Sustainable Energy & Fuels最新文献

Liquid hydrogen carriers (LHCs) are important shuttles for molecular hydrogen (H₂) as they are convenient to transport as energy-dense liquids over distances greater than 10 000 km. Herein, we provide comprehensive insights into the comparative practicality and safety of irreversible LHCs. From a gas purification standpoint, fewer products in the released H₂ stream result in less separation complexity and lower cost. Unit operational complexities of methanol (MeOH) steam reforming versus fossil steam-methane reforming were analyzed in depth to highlight gas-cleaning complexities. The main challenge is to estimate the costs of LHC reforming, cleaning and compression (RC&C) steps for H₂ production in order to break even with other energy scenarios. To achieve this, two techno-economic analyses (TEA) were performed from the ‘vehicle’ and ‘fuel’ points of view. ‘Vehicle’ analysis compares the use of MeOH-to-H₂ for proton-exchange membrane fuel-cell vehicles (FCVs) with the use of MeOH directly as drop-in fuel for conventional vehicles (ICEVs). ‘Fuel’ analysis compares renewable MeOH and dimethyl ether LHC transport with pressurized and cryogenic H₂ transport for FCVs. For the analyses in which H₂ gas is produced as a fuel, RC&C steps are assumed to be accomplished off-board or before fueling the vehicles. ‘Vehicle’ analysis findings indicate that with a moderate tax on carbon emissions, in the year 2035 and beyond, FCVs can be competitive with ICEVs with an RC&C cost of ∼US $ 2–6 per kg H₂. From the ‘fuel’ analysis perspective, LHCs break-even with gaseous and liquid H₂ transport at a more flexible RC&C cost of US $ 7.9–11.4 per kg H₂.

The photocatalytic biomass transformation into valuable chemicals and fuels is interesting but challenging. The levulinic acid (LA) to γ-valerolactone (GVL) transformation has been explored under conventional thermal conditions. Reports on the photocatalytic hydrogenation of LA to GVL are rare, obtaining comprehensive information on the complete reduction process is challenging. Herein, CeO₂ was synthesized via the hydrothermal method and decorated with varying wt% of Ru to form Ru/CeO₂. The physical characteristics of the catalysts were confirmed through PXRD, TEM, and XPS analyses. The light absorption capacity of CeO₂ and Ru-decorated CeO₂ (specifically 0.5Ru/CeO₂ and 1Ru/CeO₂) was characterized using UV-visible spectroscopy. Additionally, the band structure of CeO₂ and 1Ru/CeO₂ was examined using VB-XPS and UPS analysis. Decorating CeO₂ with Ru improved charge separation and enhanced visible light absorption capacity. The visible light active 1Ru/CeO₂ catalyst achieved ∼99% conversion of LA to GVL under 15 W blue LED illumination at 0.2 MPa hydrogen. A mechanistic investigation through control experiments revealed that electrons facilitated the reduction of the ketonic group, while C–O cleavage in the acidic group (–COOH) is by the holes, which forms a carbonyl cation or radical, followed by immediate cyclization to GVL. The findings elucidate the active sites and demonstrate the recyclability of 1Ru/CeO₂ for selective LA hydrogenation under visible light. The work is significant from a sustainable chemistry perspective and crucial for the sustainable production of valuable chemicals.

Intergrating in situ fabrication of photocatalysts with on-demand photocatalytic H₂ evolution from water splitting holds immense promise for enhancing the H₂ utilization efficiency. Herein, all amorphous TiO₂-coupled-MoS_x photocatalysts (a-TM) are in situ fabricated by hydrolyzing the Ti precursor followed by photochemical reduction of (NH₄)₂MoS₄ in the reaction solution for on-demand photocatalytic H₂ evolution reaction (HER). Thanks to the intimate contact between a-TiO₂ and the a-MoS_x cocatalyst, as well as abundant active sites on the a-MoS_x cocatalyst, the photogenerated electrons can rapidly transfer from the excited a-TiO₂ to the well-interconnected a-MoS_x, leading to efficient charge separation, thereby greatly promoting the kinetics of the HER. The as-fabricated a-TM2 with 2 mol% a-MoS_x exhibits the highest H₂ evolution rate of 696.2 μmol h⁻¹ under UV light, 2.7 times higher than that of benchmark P25 loaded with a 2 mol% a-MoS_x cocatalyst (PM2). This work introduces a new concept of in situ fabricating semiconductor-based photocatalysts for on-demand photocatalytic HER at a large scale.

Developing high-current oxygen evolution reaction (OER) electrocatalysts with low overpotential, high conductivity, high active surface area, and high stability is an attractive yet challenging process. Herein, a ternary FeCoNi hydroxide-fluoride material by doping fluoride into FeCoNi(OH)_x was synthesized through a simple electrodeposition method. The OER performance of FeCoNiF(OH)_x on a nickel foam electrode with a high surface area was associated with overpotentials of 243, 328, and 412 mV, with geometrical current densities of 100, 500, and 1000 mA cm⁻², respectively, in 1.0 M KOH solution. In addition, FeCoNiF(OH)_x exhibited high stability during controlled potential electrolysis in 1.0 M KOH at an overpotential of 243 mV for 50 h. Overall, we believe that our findings can advance the investigation of OER electrocatalysts.

The utilization of efficient and pollution-free water splitting hydrogen production technology is of great significance for alleviating environmental problems and achieving sustainable human development. The prospects of exploring highly efficient electrocatalytic activity, low-cost, and high-stability catalysts is vast, but there are still huge challenges. In this work, ZIF-67 derived Co₂(P₄O₁₂) and CoSe₂ heterostructures (Co₂(P₄O₁₂)/CoSe₂/CNFs) loaded on carbon nanofibers have been constructed using a combination of an in situ growth method and electrostatic spinning technique. The Co₂(P₄O₁₂)/CoSe₂/CNFs composite catalyst exhibited the highest oxygen evolution reaction (OER) activity (315 mV) and hydrogen evolution reaction (HER) activity (221 mV) at a current density of 10 mA cm⁻². After stability tests, the current density retention rates for the OER and HER are 96.1% and 85.6%, respectively. The combination of Co₂(P₄O₁₂)/CoSe₂/CNFs-2 was employed in a water electrolysis system, resulting in the attainment of a current density of 10 mA cm⁻² at a cell voltage of only 1.71 V. This paper provides a new idea for exploring bifunctional catalysts for water electrolysis, which has good prospects for development.

Designing high-performance bifunctional materials for photo-assisted electrochemical charge storage and photocatalysis is challenging due to the difficulty in balancing electroactivity and photo-to-electric efficiency. Herein, copper foam (CF) supported three-dimensional nanoarrays (3D NAs) composed of copper oxide/iron oxide (Cu₂O/Fe₂O₃) heterostructures were constructed as bifunctional materials for the photocatalytic CO₂ reduction reaction (CO₂RR) and photo-assisted supercapacitors. These Cu₂O/Fe₂O₃ 3D NAs have demonstrated high electroactivity and good light adsorption with high photocurrent responses. As a result, the optimized Cu₂O/Fe₂O₃ photocatalyst delivered a high methane (CH₄) production rate of 38.6 μmol h⁻¹ g⁻¹ with good cycling stability for the CO₂RR. When used for photo-assisted supercapacitors, the optimized Cu₂O/Fe₂O₃ photoelectrode exhibited a maximum photo-capacitance of 595 F g⁻¹, delivering an enhancement of 17.3% over the capacitance obtained without light (507 F g⁻¹). This work provides a unique approach to utilizing light energy directly to promote electrochemical and photocatalytic properties.

Photocatalytic production of solar fuels and high-value chemicals by photogenerated carriers has been at the forefront as one of the promising sustainable approaches. However, most of the studies focus only on one of the half reactions, either photoreduction or photooxidation, leading to underutilization of the potentiality of photocatalysis due to inefficient harvesting of electron–hole pairs. Herein, the efficient utilization of photogenerated electron–hole pairs was demonstrated by employing phosphorous-doped graphitic carbon nitride (P-doped g-C₃N₄) as a visible light-active photocatalyst that is capable of simultaneously producing hydrogen and benzaldehyde from benzyl alcohol. P-doping into g-C₃N₄ was achieved using an eco-friendly P source. P doping induced changes in the light-harvesting capacity of g-C₃N₄, and its consequence on the dual-functional photocatalytic activity of P-doped g-C₃N₄ was systematically investigated using various characterization techniques. P-doped g-C₃N₄ exhibited an ≈3-fold increase in photocatalytic activity in the production of H₂ and benzaldehyde as compared to that of pristine g-C₃N₄. Density functional theory (DFT) studies reveal that the P-dopant preferentially replaces the corner C-site as compared to the N site of the tri-s-triazine ring of g-C₃N₄, which results in the creation of mid-gap states that enable the enhanced visible light absorption of P-doped g-C₃N₄. Mechanistic investigation studies suggest that photogenerated holes drive the selective oxidation of benzyl alcohol to benzaldehyde while photogenerated electrons drive H₂ evolution, leading to concomitant production of H₂ and benzaldehyde by P-doped g-C₃N₄. The selective conversion of benzyl alcohol proceeds through a carbon-centred radical mechanism, according to experimental and DFT studies. This work elucidates the importance of P-doping in g-C₃N₄ for the simultaneous production of solar fuels (such as H₂) and high-value chemicals (such as benzaldehyde).

Liquid evaporation, or water vapor generation, is a spontaneous natural process and is always accompanied by evaporation cooling. However, evaporation cooling that can directly produce electricity based on the Seebeck effect and even supply power for electronic devices has not yet been reported. Here, liquid evaporation generators (LEGs), with cheap and practical thermoelectric generators (TEGs), are demonstrated to generate electric power based on the combination of the Seebeck effect and evaporation cooling. We systematically explored the LEG based on water evaporation (w-LEG) in a real environment, and five tandem w-LEGs can produce a maximum voltage of 4.4 V and achieve a maximum power density of 5.4 mW cm⁻², which can successfully supply power for common electronic devices. Our concepts demonstrate a new supplement of green energy technology and a new direction for the applications of low temperature thermoelectric conversion (below 50 °C).

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The electrocatalytic N₂ fixation provides a carbon-neutral and energy-efficient pathway for producing ammonia effectively under ambient conditions. However, it typically faces significant challenges in achieving a high ammonia yield and FE. This is attributed to the lack of efficient electrocatalysts that can easily activate the strong N₂ triple bond and suppress the competing HER. Metal oxides are widely acknowledged as effective electrocatalysts for nitrogen reduction reaction (NRR) because they can assist in easily activating the triple bond of N₂. Herein, we demonstrate that a mixed metal oxide, Bi₄Ti₃O₁₂, holds potential as a catalyst for electrocatalytic NRR under ambient conditions with an ammonia yield of 27.8 μg h⁻¹ mg_cat⁻¹ and FE of 22% at −0.6 V in 0.1 M HCl. The synergistic effect of the N₂ binding ability of Ti and Bi, coupled with a robust interaction of the Bi 6p band and N 2p orbitals and the low hydrogen adsorption energy of Bi collectively inhibit surface electron accessibility for the HER, thereby facilitating the easy activation of N₂ and results in better electrocatalytic activity and selectivity for NRR.