Hydrogen (H2) energy is presumed to be the most promising alternative to replacing traditional fossil fuels to achieve the global mission of carbon neutrality. Electrocatalytic water splitting driven by green electricity has been regarded as an ideal method for large-scale green hydrogen production with a minimal CO2 footprint. However, most of the reported electrocatalysts still suffer from large overpotentials and severe activity degradation at high current density (>1000 mA cm−2). Therefore, a comprehensive review to summarize the representative alkaline hydrogen evolution reaction (HER) electrocatalysts with large current densities is essential to guide the fabrication of promising industrial electrocatalysts. In this review, starting from the fundamental of water electrolysis, the design principles to acquire alkaline electrocatalysts with large current density and high stability are elaborated. The critical factors for achieving high-performance electrocatalysts to meet industrial H2 production are proposed. Additionally, the key processes for preparing self-supported electrodes are clarified. Afterward, the recently advanced self-supported transition metal-based electrocatalysts with high current density for alkaline HER are systematically summarized. Finally, personal perspective on future opportunities and challenges is highlighted. It is hoped this review can guide the rational design of self-supported high-current density electrocatalysts for future commercial H2 production.

Lithium–sulfur batteries (LSBs) that utilize sulfur and lithium (Li) metal as electrode materials are highly attractive for transportation applications due to their high theoretical gravimetric energy density. However, two major challenges currently impede the commercialization of LSB, which are the formation of Li dendrites and polysulfide shuttling. To mitigate these two effects, a protective film or artificial solid–electrolyte interface (SEI) can be applied directly to the Li-metal surface. Herein, the preparation of freestanding polyethylene oxide (PEO)-based films using tape casting as a scalable coating technique is presented. Moreover, the films are applied directly to the Li surface via a solvent-free method. To demonstrate the suitability of the developed PEO-based films, the long-term cycling performance of the lithium–sulfur cells is discussed. It is shown that the cells with the Li-metal surface protected by PEO-based films achieve better stability and reproducibility, reaching ≈400 mA h g S−1 after 250 cycles compared to ≈200 mA h g S−1 after 250 cycles for the bare Li-metal electrode. An extensive postmortem analysis of the Li-metal electrode surface with scanning electron microscopy is additionally shown, revealing that the PEO-based artificial SEIs form uniformly with a low level of defect layers at the interface with the Li-metal electrode, which indicates the creation of a stable SEI.

Herein, the thermoelectric characteristics of polytriarylamine-Lewis acid complex films were investigated by employing a horizontal device structure. Poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (PolyTPD) is doped with tris(pentafluorophenyl)borane (BCF) via Lewis acid–base reactions by varying the BCF molar ratio (0–300 mol%). The resulting PolyTPD:BCF films are spun on glass substrates and silver electrodes are deposited leading to the horizontal type of organic thermoelectric devices (OTEDs). The OTEDs with the PolyTPD:BCF films are examined by varying temperature differences up to 45 K between two silver electrodes directly contacting hot/cold sources. Both device current and voltage are proportionally increased with the temperature difference, leading to higher powers at larger temperature differences, irrespective of BCF molar ratio. However, the highest current is achieved at 50 mol% owing to the highest electrical conductivity, even though the device voltage is slightly lower at 50 than 20 mol%. The origin of high electrical conductivity is assigned to the formation of radical cations in PolyTPD chains by BCF doping, which is influenced by the reaction time. The device current can be also generated by the illumination of IR radiation (noncontact mode) that is away from the OTEDs with the PolyTPD:BCF films.

Dear Readers, It has been another great year for Advanced Energy and Sustainability Research. In early 2022 we were pleased to learn that the journal was accepted into the Emerging Sources Citation Index (ESCI) from Clarivate, and that the whole publication record dating back to 2020 would be added to the Web of Science. This is still an important step for a young journal, because it greatly increases the visibility of its published papers. Also, many institutions demand scientific manuscripts to be submitted to indexed journals only, so indexing can help to attract submissions. Later in 2022, Clarivate announced that all journals listed in the ESCI in a given year will automatically receive an Impact Factor in the following year, without the additional evaluation step they previously required. As you will know, it is an average of the citations in a given year for all relevant articles published in the two previous years. It therefore has some meaning on a journal level, but it does not reflect the usage and impact of an individual article. To better measure individual article performance, new metrics have been developed to reflect how articles are used and shared across different media, e.g., via tweets and so on. The move away from the Impact Factor as the sole metric for the evaluation of scientific research output is also a strong motivator behind the Declaration on Research Assessment (DORA). Wiley became a signatory of DORA in 2022, which means that we are emphasizing the Impact Factor less in our communications and working to broaden out to other article-level metrics. Of course, we know that the Impact Factor is still important to many authors, and we continue to monitor these developments.

In thin-film photovoltaics, such as organic and perovskite solar cells, charge extraction selectivity is crucial. In order to improve selectivity, charge transporting layers (doped and undoped) are frequently used; however, it is not well understood how a charge transporting layer should be designed in order to ensure efficient extraction of majority carriers while blocking minority carriers. This study clarifies how well charge transporting layers with varying majority carrier conductivities block minority carriers. The charge extraction by a linearly increasing voltage technique is used to determine the surface recombination velocity of minority carriers in model system devices with varying majority carrier conductivity in the transporting layer. The results show that transporting layers with high conductivity for majority carriers do not block minority carriers—at least not at operating voltages close to or above the built-in voltage, due to direct bimolecular recombination across the transporting layer–absorber layer interface. Design principles are furthermore discussed and proposed to achieve selective charge extraction in thin-film solar cells using charge transporting layers.

TiO2–based photocatalysis system for splitting water into hydrogen offers a sustainable and green technology to produce clean hydrogen energy. However, pristine TiO2 still exists inherent shortcomings restricting its practical applications. Herein, the impact of postprocessing approaches of protonic titanate on engineering of oxygen vacancy and photocatalytic hydrogen evolution of TiO2−x is studied. Subsequently, interfacial cocatalysts are successfully involved in the optimized TiO2−x for enhanced photocatalytic hydrogen evolution. TiO2−x with the highest photocatalytic hydrogen evolution performance of 3112.09 μmol g−1 h−1, denoted as TiO2–C, is selected to adjust the interface with Cu and MoS2 respectively. Cu–TiO2–C and MoS2–TiO2–C composites are synthesized to enhance the separation ability of photogenerated electron-hole pairs and significantly improve the photocatalytic hydrogen evolution performance. The photocatalytic hydrogen evolution rates of 5 wt% Cu–TiO2–C and 40 wt% MoS2–TiO2–C are 9225.75 and 5765.48 μmol g−1 h−1, respectively. It is proved that different postprocessing methods can tune the content of oxygen vacancy in TiO2−x and regulate the photocatalytic hydrogen evolution performance of TiO2−x materials. The interface regulation of the cocatalyst also contributes to the separation of photogenerated electron-hole pairs and serves as active sites to enhance hydrogen evolution performance.

All-solid-state lithium-sulfur (ASS-Li/S) batteries have recently attracted considerable attention owing to their high energy density and safety. To produce the cathode of an ASS-Li/S battery, sulfur (the cathode active material) must be combined with a conductive additive (electron conductor) because of the electronic insulating property of sulfur. Therefore, a compositing process of sulfur and conductive additives is necessary to produce ASS-Li/S batteries. However, existing compositing methods are neither scalable nor productive. Herein, for the first time, a hot-melt kneading process, as a scalable and productive compositing process, to produce composite particles of sulfur and a conductive additive for ASS-Li/S batteries is employed. The composite particles prepared from the hot-melt kneading process show larger particle sizes, less fine conductive additive particles, and better flowability than the simple mixture. The obtained composite particles have a matrix-type structure, in which conductive additive particles exist even inside the sulfur particles. Concerning the electrochemical performance, compositing sulfur and a conductive additive using the hot-melt kneading process improves the electrochemical performance because of the matrix-type structure of the composite particles. Moreover, by estimating the productivity of the process, the study demonstrates that the hot-melt kneading process has a significantly better productivity compared with conventional compositing processes.

To date, organic–inorganic hybrid perovskite solar cells (PSCs) have reached a certified efficiency of 25.7%, showing their great potential in industrial commercialization. However, defects at the surface and grain boundaries hinder their device performance and long-term stability. Herein, long-chain dodecylammonium halides (DACl, DABr, and DAI) to treat the perovskite surface and improve the device performance are introduced. It is found that the three passivators can all form 2D perovskites but with different halide compositions. The DACl-treated perovskite forms a pure chloride DA2PbCl4 2D perovskite, while the DABr and DAI-treated surfaces form a pure iodide DA2PbI4 2D perovskite. Compared with the DA2PbI4 layer, it is found that the DA2PbCl4 passivation layer can more effectively passivate defects, improve carrier separation at the perovskite surface, and optimize the energy alignment between the perovskite film and hole transport layer. As a result, a champion power conversion efficiency of 23.91% is achieved for the DACl-treated PSCs. Moreover, the device maintains around 95% of its initial efficiency after 1000 h storage under relative humidity of 10% at 25 °C.

Multijunction solar cells combining III–V and Si materials can provide high photoelectric conversion efficiency. Two-terminal III–V//Si triple-junction solar cells with an efficiency of 35.9% have already been developed using metal–organic vapor-phase epitaxy and the direct wafer bonding technique. This study, however, proposes the low-cost fabrication of III–V solar cells using hydride vapor-phase epitaxy (HVPE). GaInAsP solar cells are fabricated using HVPE to apply to middle cells in III–V//Si triple-junction structures. By controlling the partial pressure of the precursors, the optimal bandgap energy of 1.5 eV is obtained for the HVPE-grown GaInAsP quaternary alloys. The 1.5 eV GaInAsP single-junction solar cells show higher open-circuit voltage than the HVPE-grown GaAs solar cells. The open-circuit voltage of the GaInAsP solar cells fabricated with a GaInAsP growth rate of 77.6 μm h−1 reaches 1.1 V upon the formation of the rear-heterojunction structure. In addition, the external quantum efficiency spectra of the HVPE-grown GaInP/GaInAsP dual-junction solar cells show that the 1.5 eV GaInAsP solar cells are superior to the GaAs solar cells in terms of current matching for subcells in the III–V//Si triple-junction structures.

Precise synthesis of high-quality, sophisticated heterostructures by ordered assembly of small nanomaterials is a key step to gain advanced materials that have elaborate functionalities, collective properties, and enhanced stabilities for mitigating the energy and environment crisis. Intricating in the structure, size, and shape of nanomaterials, ordered assembly of isotropic or anisotropic nanoscale building blocks to create specified heterostructures remains challenging, owing to the extraordinary challenges in design of lattice topology of distinct nanounits and in control of their crystallization, growth, and assembly mechanism/kinetics. Herein, the emerging methodologies to prepare a diversity of ordered heterostructures with strengthened particle–particle interaction are examined and synergistic properties are enhanced. It is aimed to unlock the principles to regulate the geometrical and electronic properties of these intriguing kinds of heterostructures for respective sustainable energy and environmental applications. Current challenges and opportunities in customization of ordered heterostructure at the nanoscale and atomic level are also discussed.

Decades of studies on thermoelectric materials have enabled the design of high-performance materials based on basic materials properties, such as bandgap engineering. In general, bandgap energies correspond to the temperature at which the peak thermoelectric performance occurs. For instance, CuGaTe2 with a relatively wide bandgap of 1.2 eV has its peak zT > 1 at > 900 K. On the other hand, the zT is usually very low (<0.1) for this material at room temperature. This severely limits its average zT and hence overall performance. In this study, a phase diagram-guided Sb alloying strategy to improve the low-temperature zT of CuGaTe2 is used, by leveraging on the solubility limits to control the formation of the microstructural defects. The addition of Sb simultaneously improves the electrical conductivity and decreases the lattice thermal conductivity. For a low-temperature range of 300–623 K, this Sb-alloying strategy enables the achievement of a record high average zT of 0.33. The strategy developed in this study targets the improvement of the low-temperature range of CuGaTe2, which is rarely focused on for wide-bandgap ABX2 compounds, opening up more opportunities for holistic performance improvements, potentially enabling ultrahigh-performance thermoelectrics over a wide temperature range.

The demand of green hydrogen, that is, the hydrogen produced from water electrolysis, is expected to increase dramatically in the coming years. State-of-the-art proton exchange membrane water electrolysis (PEMWE) uses high loadings of platinum group metals, such as Pt in the electrode where hydrogen is produced. Alternative electrodes based on phosphides, sulfides, nitrides, and other low-cost alternatives are under investigation. Herein, a simple process for the preparation of RuP electrodes with high activity for the hydrogen evolution reaction (HER) in acidic electrolyte is described. A straightforward one-pot synthesis that yields RuP nanoparticles with fine-tuned composition and stoichiometry is presented, as determined by multiple characterization techniques, including lab- and synchrotron-based experiments and theoretical modeling. The RuP nanoparticles exhibit a high activity of 10 mA cm−2 at 36 mV overpotential and a Tafel slope of 30 mV dec−1, which is comparable to Pt/C. Moreover, a RuP catalyst-coated membrane (CCM) with a low Ru loading of 0.6 mgRu cm−2 is produced and tested in a PEMWE cell configuration, yielding 1.7 A cm−2 at 2 V.

Phase-change materials are of great interest in solving mismatch between energy supply and demand. However, the vulnerability of solid–liquid phase-change materials to leakage during the phase-change process limits their development and application in practice. Herein, the enhancement of the shape stability of phase-change materials is achieved through an organic–inorganic composite. The mixture of phenolic resin and polyethylene glycol forms a homogeneous solution based on their excellent mutual solubility and is able to be adsorbed into the pores of the expanded graphite by means of a vacuum-impregnation strategy. The 3D cross-linked network structure of phenolic resin is formed within the pores of expanded graphite, enabling in situ encapsulation of polyethylene glycol. It is worth noting that the curing reaction of phenolic resin is able to be initiated by heating up without the addition of any curing agent and other auxiliary materials. A thermal conductivity enhancement of 20 times than that of polyethylene glycol is achieved along with a photothermal conversion efficiency of 63.72% and with a latent heat of 134.94 J g−1 without leakage.

The recovery of noble metals is crucial in terms of resource utilization and ecological environment. Herein, a green strategy for the recovery of three noble metals, Au, Ag, and Pt, by photoelectric deposition at the cathode without external voltage is described. The realizability and mechanism of noble metals deposition are investigated and analyzed in terms of the band structure and the reduction potential of metal ions using the special heterostructure ZnO/ZnS composites derived from metal–organic frameworks, as well as ZnO and Fe2O3 semiconductors. It is found that ZnO/ZnS has preferable photoelectrochemical performance than pure ZnO due to their effective electron–hole separation and appropriate band matching structure. To deposit metals Au, Ag, and Pt, the potential of electrons in the conduction band of ZnO/ZnS should be more negative than the reduction potential of these metals, allowing for the deposition of these metals while simultaneously undergoing an oxygen evolution reaction, mediated by the photogenerated holes on the surface of the photoanode, and the collection of conduction band electrons by the back electrode.

Perovskite Photovoltaics

The stress of GaInP/GaAs/InGaAs triple-junction (3J) solar cells with different thicknesses of Cu thin-film substrates is analyzed. X-ray diffractometer and metallographic examination show that the unstable as-deposited Cu film undergoes room-temperature self-annealing, which results in grain growth and changes the internal stress of the Cu film over time. A suitable Cu thickness (18 μm) for 3J solar cells is obtained, whose internal stress can offset the stress caused by the epitaxial mismatch. The flexible 3J solar cell with 18 μm Cu film has the lowest curvature of 8.24 m−1 under the combined effect of thermal stress and lattice mismatch stress. The photovoltaic conversion efficiency reaches 35.02% with the open-circuit voltage of 3.03 V under AM1.5G spectrum. Cu films with a thickness of 14–28 μm have little effect on the optoelectronic properties of the final device. Reducing the curvature of lattice-mismatched GaInP/GaAs/InGaAs solar cell devices is beneficial for realizing large-scale flexible solar cell modules.

Lithium–sulfur (Li–S) batteries are regarded as promising candidates for high-energy storage devices because of their high theoretical energy density (2600 Wh kg−1). However, their practical applications are still hindered by a multitude of key challenges, especially the shuttle effect of soluble lithium polysulfides (LiPSs) and the sluggish sulfur redox kinetics. To address these challenges, varieties of catalytic materials have been exploited to prevent the shuttle effect and accelerate the LiPSs conversion. Recently, molybdenum-based (Mo-based) catalytic materials are widely used as sulfur host materials, modified separators, and interlayers for Li–S batteries. They include the Mo sulfides, diselenides, carbides, nitrides, oxides, phosphides, borides, and metal/single atoms/clusters. Here, recent advances in these Mo-based catalytic materials are comprehensively summarized, and the current challenges and prospects for designing highly efficient Mo-based catalytic materials are highlighted, with the aim to provide a fundamental understanding of the sulfur reaction mechanism, and to guide the rational design of cathode catalysts for high-energy and long-life Li–S batteries.

Silver selenide (Ag2Se) is a high-performance thermoelectric (TE) material near room temperature. This research improves its TE figure-of-merit (ZT) by varying the sintering temperatures (423–723 K) in the spark plasma sintering (SPS) process with high compression pressure (300 MPa). The SPS compaction of Ag2Se powders synthesized by wet chemical reaction leads to the fast fusion of particles so that the grain boundaries are hardly visible. Furthermore, the fast fusion causes nanopores at the grain surface and some cracks, particularly at higher sintering temperatures. These featured microstructures decrease carrier concentrations and affect the TE properties significantly. The TE measurements show that increasing sintering temperatures results in decreased electrical conductivity and increased magnitude of the Seebeck coefficient due to microstructural defects. Increasing SPS temperatures also suppresses the thermal conductivity from enhancing phonon scattering by defects. The bulk Ag2Se sample sintered at 723 K shows the best TE performance with the maximum ZT of 0.90 with a slight variation from 300 to 400 K. Thus, the high-temperature SPS with high-compression pressure is likely to be the key for fabricating bulk Ag2Se with high TE performance.

The burgeoning energy demand necessitates the demand for alternative sources of energy worldwide. The development and enhancement of energy storage devices are the main focus of researchers for sustainable energy production. Carbon supercapacitors have the potential applicability as a commercial source of power. Carbon-based materials have been synthesized by utilization of ionic liquids (ILs). ILs exhibit unique properties, making them valuable materials to be utilized as a precursor, template, reaction media, and electrolytes for forming carbon-based materials and enhancing supercapacitors (SCs) performance. This review article provides detailed information about ILs in the field of SCs. First, different attractive properties are illustrated, and then the role of ILs in producing carbon-based materials in the SCs field is described. The next part provides detailed information regarding the utilization of ILs as electrolytes in carbon-based SCs. Further, the implementations of ILs as electrolytes in different carbon-based materials (such as activated carbon, graphene carbon nanotubes, and carbon nanofibers) in SCs are listed. Lastly, the importance of IL-based materials from other materials and future prospects are provided to the readers, which helps further improve the sustainable development of SCs.

Li-ion batteries (LIBs) have been widely used in portable electronic devices, the transportation sector, and grid storage. However, LIB anodes are restricted to carbon-based materials limiting their energy density. Recently, the use of metallic Li as the anode in Li-metal (LMBs) and solid-state (LMSSBs) batteries has gained attention due to the high energy densities it can provide. Herein, the research progress in the field to derive a broad picture of the technologies relying on Li metal as the anode is critically assessed. It is essential to understand the Li plating and stripping processes in terms of fundamental electrochemical and physical mechanisms to address the challenges of employing metallic Li. Anode-free Li-metal batteries (AFLMBs) and anode-free solid-state batteries (AFSSBs) are the most attractive systems discussed in this review. AFLMBs are highly studied, but safety concerns due to Li dendrite growth and side reactions between plated Li metal and liquid electrolyte are some key challenges yet to be resolved. AFSSBs are the ultimate goal in this field, as utilizing a solid-state electrolyte (SSE) can prevent dendrites at moderate charging rates and realize the potential of the anode-free battery. However, the general problems with the use of SSEs remain and require substantial research efforts.