Oxynitride-surface engineering of rhodium-decorated gallium nitride for efficient thermocatalytic hydrogenation of carbon dioxide to carbon monoxide

Unlocking Methane Generation via Photo-Thermal-Coupled CO2 Hydrogenation by Integrating FeNiCrMnCo Multicomponent Alloy with GaN Nanowires

The exploration of a noble-metal-free photo-thermal-coupled catalytic architecture plays a vital role in solar-driven conversion of carbon dioxide (CO2) into high-value fuels and chemicals. In this study, FeNiCrMnCo multicomponent alloy (MCA) is integrated with GaN nanowires (NW's) for photo-thermal-coupled catalytic CO2 methanation. The MCA/GaN NW's nanohybrid demonstrates a considerable methane production rate of 199 mmol∙g-1∙h-1 with an impressive selectivity of 93% under white light irradiation of 3 W∙cm-2 at 290 °C by external heating. The turnover number approaches 20,160 mole CH4 per mole of MCA over a continuous operation period of 120 h, showcasing remarkable stability. Mechanistic investigations reveal that the unique MCA provides a flexible platform for tailoring the electronic and catalytic properties to optimize the adsorption and activation of CO₂ and H₂, thus leading to efficient and selective CO₂ methanation. This study presents an industry-friendly architecture for photo-thermal-coupled CO2 hydrogenation into high-value fuels and chemicals by coupling a noble-metal-free multicomponent alloy with GaN NWs, paving the way for advancements in sustainable energy conversion through CO2 utilization.

An integrated photocatalytic redox architecture for simultaneous overall conversion of CO2 and H2O toward CH4 and H2O2

Solar-driven overall conversion of CO2 and H2O into fuels and chemicals shows an ultimate strategy for carbon neutrality yet remains a huge challenge. Herein, an integrated photocatalytic redox architecture of Zn NPs/GaN Nanowires (NWs)/Si is explored for light-driven overall conversion of CO2 and H2O into CH4 and H2O2 simultaneously without any external sacrificial agents and additives. The as-designed architecture affords a benchmark CH4 activity of 189 mmol gcat-1 h-1 with a high selectivity of 93.6%, in the synchronized formation of H2O2 at a considerable rate of 25 m g-1 h-1. Moreover, a considerable turnover number of 27,280 mol CH4 per mol Zn was achieved over a long-term operation of 80 h. By operando spectroscopic characterizations, isotope experiments, and density functional theory calculations, it is unraveled that Zn sites are synergetic with GaN to drive CO2-to-CH4 conversion with a lowered energy barrier of 0.27 eV while inhibiting hydrogen evolution reaction with a relatively high energy barrier of 0.93 eV. Notably, owing to the unique surface properties of GaN, water is split into *OH and *H, followed by the formation of H2O2 because of the alleviated adsorption strength of *OH by Zn NPs. Together, the hierarchical architecture enables the achievement of high activity and high selectivity of CH4 from CO2 reduction in distilled water along with the generation of H2O2. This work provides an integrated photocatalytic redox architecture for the synchronized production of CH4 and H2O2 with the only inputs of CO2, distilled water, and light.

Surface-hydrogenated CrMnOx coupled with GaN nanowires for light-driven bioethanol dehydration to ethylene

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.

Binary Iron-Manganese Cocatalyst for Simultaneous Activation of C-C and C-O Bonds to Maximally Utilize Lignin for Syngas Generation over InGaN

Solar-powered lignin reforming offers a carbon-neutral route for syngas production. This study explores a dual non-precious iron-manganese cocatalyst to simultaneously activate both C-C and C-O bonds for maximizing the utilization of various substituents of native lignin to yield syngas. The cocatalyst, integrated with InGaN nanowires on a Si wafer, affords a measurable syngas evolution rate of 42.4 mol gcat -1 h-1 from native lignin in distilled water with a high selectivity of 93 % and tunable H2/CO ratios under concentrated light, leading to a considerable light-to-fuel efficiency of 11.8 %. The high FeMn atom efficiency arising from the 1-dimensional nanostructure of InGaN enables the achievement of a high turnover frequency (TOF) of 220896 mol syngas per mol FeMn per hour. Combined experimental and theoretical investigations reveal that the synergetic iron-manganese cocatalyst supported by InGaN nanowires enables simultaneous activation of C-C and C-O bonds with comparable minimized dissociation energies, thus promising to maximally utilize different substituents of -OCH3, and -CH2CH2CH3 in lignin for syngas production. Moreover, the dual Fe-Mn cocatalyst demonstrates a most energetically favorable route for the consecutive release of hydrogen from •CH3 and •OH by the oxidative holes while inhibiting the reversion of hydrogen and hydroxyl into water.

Utilizing full-spectrum sunlight for ammonia decomposition to hydrogen over GaN nanowires-supported Ru nanoparticles on silicon

Photo-thermal-coupling ammonia decomposition presents a promising strategy for utilizing the full-spectrum to address the H2 storage and transportation issues. Herein, we exhibit a photo-thermal-catalytic architecture by assembling gallium nitride nanowires-supported ruthenium nanoparticles on a silicon for extracting hydrogen from ammonia aqueous solution in a batch reactor with only sunlight input. The photoexcited charge carriers make a predomination contribution on H2 activity with the assistance of the photothermal effect. Upon concentrated light illumination, the architecture significantly reduces the activation energy barrier from 1.08 to 0.22 eV. As a result, a high turnover number of 3,400,750 is reported during 400 h of continuous light illumination, and the H2 activity per hour  is nearly 1000 times higher than that under the pure thermo-catalytic conditions. The reaction mechanism is extensively studied by coordinating experiments, spectroscopic characterizations, and density functional theory calculation. Outdoor tests validate the viability of such a multifunctional architecture for ammonia decomposition toward H2 under natural sunlight.

An Active and Robust Catalytic Architecture of NiCo/GaN Nanowires for Light-Driven Hydrogen Production from Methanol

On-site hydrogen production from liquid organic hydrogen carriers e.g., methanol provides an emerging strategy for the safe storage and transportation of hydrogen. Herein, a catalytic architecture consisting of nickel-cobalt nanoclusters dispersed on gallium nitride nanowires supported by silicon for light-driven hydrogen production from methanol is reported. By correlative microscopic, spectroscopic characterizations, and density functional theory calculations, it is revealed that NiCo nanoclusters work in synergy with GaN nanowires to enable the achievement of a significantly reduced activation energy of methanol dehydrogenation by switching the potential-limiting step from *CHO → *CO to *CH3O → *CH2O. In combination with the marked photothermal effect, a high hydrogen rate of 5.62 mol·gcat-1·h-1 with a prominent turnover frequency of 43,460 h-1 is achieved at 5 Wcm-2 without additional energy input. Remarkably, the synergy between Co and Ni, in combination with the unique surface of GaN, renders the architecture with outstanding resistance to sintering and coking. The architecture thereby exhibits a high turnover number of >16,310,000 over 600 h. Outdoor testing validates the viability of the architecture for active and robust hydrogen evolution under natural concentrated sunlight. Overall, this work presents a promising architecture for on-site hydrogen production from CH3OH by virtually unlimited solar energy.

Rh/InGaN1-xOx nanoarchitecture for light-driven methane reforming with carbon dioxide toward syngas

Light-driven dry reforming of methane toward syngas presents a proper solution for alleviating climate change and for the sustainable supply of transportation fuels and chemicals. Herein, Rh/InGaN1-xOx nanowires supported by silicon wafer are explored as an ideal platform for loading Rh nanoparticles, thus assembling a new nanoarchitecture for this grand topic. In combination with the remarkable photo-thermal synergy, the O atoms in Rh/InGaN1-xOx can significantly lower the apparent activation energy of dry reforming of methane from 2.96 eV downward to 1.70 eV. The as-designed Rh/InGaN1-xOx NWs nanoarchitecture thus demonstrates a measurable syngas evolution rate of 180.9 mmol gcat-1 h-1 with a marked selectivity of 96.3% under concentrated light illumination of 6 W cm-2. What is more, a high turnover number (TON) of 4182 mol syngas per mole Rh has been realized after six reuse cycles without obvious activity degradation. The correlative 18O isotope labeling experiments, in-situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) and in-situ diffuse reflectance Fourier transform infrared spectroscopy characterizations, as well as density functional theory calculations reveal that under light illumination, Rh/InGaN1-xOx NWs facilitate releasing *CH3 and H+ from CH4 by holes, followed by H2 evolution from H+ reduction with electrons. Subsequently, the O atoms in Rh/InGaN1-xOx can directly participate in CO generation by reacting with the *C species from CH4 dehydrogenation and contributes to the coke elimination, in concurrent formation of O vacancies. The resultant O vacancies are then replenished by CO2, showing an ideal chemical loop. This work presents a green strategy for syngas production via light-driven dry reforming of methane.

Photo-thermal synergistic CO2 hydrogenation towards CO over PtRh bimetal-decorated GaN nanowires/Si

Photo-thermal-synergistic hydrogenation is a promising strategy for upcycling carbon dioxide into fuels and chemicals by maximally utilizing full-spectrum solar energy. Herein, by immobilizing Pt-Rh bimetal onto a well-developed GaN NWs/Si platform, CO2 was photo-thermo-catalytically hydrogenated towards CO under concentrated light illumination without extra energies. The as-designed architecture demonstrates a considerable CO evolution rate of 11.7 mol gGaN-1 h-1 with a high selectivity of 98.5% under concentrated light illumination of 5.3 W cm-2, leading to a benchmark turnover frequency of 26 486 mol CO per mol PtRh per hour. It is nearly 2-3 orders of magnitude higher than that of pure thermal catalysis under the same temperature by external heating without light. Control experiments, various spectroscopic characterization methods, and density functional theory calculations are correlatively conducted to reveal the origin of the remarkable performance as well as the photo-thermal enhanced mechanism. It is found that the recombination of photogenerated electron-hole pairs is dramatically inhibited under high temperatures arising from the photothermal effect. More critically, the synergy between photogenerated carriers arising from ultraviolet light and photoinduced heat arising from visible- and infrared light enables a sharp reduction of the apparent activation barrier of CO2 hydrogenation from 2.09 downward to 1.18 eV. The evolution pathway of CO2 hydrogenation towards CO is also disclosed at the molecular level. Furthermore, compared to monometallic Pt, the introduction of Rh further reduces the desorption energy barrier of *CO by optimizing the electronic properties of Pt, thus enabling the achievement of excellent activity and selectivity. This work provides new insights into CO2 hydrogenation by maximally utilizing full-spectrum sunlight via photo-thermal synergy.

A semiconducting hybrid of RhOx/GaN@InGaN for simultaneous activation of methane and water toward syngas by photocatalysis

Prior to the eventual arrival of carbon neutrality, solar-driven syngas production from methane steam reforming presents a promising approach to produce transportation fuels and chemicals. Simultaneous activation of the two reactants, i.e. methane and water, with notable geometric and polar discrepancy is at the crux of this important subject yet greatly challenging. This work explores an exceptional semiconducting hybrid of RhOx/GaN@InGaN nanowires for overcoming this critical challenge to achieve efficient syngas generation from methane steam reforming by photocatalysis. By coordinating density functional theoretical calculations and microscopic characterizations, with in situ spectroscopic measurements, it is found that the multifunctional RhOx/GaN interface is effective for simultaneously activating both CH4 and H2O by stretching the C-H and O-H bonds because of its unique Lewis acid/base attribute. With the aid of energetic charge carriers, the stretched C-H and O-H bonds of reactants are favorably cleaved, resulting in the key intermediates, i.e. *CH3, *OH, and *H, to sit on Rh sites, Rh sites, and N sites, respectively. Syngas is subsequently produced via energetically favored pathway without additional energy inputs except for light. As a result, a benchmarking syngas formation rate of 8.1 mol·gcat-1·h-1 is achieved with varied H2/CO ratios from 2.4 to 0.8 under concentrated light illumination of 6.3 W·cm-2, enabling the achievement of a superior turnover number of 10,493 mol syngas per mol Rh species over 300 min of long-term operation. This work presents a promising strategy for green syngas production from methane steam reforming by utilizing unlimited solar energy.