High entropy alloys (HEAs) are composed of five or more metal elements with similar proportions. Due to the electronic structure among metal elements, they have abundant active sites and have good catalytic activity and stability as materials. Therefore, they have great promise in electrochemical energy storage and electrocatalysis. This paper reviews the preparation and characterization methods of HEAs, and the applications of HEAs in catalysis, especially the contribution in lithium-sulfur batteries, but also in Electrolyzed water and other energy storage materials. The challenges of HEAs in catalysis and their future developments are also presented.

In recent years, photorechargeable Li-ion batteries (Li-PRBs) are investigated as potential energy devices to supply continuous power to remote IoT or electronic devices. These Li-PRBs, due to their lightweight and low-cost, offers various advantages compared to conventional combination of solar cells and a battery. Single active material-based PRBs have gained attention due to the use of multifunctional materials which perform both solar energy harvesting and storage, however most of the PRBs studied so far are based on ion intercalation. Herein, the use of conversion type active material α-Fe2O3 for efficient and stable operation of Li-PRBs is demonstrated. Cost-effective solution processing method is used to synthesize α-Fe2O3 nanorods (NRs), which form nanoporous morphology when blended with Multi-walled carbon nanotubes / Phenyl-C61 butyric acid methyl ester (MWCNT/PCBM) conducting additives to form photocathodes. α-Fe2O3 NRs shown simultaneous solar energy harvesting in visible region of spectra, owing to its energy bandgap Eg ≈ 2.1 eV, and efficient Li-ion storage via conversion reaction mechanism. Li-PRB has shown photoconversion and storage efficiency of ≈1.988% when illuminated with blue LED (λex ≈ 470 nm) for large voltage window (0.8–2.57 V). The use of conversion type material like Fe2O3 in PRBs opens up new pathways to explore new materials and mechanisms for these emerging devices.

With increasing energy demands and environmental issues, renewable energy-related conversion systems have gained significant attention as a potential substitute for traditional fossil fuel-based energy technologies. First introduced by S.W.Grove in 1838, fuel cells have been extensively developed into many different types, and direct alcohol fuel cells (DAFCs) are of interest as a potential power source because of their large power density, quick start, simplicity, and nearly zero emission. However, the high cost and poor catalytic efficiency of current catalysts are primary barriers to commercializing DAFCs. Designing advanced nanocatalysts for both anode and cathode electrodes is of crucial importance for practical DAFC development; however, a brief evaluation of current progress in electrocatalyst development for the alcohol oxidation reaction (AOR) and oxygen reduction reaction (ORR) is still very little. Herein, recent advances in fuel cell catalysts, mainly focusing on several most active areas (i.e., Pt- and Pt-free-based catalysts, metal-free carbon, carbon-based nonprecious metal composites) are concisely summarized. Also, challenges and prospects for DAFCs are highlighted to supply a comprehensive view for further designing high-performance DAFC catalysts.

Organic supercapacitors are considered attractive alternatives to traditional inorganic-based charge storage devices due to their synthetic versatility, low cost, and environment-friendliness features. Photopolymerized anthraquinone-polydiacetylene is employed as a core component in high-performance asymmetric supercapacitors (ASCs). Specifically, interspersed polydiacetylene-anthraquinone/polyaniline (PANI) electrodes are prepared via drop-casting and used as cathodes in devices employing polypyrrole/reduced graphene oxide anodes using aqueous or ionic liquid electrolytes. The excellent electrochemical properties of the polydiacetylene-anthraquinone/PANI electrodes, specifically high capacitance (specific capacitance ≈720 F g−1 at 1 A g−1), long discharge time, and cycling stability, are ascribed to the superior redox profile of the anthraquinone and ambipolar charge transport associated with the polydiacetylene framework. The asymmetric supercapacitor prepared using the polydiacetylene-anthraquinone/PANI electrodes displays a high energy density of 36 Wh kg−1 at a power density of 995 W kg−1, underscoring possible utilization of the anthraquinone-polydiacetylene derivative in practical energy storage devices.

Plastic waste (PW) from textile and construction industries is rarely recycled due to the lack of economical and effective commercial recycling technologies. In this work, PW from these two sources is successfully converted into a microporous sorbent that is highly selective to carbon dioxide (CO2) adsorption. The synthesis of the sorbent is achieved by the pyrolysis of PW in the presence of a potassium salt activator. The properties of the sorbent can be tuned by changing the parent plastic type to get varying degrees of microporosity, surface area, and nitrogen content. The best performer, a sorbent derived from nylon 6,12, had a CO2 uptake of 19 wt% (4.32 mmol g−1) and 5 wt% (1.1 mmol g−1) at 1 and 0.1 bar, respectively. The initial estimated cost of synthesizing the sorbent is ≈$531 tonne−1 of PW making this process economically attractive compared to competitive technologies. The sorbent effectiveness in CO2 separation is demonstrated from various feeds including simulated flue gas and direct air capture. Thus, this upcycling approach can help to address two environmental challenges: PW pollution and increased atmospheric CO2 levels.

Reducing carbon dioxide to value-added chemicals by electrolysis is a promising strategy to substitute fossil-based processes. Research on CO2 electrolysis has vastly progressed, focusing on catalysis and electrode design, leaving an essential question on the central part of the electrolyzer: Which type of ion exchange membrane is best suited for CO2 electrolysis from an economic perspective? To address this question, holistic process optimization of CO2 reduction and product purification is applied. The findings demonstrate that CO2 electrolysis with an anion exchange membrane shows competitive production costs for CO of 796 €/tCO, outperforming cation exchange and bipolar membranes. Unlike often described, the CO2 pumping effect does not significantly impair the economics but offers an efficient indirect regeneration of dissociated CO2. Furthermore, the results emphasize selective reduction of CO2 rather than co-electrolysis of CO2 and H2O. While pointing to a positive economic perspective, life-cycle assessment highlights the need to minimize CO2 emissions related to electricity consumption and incomplete CO2 utilization.

There is a need to generate micro-scale indicators to measure progress towards meeting Sustainable Development Goals (SDGs) 6 and 8. In this sense, this study applies Social Life Cycle Assessment, including Quality of Employment (QoE) and Adequate Public Water Supply (AWS) indicators to assess the social performance of Mexico City's water cycle to identify the level (low, medium and high) of the potential risk of social impact (PR). The results show that the labor hours (WH) required by 1m3 of water in Mexico City is equivalent to 0.062 WH. The QoE indicator shows that 94% of WH are associated with high PR due to low wages. For AWS, 5% is associated with a high PR for local communities in the Cutzamala system due to poor water quality and consumption of bottled water. This case study demonstrates that progress on QoE and AWS indicators can significantly contribute to achieving SDGs 6 and 8 in the water management of communities involved in Mexico City's water cycle.

Biodegradable Polymers

The severe capacity loss of spinel LiMn2O4 (LMO) limits the utility of this otherwise promising lithium ion battery cathode material. One of the strategies to mitigate capacity fade is applying a coating on LMO particle surfaces. While this approach yields promising results, there is limited understanding of mechanisms whereby coatings improve LMO capacity retention. Herein, the effects of a new protective coating material, La0.5Sr0.5CoO3 (LSCO), in a thin-film battery geometry that is amenable to fundamental studies of electrode processes, are reported. RF sputtering deposition is used to produce high quality 25–100 nm LMO cathodes on Al2O3 substrates with an intervening Pt/Ti back-side contact layer. Cycling of the un-coated cathodes results in capacity loss of 18% over 300 cycles. Adding a 2 nm LSCO layer reduces the capacity loss to 3%. While this may be due in part to reduced Mn dissolution, scanning transmission electron microscopy results indicate that the coating helps to preserve crystallinity and reduce lattice structure distortion due to inhibited formation of defect tetragonal spinel. Three-electrode electrochemical impedance spectroscopy results reveal that the LSCO coating increases charge transfer and ohmic resistances, but the increases are generally too small to significantly impact cell performance even at high C-rates.

Bismuth sulfide has become an attractive candidate in the electrocatalytic oxygen evolution reaction (OER), owing to its open coordination sites, unpaired electron orbitals, and mild electronegativity, but its OER performance is hindered by many deficiencies. The combination of heteroatom construction and vacancy engineering has been used to improve the OER performance of bismuth-based electrocatalysts, but few studies can clearly describe the roles of dopants and vacancies in improving OER performance. Herein, N dopants and S vacancies in Bi2S3 nanorods via one-step NH3/Ar plasma etching to investigate the enhanced OER performance are constructed. N dopants and S vacancies both regulated the intrinsic charge ordering of Bi2S3 nanorods, enhancing the p-band center and Fermi level while also boosting the electroconductivity and wettability of the material. In addition, density functional theory calculations suggest that N doping promoted the adsorption of Bi sites, while S vacancies favored the desorption of S sites. Under the synergistic effects of N dopants and S vacancies, Bi2S3-based electrocatalysts exhibited a low overpotential of 374 mV at 10 mA cm−2 and satisfactory durability, demonstrating a feasible strategy for exploiting main group element OER electrocatalysts.

The oxygen evolution reaction (OER) has proved to be a hard-to-overlook impediment for the development of water splitting devices, metal-air batteries, or photo-electrochemical cells, to name but a few. Electro- and photo-electrocatalysts, designed using inexpensive materials, that demand low overpotential values to smoothly drive OER in either electrolyzer devices or proton-exchange membrane cells, as well as withstand harsh conditions and repetitive cycling, are fervently desired by the industry. Transition metal dichalcogenides (TMDs), namely MoS2, WS2, MoSe2 and WSe2 as the main representatives, especially when engineered via exfoliation methods, have been highlighted as modular scaffolds for electrocatalytic applications, owed to their ability to have their intrinsic characteristics fine-tuned. In this review, the goal is to highlight the role of exfoliation, as a means of ability engineering, by presenting significant works where these TMDs constitute the core part for OER-catalyzing nanohybrid systems.

The coordinatively unsaturated metal sites (CUMSs) have attracted widespread attention for enhancing catalytic activity. This study reports a controllable “bibonding” method to construct the coordinatively unsaturated Zni+ (0 < i < 2) active sites by forming N(g-C3N4)-Zn—N(imidazole) under mild experimental conditions. The catalysts with Zni+ are used for the photo-Fenton reaction to degrade methylene blue (MB) without any oxidant. The degradation efficiency is positively correlated with Zni+. The Zni+ improved the Fe2+/Fe3+ conversion efficiency and the H2O2 generation ability of the catalyst. The optimized catalysts with 2.27% of Zni+ present a photo-Fenton degradation efficiency of MB as 73.45 mg g−1 at pH 7 and 78.54 mg g−1 at pH 4. This strategy can be used to construct CUMSs for a series of narrow bandgap semiconductor materials containing nitrogen atoms.

Polymeric materials are usually tailored for specific functionality. A single polymer exhibiting multiple simultaneous functionalities often requires intricate molecular architecture, which is difficult to manufacture at scale because of its complex synthesis routes. Herein, a facile, partly renewable composition―prepared via reactive melt processing―that induces tunable functionalities such as 3D printability, shape recovery, and self-healing while exhibiting satisfactory mechanical properties is reported. The system with a hydrogen-bonded 3D network consists of thermally reversible nano-scale agglomerates of sustainable, rigid phenolic oligomers and crystallizable flexible polymer. Local molecular mobility and temperature-dependent relaxation and recovery of the non-equilibrium networked states enable exploiting these simultaneous functionalities. Transitions involving solidification and structure stabilization at ambient temperature spanning several hours after preheating only at 70 °C directly contrast typical thermoplastic or thermoplastic elastomer behaviors. Results from this study can inform the design of future rheology modifiers and materials for soft robotics.

Solar cells offer clean and abundant power sources for directly photo-charging rechargeable batteries, which shows great potential for the development of integrated power supply. In order to deepen the understanding of the novel type of charging process, this research takes silicon solar cells and lithium cobalt oxide batteries as examples to compare the performance difference between photo-charging and conventional constant current charging in detail. Surprisingly, the photo-charging turns out to be superior in charging efficiency, polarization mitigation, and cyclic performance even with the intrinsic instability of the solar cells when compared with constant current charging mode. Finally, this research optimizes the calculation method of energy storage efficiency in the integrated power supply by calculating the actual power during the photo-charging process by recording the voltage and current change with time. Besides, the power matching degree is quantified by the ratio of η1____ to η1, providing new ideas for the matching method of solar cells and rechargeable batteries in integrated power supplies.

Water electrolysis is a promising method for producing ultra-pure hydrogen as a sustainable energy source in the future. In this study, the use of a hollow-structured Fe-doped CoP with an abundance of phosphorus defects for both oxygen and hydrogen evolution reactions (OER and HER) is suggested. The as-prepared electrocatalyst has a low overpotential of 300 and 143 mV to achieve a current density of 10 mA cm−2 for the OER and HER, respectively. When the synthesized electrocatalyst is used as both anode and cathode in a water electrolyzer, the full cell requires a very small cell voltage of 1.63 V at 10 mA cm−2 and exhibits excellent stability for over 100 h. The excellent performance is due to the generation of numerous electrocatalytic active sites induced by introduction of structural defects such as Fe dopants and P vacancies, which modify the adsorption energy of reaction intermediates during water electrolysis. This study can offer new insights into the development of efficient precious metal-free electrocatalysts for production of renewable energy sources.

Organic–inorganic halide perovskite materials have attracted wide attention and research because of their adjustable bandgap, high absorption coefficient, and simple preparation methods. The power conversion efficiency (PCE) of single-junction perovskite cells has increased from 3.8% to 26% in recent years. Using bandgap complementary photovoltaic technology to pair wide-bandgap with low bandgap perovskites to build all-perovskite tandem solar cells (all-PTSCs) is one of the best strategies to break the limitation of Shockley-Queisser (SQ), which is expected to obtain a PCE higher than 30% at low cost. In this brief review, the structure and working principle of all-PTSCs is first introduced. Then the latest progress of each component of tandem devices is reviewed according to the two different tandem modes of 2-terminal (2-T) and 4-terminal (4-T). Besides, the existing problems and optimization strategies of different components are discussed. Finally, the future development of all-PTSCs is prospected.

Zn–air fuel cells are promising energy storage devices for renewable energy and power sources, as they are cost-effective and have high energy density. However, limited charge and discharge cycles and low round-trip efficiency have long been obstacles to large-scale market deployment. Herein, a new fluidized-bed zinc–air fuel cell is designed, constructed, tested, and characterized. The integration of the fluidized bed in the zinc–air fuel cell leads to key advantages such as: erosion of the anode passivation layer, which plays a key role in the rapid voltage decay and keeping the products of reactions away from the proximity of the electrodes, reducing the concentration overpotential, due to the concentration gradient of electrode species in the diffusion boundary layer between the electrode–electrolyte interface and the electrolyte bulk.

Greenhouses provide a controlled environment for plant growth, which increases crop yields, reduces the use of water and fertilizers, and offers resilience to droughts and extreme weather. However, greenhouse operation is energy intensive due to their heating and cooling loads. Luminescent solar concentrators (LSCs) are promising for semitransparent greenhouse roofs that produce clean electricity, thus reducing the greenhouse energy demand, while also transmitting enough light to satisfy plant growth. Here, we model the performance of LSC roofs designed as glass panels coated with quantum dot (QD)/polymer nanocomposite films and front-facing surface-mounted photovolatic cells. Five widely studied QD materials are examined to demonstrate that the proposed QD LSC roofs can have effective power conversion efficiencies exceeding 10% while also increasing the red-light fraction, which is beneficial for plant growth. The effect of LSC integration on the greenhouse thermal energy demands is studied for the example of silicon (Si) QD LSC roofs. In warm climates, solar power generated by the Si QD LSC roofs satisfies the entire greenhouse energy demand and thus enables net-zero energy operation. Overall, the results of the current research demonstrate the strong potential of integrating QD LSCs into greenhouses to reduce energy costs and enhance plant growth.

The triboelectric nanogenerator (TENG), which is suitable for low-frequency and high-entropy mechanical energy harvesting, has great advantages in ocean energy collection and potential blue energy applications. The rational structural design can ensure the best working state of TENG in complex marine environment. Herein, an unidentified flying object (UFO) shaped integrated triboelectric energy harvester (U-TENG) is proposed for complex and random ocean wave energy harvesting. The U-TENG is assembled in a vertical structure by combining a coping TENG in a rotational structure and a bottom TENG in a rolling-ball design. The proposed vertically integrated TENG structure can increase the efficiency of space utilization and improve the entirety output performance compared with the single device structure. A sophisticated auxiliary facility has also been pioneerily designed to simulate the ocean waving during the experiment tests. The prepared U-TENG can easily light up dozens of light emitting diodes and power a commercial hygrothermograph at a low operating frequency. This work provides a highly efficient means to the development of high-performance and robust TENG for ocean energy harvesting.

Single-use plastic straws are a significant environmental concern as they pollute the ecosystem and drastically harm humans and aquatic organisms. Paper straws, as an alternative have limitations such as weak mechanical properties, poor water stability, and the use of coatings or adhesives that hinder their biodegradability. The present study reports a facile approach for preparing mechanically robust, water-stable, and biodegradable straws using partially delignified and microwave (MW) treated bamboo. The MW-processed bamboo-based straws present water stability for up to 16 h and a contact angle of 87.8°, suggesting low wettability and water stability for long periods. The processed straws show improved tensile strength of 59.3 MPa, Young's modulus of 988 MPa, and a flexural strength of 13.9 MPa, along with >97% biodegradation (98 days). MW treatment is a rapid and low-cost strategy for physiochemical modification that can be used for the large-scale production of drinking straws from biomass. The life cycle analysis (LCA) shows that MW-irradiated bamboo straws generate 86.53% less global warming potential (GWP) impact during production and 91.8% less human health damage impact during end-of-life (EOL), compared to plastic straws. MW-treated drinking straws from bamboo can thus become a low-cost, eco-friendly, biodegradable, and sustainable alternative to paper and plastic straws.