Sustainable Energy & Fuels最新文献

Seawater electrolysis powered by surplus renewable energy has garnered significant attention as part of global efforts towards carbon neutrality and climate change mitigation. Current mainstream seawater electrolysis primarily relies on alkaline or acidic electrolytes, which presents ongoing challenges due to high costs and substantial maintenance requirements. As a result, neutral seawater electrolysis is emerging as a more attractive alternative, given its abundance. However, this approach remains a challenge due to the high salt content of seawater. In this work, we report the direct laser-induced synthesis of medium-entropy alloy nanoparticles (MEA NPs), FeNiCoRu, as a bifunctional electrocatalyst for neutral seawater electrolysis. The unique features of direct laser induction, including ultrahigh temperature and rapid heating/cooling rates, enable the formation of homogeneous FeNiCoRu MEA NPs without phase separation. The FeNiCoRu MEA NPs exhibit the highest catalytic activity for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) among their single, binary, and ternary counterparts. Specifically, overpotentials of −0.368 V and −0.448 V are required for the HER, while overpotentials of 0.559 V and 0.652 V are needed for the OER to deliver current densities of 10 mA cm⁻² and 50 mA cm⁻², respectively. When assembled into an electrolyzer, FeNiCoRu‖FeNiCoRu demonstrated an notable stability, with a voltage increase of only 0.161 V after 270 hours of continuous operation. The enhanced performance is attributed to the synergistic effects of the multi-elemental composition, particularly the role of Ru in reducing reaction barriers. Our findings demonstrate that direct laser-induced synthesis is a viable approach to develop advanced multi-component electrocatalysts, presenting a feasible solution for efficient neutral seawater electrolysis and the large-scale generation of green hydrogen.

Electrochemical supercapacitors and the electrochemical oxidation of biomass-derived oxygenates have great significance for long-term high-performance devices. However, appropriate sites with redox features remain a bottleneck for electrochemical oxidation and capacitance retention. Herein, N-doped carbon sheets with Mn-phosphate-doping and Co-metal nanoparticles were synthesized via a facile one-pot activation and calcination of the layered potassium phthalimide salt without inclusion of any additional activators or template. The unique 2D-structure of the obtained microporous carbon flakes with a layered structure provides a sturdy N-C matrix for prolonged charging/discharging with abundant active adsorption sites and an effective route for rapid electrolyte ion transport with a shorter diffusion distance for the adsorption/desorption of ions. Through these merits, K-Ph-NC offers high capacitance and outstanding rate performance with an incredible energy density in capacitor devices, and the specific capacitance of the as-prepared K-Ph-NC is proportional to the number of micropores. K-Ph-NC was further transformed to a K-Ph-Oxide, a graphene oxide version of K-phthalimide, by using an improved Hummer's method by using Mn-salt and phosphoric acid, which resulted in a phthalimene oxide doped with Mn-phosphate. In addition, a composite of K-Ph-NC with ZIF-67 was thermally calcined at 700 °C under an Ar atmosphere, which resulted in e-ZIF-67/K-Ph-NC with an etched surface. A comparative electronic and structural analysis followed by a capacitance retention and electrochemical oxygen evolution reaction study revealed the role of Co-nanoparticles as compared to the Mn-phosphate doping in the resulting materials. A symmetric supercapacitor device exhibited a maximum SE value of 22.7 W h kg⁻¹ with a maximum SP of 10 416.7 W kg⁻¹, which is mainly due to the favorable microporous pore architecture in e-ZIF-67/K-Ph-NC as compared to K-Ph-NC and K-Ph-Oxide. This highlights the role of cobalt nanoparticles in e-ZIF-67/K-Ph-NC with an etched outer surface. A promising overpotential of 450 mV at 10 mA cm⁻² in the OER by e-ZIF-67/K-Ph-NC can be correlated to the charge transfer resistance across the electrode–electrolyte interface.

Formic acid and formate are among the most promising candidates for hydrogen energy carriers that can be produced from carbon dioxide. As previously reported, H₂ production based on catalytic formate decomposition involves two major issues: the use of strong acidic formate with relatively low pH and reaction control after catalyst addition. To address these two issues, visible-light controlled H₂ production from formate with the combination system of a biocatalytic process with formate dehydrogenase from Candida boidinii (CbFDH) and a photoredox reaction of water-soluble zinc porphyrin, methylviologen and colloidal platinum nanoparticles dispersed in polyvinylpyrrolidone (Pt-PVP) was developed. By using this system, the yield for formate to H₂ was estimated to be ca. 92% after 25 h irradiation.

In recent years, MOF-derived materials, especially MOF-derived oxides, have gained significant popularity and have been widely used in various applications, including energy conversion, due to their tunable structure, high specific surface area, tailorable pore volume and excellent stability. However, several challenges remain that require urgent solutions in the field of MOF-derived oxides for water splitting applications, particularly the optimization of synthesis, conversion rate and time and deactivation over a period of time. Researchers have reported various techniques to address these hurdles. This review begins with the basic principles, mechanisms, and evaluation parameters of electrochemical water splitting. It then focuses on recent findings, highlighting the contribution of different structures to enhance the overall performance of the material. Subsequently, it discusses typical performance enhancement strategies such as incorporation of high electronegative atoms, construction of heterostructures, hybridization of different materials, development of rapid mass transport, and construction of bimetallic centers. Finally, we conclude with a summary and future outlook on the field of MOF-derived oxides in water splitting applications.

This work investigated the production of renewable hydrocarbons from cottonseed oil using catalytic cracking. In a continuous fixed bed reactor, cottonseed oil was catalytically upgraded to light olefins using HZSM-5 zeolite modified with 6 wt% La. The physicochemical characterization of both catalysts was carried out using XRD, BET, NH₃-TPD, DSC-TGA, and FT-IR techniques. The amount of La doped into the microporous HZSM-5 catalyst was altered to optimize its structure and characteristics. The catalytic behavior of cottonseed oil during its decomposition was investigated using a redesigned HZSM-5 catalyst incorporating a rare-earth metal, i.e., lanthanum, in its lattice. The new synthesized catalyst (6 wt% La/HZSM-5) showed improved characteristics in terms of activity along with a reduced reaction condition compared to those of the HZSM-5 catalyst. A significant decrement in the reaction temperature for high cottonseed oil conversion was observed, and the La-doped catalyst showed considerable activity and anti-coking performance compared to the HZSM-5 catalyst. In a time-on-stream experiment conducted at 500 °C for three hours, the optimized conditions produced the maximum light olefin yield (27 wt%) over 6 wt% La/HZSM-5. Considering several olefinic products, propylene–ethylene is noteworthy, whereas CO, CH₄, and hydrogen are among the main gaseous components of the reaction, as confirmed by GC-FID, GC-TCD, GC-MS, and ¹H NMR studies. The study recorded the effect of operational parameters, including temperature and GHSV (0.038–0.38 h⁻¹), on the yield of different compounds. Hence, the catalytic decomposition of cottonseed by microporous zeolite into valuable chemicals could be promising.

Conventional electrolytic systems (e.g., water electrolysis) which rely on the anodic oxygen evolution reaction (OER) are hindered by sluggish anodic kinetics and high energy demands. Electrocatalytic aldehyde oxidation, which has low oxidation potentials, has emerged as a promising anodic reaction to be coupled with a diversity of electroreduction reactions such as the hydrogen evolution reaction, oxygen reduction reaction, nitrate reduction reaction and carbon dioxide reduction reaction. This approach not only overcomes the limitations of traditional electrolysis but can also achieve production of H₂ at the anode, thus enhancing the H₂ production efficiency and energy utilization. In this minireview, we delve into the reaction mechanisms of electrocatalytic aldehyde oxidation, examining the interplay between low-potential and high-potential reaction pathways and their impact on reaction kinetics. Furthermore, we discuss the latest developments in catalyst design, with a focus on Cu and their alloys/composites, highlighting innovative strategies to improve catalytic efficiency, stability and selectivity. In terms of application, the coupling of electrocatalytic aldehyde oxidation not only holds significance for H₂ generation but also offers new pathways for synthesizing valuable chemicals, thereby promoting the advancement of renewable energy and green chemistry.

Understanding the integration potential of direct air capture (DAC) with carbon utilisation processes can help pave the way for DAC to become an essential part of the solution towards carbon neutrality. In this study, we provide a detailed technical assessment of an integrated system using direct air capture based on temperature-vacuum-swing-adsorption (TVSA-DAC) as the carbon source for e-methanol production. The integration potential is evaluated in terms of technical compatibility, heat integration, water management, and overall energy efficiency. A specific focus is given to the TVSA-DAC process considering the uncertainty of the available adsorption mass transfer kinetics. It is found that the CO₂-productivity ranges from 0.23–13.35 kg_CO2 m⁻³ h⁻¹ given an interval for the CO₂ mass transfer coefficient of 0.0001–0.1 s⁻¹ in which the highest productivity is obtained using a steam sweep during desorption. The potential to achieve a steady CO₂ output from the TVSA-DAC is proven; however, the complexity of the integrated design configuration depends greatly on the adsorption kinetics. Generally, a well-aligned heat integration with no external heat demand for the combined system can be achieved using high-temperature heat pumps to facilitate favourable heat recovery from the electrolysis. Furthermore, the integrated system can be water self-sufficient and even net producing at a relative humidity above 50% due to the co-capture of water in the TVSA-DAC process. The overall energy efficiency can reach up to 52% for the integrated system.

Earth-abundant carbon-based materials have been explored as efficient, low-cost, metal-free alternatives to platinum and transition metal-based electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells and metal–air batteries. In contrast to conventional methods for the synthesis of metal-free catalysts relying on carbon nanotubes and graphene with inadequate porosity, herein, we report the synthesis of an N,S-dual-doped porous carbon (N,S-PC) catalyst derived from a polypyrrole (PPy) hydrogel impregnated with suitable N,S doping agents. The catalyst with the optimum structure and composition (N,S-PC(TS)) was obtained using thiosemicarbazide as the doping agent. This catalyst demonstrated excellent ORR activity in 0.1 M KOH with a positive onset (E_on) and half-wave (E_1/2) potential of 0.940 V and 0.825 V vs. RHE, respectively, which are close to those of Pt/C. In addition, the catalyst manifested excellent short-term stability, retaining 78% of its original current for 25 h and superior stability during potential cycling experiment. This catalyst displayed good selectivity towards the 4e⁻ ORR process with a low H₂O₂ yield (≤8.5%) in the potential range 0.4–0.1 V. Through this work, we attempt to popularize organic polymer hydrogel substrates having abundant nitrogen and unique three-dimensional network structures for the design of metal-free carbon catalysts for electrochemical energy applications.

Metal borates have long-lasting uses due their high electrical conductivity and stability. The exothermic solid-state synthesis (SSS) reaction between ammonium molybdate and (NH₄)₂B₄O₇ produces molybdenum/molybdenum borate (Mo@Mo-6Bo) with a lamellar labyrinth-like morphology. The integration of boron into transition metal (Mo) matrices with borate layers and defect-rich lattices and grain boundaries induced strong interaction between the electrolyte and the catalytic sites; it enhanced the absorption–desorption of intermediates to boost catalytic efficiency. The regulation of electronic structure and fast charge transfer on Mo@Mo-6Bo augmented the kinetics of the oxygen evolution reaction (OER) as evidenced by low overpotential (GC/NF) of 271/221 mV. A small Tafel slope of 63/58 mV dec⁻¹ and high performance were maintained over 24 h/50 h @ 10 mA cm⁻². The Mo@Mo-6Bo-based electrolyzer required 1.56 V in the alkaline electrolyte to reach 100 mA cm⁻², and high performance was maintained over 50 h. This alternative process was used as an anode to produce carbon-negative green H₂ and for value-added electrolysis, thereby exploiting economic benefits and converting waste into renewable resources. This work provides an efficient strategy that can be extended to develop a wide range of electrodes by replacing the sluggish OER for renewable electrochemical energy conversion.

Graphitic carbon nitride (g-C₃N₄) is a metal-free semiconductor material with highly promising photocatalytic properties owing to its unique structural, electronic, and optical characteristics. Herein, the solvothermal synthesis of g-C₃N₄ as a photocatalyst for photoelectrochemical water splitting and the photocatalytic degradation of organic pollutants is reported. The solvothermal synthesis of g-C₃N₄ was carried out using acetonitrile as the solvent at three different temperatures: 160 °C, 180 °C and 200 °C. The chemical structure of the synthesized photocatalysts was characterized using NMR, FT-IR, and Raman spectroscopy. Phase purity was confirmed through X-ray diffraction (XRD), and the morphology was analyzed using transmission electron microscopy (TEM). The optical properties were accessed using UV-visible and diffuse reflectance spectroscopy (DRS). The prepared photocatalysts were tested for photoelectrochemical (PEC) water splitting and the photocatalytic degradation of organic pollutants, with methylene blue used as a model compound. It was observed that the g-C₃N₄ synthesized at 200 °C showed an enhanced anodic photocurrent of ∼25 μA cm⁻² at an applied potential of 1.7 V vs. RHE under exposure to 100 mW cm⁻², AM 1.5 G. Additionally, it exhibited superior performance in the photocatalytic degradation of organic pollutants, with methylene blue as the model compound. The enhanced photoelectrochemical and photocatalytic performance of the g-C₃N₄ synthesized at 200 °C is likely attributed to the improved physicochemical properties of the material, which are linked to its structural features modified by the elevated synthesis temperature.