DAQ, ∼14 nm in thickness) with imide linkage is designed and synthesized by the condensation of anthraquinones and anhydrides. It not only inhibits the dissolution of monomer electrodes but also boosts the reactivity and conductivity of the whole molecule by the introduction of π-conjugated imide groups and extended aromatic planes. Therefore, the NI-DAQ electrode obtains a large initial capacity of 191.9 mA h g–1 at 50 mA g–1 and superior cyclability after 3000 cycles at 500 mA g–1 with a minor average capacity fading rate of 0.01% per cycle. Moreover, in situ Fourier transform infrared (FT-IR) and ex situ X-ray photoelectron spectroscopy (XPS) characterization techniques have been implemented to investigate the redox mechanism of C═O units in AZIBs for the NI-DAQ electrode. Thus, a promising conductive molecule is developed and explored in this paper, which can provide insights into the application of organic materials in AZIBs.

The sluggish kinetics of electrocatalysts in the alkaline hydrogen evolution reaction (HER) is a critical challenge to attain efficient progress in water electrolysis for carbon-neutral hydrogen production. Here, we present a high-performance and durable heterostructure of NiMo/CoMoO4 for the alkaline HER constructed via a two-pot in situ growth strategy on a nickel foam (NF). The density of active sites and the surface area of the hybrid catalyst augmented almost three-fold compared to those of pristine CoMoO4. The heterostructure composed of metallic NiMo and oxygen vacancy (Ov)-confined CoMoO4 facilitated the H adsorption on the metallic side and OH adsorption on the oxide side. The hierarchical hybrid catalyst on NF featured a low overpotential of 102 mV at 10 mA cm–2, approaching that of platinum on carbon (83 mV) in 1.0 M KOH. The turnover frequency of 0.012 s–1 at the overpotential of 100 mV of NiMo/CoMoO4 is six times higher than that of CoMoO4, 0.002 s–1. In addition, the fabricated heterostructure is a highly durable HER catalyst at 30 mA cm–2 for 30 h. The Faradaic efficiency recorded by a gas chromatograph at 10 and 100 mA cm–2 revealed nearly 100 and 86–95% hydrogen production efficiency, respectively.

Better understanding of the oxygen evolution reaction on cobalt oxides requires insights into the oxide–solution interface structure and composition under reaction conditions. We here present operando studies of electrodeposited epitaxial thin films with planar surface morphology that couple X-ray absorption spectroscopy, surface X-ray diffraction, and electrochemical measurements. This enabled us to disentangle bulk and surface contributions of the XAS signal and to correlate the cobalt oxidation state with the surface structure of cobalt oxide films. In the case of Co3O4(111) films, we show a one-to-one correlation between the Co oxidation state increase in the pre-OER potential range and the potential-dependent thickness of the reversibly formed amorphous layer on the oxide surface. From this correlation, we conclude that this amorphous layer is exclusively composed of Co3+. In the case of CoOOH(001) films, we show that no such surface amorphization takes place and that the small oxidation state change with potential may be attributed to the progressive deprotonation of the surface Co-OH groups. For both oxides, the amount of Co4+ remains below the detection limit.

Solid-state batteries can be built based on thiophosphate electrolytes such as β-Li3PS4. For the preparation of these solid electrolytes, various solvent-based routes have been reported. For recycling of end-of-life solid-state batteries based on such thiophosphates, we consider the development of dissolution and recrystallization strategies for the recovery of the model compound β-Li3PS4. We show that recrystallization can only be performed in polar, slightly protic solvents such as N-methylformamide (NMF). The recrystallization is comprehensively studied, showing that it proceeds via an intermediate phase with composition Li3PS4·2NMF, which is structurally characterized. This phase has a high resistivity for the transport of lithium ions and must be removed in order to obtain a recrystallized product with a conductivity similar to the pristine material. Moreover, the recrystallization from solution results in an increase of the amorphous phase fraction next to crystalline β-Li3PS4.

La0.6Sr0.4CoO3−δ (LSC) perovskite, as a potential catalyst precursor for hydrogen (H2)-rich production by steam reforming of methanol (SRM) and oxidative steam reforming of methanol (OSRM), was investigated. For this purpose, LSC was synthesized by the citrate sol–gel method and characterized by complementary analytical techniques. The catalytic activity was studied for the as-prepared and prereduced LSC and compared with the undoped LaCoO3−δ (LCO) at several feed gas compositions. Furthermore, the degradation and regeneration of LSC under repeated redox cycles were studied. The results evidenced that the increase in the water/methanol ratio under SRM, and the O2 addition under OSRM, increased the CO2 formation and decreased both the H2 selectivity and catalyst deactivation caused by carbon deposition. Methanol conversion of the prereduced LSC was significantly enhanced at a lower temperature than that of as-prepared LSC and undoped LCO. This was attributed to the performance of metallic cobalt nanoparticles highly dispersed under reducing atmospheres. The reoxidation program in repetitive redox cycles played a crucial role in the regeneration of catalysts, which could be regenerated to the initial perovskite structure under a specific thermal treatment, minimizing the degradation of the catalytic activity and surface.

Employing a non-noble trimetal oxide system toward an electrochemical nitrogen reduction reaction (eNRR) instead of a century-long and CO2-emission Haber–Bosch process reveals a green path for NH3 production. In this work, the trimetal Fe–Mn–Ga oxide electrocatalyst was prepared with a facile one-pot hydrothermal method followed by annealing. Crystal structure, morphology, composition, and electrochemical properties were characterized. The flower-like (Fe,Mn,Ga)3O4–x spinel/tabular crystal-like (Mn,Fe)2O3–y bixbyite composite electrocatalyst was in situ formed with many active oxygen atoms on the oxygen vacancy sites and transition metals of Fe and Mn at multiple oxidation states. In a N2-saturated 0.1 M Na2SO4 solution, the NH3 yield rate at a potential of −0.6 V vs RHE is 814 μg h–1mgcat–1 (2036 μg h–1cm–2) with Faradaic efficiency (FE) of 5.77%, while the highest FE of 19.7% is achieved at −0.5 V with a yield rate of 599 μg h–1mgcat–1. The reaction mechanism for NH3 production is investigated and explained.