Search

Solar photoelectrochemical reactions have been considered one of the most promising paths for sustainable energy production. To date, however, there has been no demonstration of semiconductor photoelectrodes with long-term stable operation in a two-electrode configuration, which is required for any practical application. Herein, we demonstrate the stable operation of a photocathode comprising Si and GaN, the two most produced semiconductors in the world, for 3,000 hrs without any performance degradation in two-electrode configurations. Measurements in both three- and two-electrode configurations suggest that surfaces of the GaN nanowires on Si photocathode transform in situ into Ga-O-N that drastically enhances hydrogen evolution and remains stable for 3,000 hrs. First principles calculations further revealed that the in-situ Ga-O-N species exhibit atomic-scale surface metallization. This study overcomes the conventional dilemma between efficiency and stability imposed by extrinsic cocatalysts, offering a path for practical application of photoelectrochemical devices and systems for clean energy.

Light-driven bioethanol dehydration offers attractive outlooks for the sustainable production of ethylene. Herein, a surface-hydrogenated CrMnOx is coupled with GaN nanowires (GaN@CMO-H) for light-driven ethanol dehydration to ethylene. Through combined experimental and computational investigations, a surface hydrogen-replenishment mechanism is proposed to disclose the ethanol dehydration pathway over GaN@CMO-H. Moreover, the surface-hydrogenated GaN@CMO-H can significantly lower the reaction energy barrier of the C2H5OH-to-C2H4 conversion by switching the rate-determining reaction step compared to both GaN and GaN@CMO. Consequently, the surface-hydrogenated GaN@CMO-H illustrates a considerable ethylene production activity of 1.78 mol·gcat−1·h−1 with a high turnover number of 94,769 mole ethylene per mole CrMnOx. This work illustrates a new route for sustainable ethylene production with the only use of bioethanol and sunlight beyond fossil fuels. Light-driven bioethanol dehydration presents a promising route for sustainable ethylene production. This study unveils a surface hydrogen-replenishment mechanism facilitating ethanol dehydration on GaN nanowires with surface-hydrogenated CrMnOx, achieving an ethylene production rate of 1.78 mol·gcat−1·h−1. [ABSTRACT FROM AUTHOR]

Transformation of lignin to syngas can turn waste into treasure yet remains a tremendous challenge because of its naturally evolved stubborn structure. In this work, light‐driven reforming of natural lignin in water for green syngas production is explored using Pt‐decorated InGaN nanowires. The spectroscopic characterizations, isotope, and model compound experiments, as well as density function theory calculation, disclose that among a variety of groups including aromatic ring, −OH, −OCH3, −C3H7 with complex chemical bonds of O−H, C−H, C−C, C−O, etc., InGaN nanowires are cooperative with Pt for preferably breaking the C−O bond of the rich O−CH3 group in lignin to liberating ⋅CH3 by photogenerated holes with a minimum dissociation energy of 2.33 eV. Syngas are subsequently yielded from the continuous evolution of ⋅CH3 and ⋅OH from photocatalytic reforming of lignin in water. Together with the superior optoelectronic attributes of Pt‐decorated InGaN nanowires, the evolution rate of syngas approaches 43.4 mol ⋅ g−1 ⋅ h−1 with tunable H2/CO ratios and a remarkable turnover number (TON) of 150, 543 mol syngas per mol Pt. Notably, the architecture demonstrates a high light efficiency of 12.1 % for syngas generation under focused light without any extra thermal input. Outdoor test ascertains the viability of producing syngas with the only inputs of natural lignin, water, and sunlight, thus presenting a low‐carbon route for synthesizing transportation fuels and value‐added chemicals. [ABSTRACT FROM AUTHOR]

Direct utilization of high-energy photons to drive chemical reactions presents a promising approach for the achievement of green reaction process. Herein, we developed a simple photochemical route that utilized 172 nm vacuum ultraviolet (VUV) photons as drivers for CO2 hydrogenation to CO and transformation of CH4 to H2 and C2H6. It was demonstrated that the reactions could proceed efficiently at catalyst-free and ambient conditions, and water could further promote the transformation of CH4. The reaction mechanism was proposed on the basis of control experiments. This study provides a green alternative to conventional catalytic processes for important reactions, i.e., CO2 hydrogenation or CH4 conversions triggered by high-energy photons under ambient conditions, which have promising potential in applications due to some obvious advantages. [ABSTRACT FROM AUTHOR]

Direct utilization of high-energy photons to drive chemical reactions presents a promising approach for the achievement of green reaction process. Herein, we developed a simple photochemical route that utilized 172 nm vacuum ultraviolet (VUV) photons as drivers for CO2 hydrogenation to CO and transformation of CH4 to H2 and C2H6. It was demonstrated that the reactions could proceed efficiently at catalyst-free and ambient conditions, and water could further promote the transformation of CH4. The reaction mechanism was proposed on the basis of control experiments. This study provides a green alternative to conventional catalytic processes for important reactions, i.e., CO2 hydrogenation or CH4 conversions triggered by high-energy photons under ambient conditions, which have promising potential in applications due to some obvious advantages. [ABSTRACT FROM AUTHOR]

Hydrogen (H2) has emerged as a clean and versatile energy carrier to power a carbon‐neutral economy for the post‐fossil era. Hydrogen generation from low‐cost and renewable biomass by virtually inexhaustible solar energy presents an innovative strategy to process organic solid waste, combat the energy crisis, and achieve carbon neutrality. Herein, the progress and breakthroughs in solar‐powered H2 production from biomass are reviewed. The basic principles of solar‐driven H2 generation from biomass are first introduced for a better understanding of the reaction mechanism. Next, the merits and shortcomings of various semiconductors and cocatalysts are summarized, and the strategies for addressing the related issues are also elaborated. Then, various bio‐based feedstocks for solar‐driven H2 production are reviewed with an emphasis on the effect of photocatalysts and catalytic systems on performance. Of note, the concurrent generation of value‐added chemicals from biomass reforming is emphasized as well. Meanwhile, the emerging photo‐thermal coupling strategy that shows a grand prospect for maximally utilizing the entire solar energy spectrum is also discussed. Further, the direct utilization of hydrogen from biomass as a green reductant for producing value‐added chemicals via organic reactions is also highlighted. Finally, the challenges and perspectives of photoreforming biomass toward hydrogen are envisioned. [ABSTRACT FROM AUTHOR]

Opportunity for future green hydrogen development in Nepal comes with end- use infrastructural challenges. The heavy reliance of industries on fossil fuels (63.4%) despite the abundance of hydroelectricity poses an additional challenge to the green transition of Nepal. The presented work aims to study the possibility of storing and utilizing spilled hydroelectricity due to runoff rivers as a compatible alternative to imported petroleum fuels. This is achieved by converting green hydrogen from water electrolysis and carbon dioxide from carbon capture of hard-to-abate industries into synthetic methane for heating applications via the Sabatier process. An economy-of-scale study was conducted to identify the optimal scale for the reference case (Industries in Makwanpur District Nepal) for establishing the Synthetic Natural Gas (SNG) production industry. The techno- economic assessment was carried out for pilot scale and reference scale production unit individually. Uncertainty and sensitivity analyses were performed to study the project profitability and the sensitivity of the parameters influencing the feasibility of the production plant. The reference scale for the production of Synthetic Natural Gas was determined to be 40 Tons Per Day (TPD), with a total capital investment of around 72.15 Million USD. Electricity was identified as the most sensitive parameter affecting the levelized cost of production (LCOP). The 40 TPD plant was found to be price competitive to LPG when electricity price is subsidized below 3.55 NPR/unit (2.7 c/unit) from 12 NPR/unit (9.2 c/unit). In the case of the 2 TPD plant, for it to be profitable, the price of electricity must be subsidized to well below 2 NPR/kWh. The study concludes that the possibility of SNG production in Nepal is profitable and price-competitive at large scales and at the same time limited by the low round efficiency due to conversion losses. Additionally, it was observed that highly favorable conditions driven by government policies would be required for the pilot-scale SNG project to be feasible. [ABSTRACT FROM AUTHOR]

Light‐driven hydrogen production from biomass derivatives offers a path towards carbon neutrality. It is often however operated with the limitations of sluggish kinetics and severe coking. Herein, a disruptive air‐promoted strategy is explored for efficient and durable light‐driven hydrogen production from ethanol over a core/shell Cr2O3@GaN nanoarchitecture. The correlative computational and experimental investigations show ethanol is energetically favorable to be adsorbed on the Cr2O3@GaN interface, followed by dehydrogenation toward acetaldehyde and protons by photoexcited holes. The released protons are then consumed for H2 evolution by photogenerated electrons. Afterward, O2 can be evolved into active oxygen species and promote the deprotonation and C−C cleavage of the key C2 intermediate, thus significantly lowering the reaction energy barrier of hydrogen evolution and removing the carbon residual with inhibited overoxidation. Consequently, hydrogen is produced at a high rate of 76.9 mole H2 per gram Cr2O3@GaN per hour by only feeding ethanol, air, and light, leading to the achievement of a turnover number of 266,943,000 mole H2 per mole Cr2O3 over a long‐term operation of 180 hours. Notably, an unprecedented light‐to‐hydrogen efficiency of 17.6 % is achieved under concentrated light illumination. The simultaneous generation of aldehyde from ethanol dehydrogenation enables the process more economically promising. [ABSTRACT FROM AUTHOR]

Upcycling of CO2 into fuels by virtually unlimited solar energy provides an ultimate solution for addressing the substantial challenges of energy crisis and climate change. In this work, we report an efficient nanostructured Ru/MnOx catalyst composed of well-defined Ru/MnO/Mn3O4 for photo-thermal catalytic CO2 hydrogenation to CH4, which is the result of a combination of external heating and irradiation. Remarkably, under relatively mild conditions of 200 °C, a considerable CH4 production rate of 166.7 mmol g−1 h−1 was achieved with a superior selectivity of 99.5% at CO2 conversion of 66.8%. The correlative spectroscopic and theoretical investigations suggest that the yield of CH4 is enhanced by coordinating photon energy with thermal energy to reduce the activation energy of reaction and promote formation of key intermediate COOH* species over the catalyst. This work opens up a new strategy for CO2 hydrogenation toward CH4. Reduction of CO2 with solar energy is an attractive route to new fuel sources. Here a nanostructured Ru/MnOx photo-thermal catalyst composed of well-defined Ru/MnO/Mn3O4 is reported for CO2 hydrogenation with high selectivity and a CH4 production rate at a mild temperature of 200 °C. [ABSTRACT FROM AUTHOR]

Photoelectrocatalytic (PEC) production of fuels and chemicals by using solar energy, water, and CO2 paves a promising avenue toward carbon neutrality. Over the past decades, for accelerating this process, a variety of photocathodes have been explored. Among them, the hybrid of GaN nanowires (NWs) and planar silicon has appeared as a disruptive platform for this grand topic, owing to their distinctive structural, optoelectronic, and catalytic properties. This review illustrates the most recent advances in GaN NWs/Si-based photocathodes for CO2 reduction reactions powered by simulated sunlight, beginning with a discussion of the critical requirements and fundamental challenges of PEC CO2 reduction. The characteristics of GaN NWs/Si are then discussed, showing its great potential in precisely controlling the behavior of photons, charges, and chemical species. As the focus of this review, the progress on the PEC CO2 reduction reactions toward different products over GaN NWs/Si-based photocathodes is highlighted. In the end, the challenges and prospects of GaN NWs/Si-based photocathodes for the practical synthesis of solar fuels and chemicals are proposed. [ABSTRACT FROM AUTHOR]