Solar-to-hydrogen efficiency of more than 9% in photocatalytic water splitting.

Production of hydrogen fuel from sunlight and water, two of the most abundant natural resources on Earth, offers one of the most promising pathways for carbon neutrality1-3. Some solar hydrogen production approaches, for example, photoelectrochemical water splitting, often require corrosive electrolyte, limiting their performance stability and environmental sustainability1,3. Alternatively, clean hydrogen can be produced directly from sunlight and water by photocatalytic water splitting2,4,5. The solar-to-hydrogen (STH) efficiency of photocatalytic water splitting, however, has remained very low. Here we have developed a strategy to achieve a high STH efficiency of 9.2 per cent using pure water, concentrated solar light and an indium gallium nitride photocatalyst. The success of this strategy originates from the synergistic effects of promoting forward hydrogen-oxygen evolution and inhibiting the reverse hydrogen-oxygen recombination by operating at an optimal reaction temperature (about 70 degrees Celsius), which can be directly achieved by harvesting the previously wasted infrared light in sunlight. Moreover, this temperature-dependent strategy also leads to an STH efficiency of about 7 per cent from widely available tap water and sea water and an STH efficiency of 6.2 per cent in a large-scale photocatalytic water-splitting system with a natural solar light capacity of 257 watts. Our study offers a practical approach to produce hydrogen fuel efficiently from natural solar light and water, overcoming the efficiency bottleneck of solar hydrogen production.

Tunable green syngas generation from CO2 and H2O with sunlight as the only energy input.

The carbon-neutral synthesis of syngas from CO2 and H2O powered by solar energy holds grand promise for solving critical issues such as global warming and the energy crisis. Here we report photochemical reduction of CO2 with H2O into syngas using core/shell Au@Cr2O3 dual cocatalyst-decorated multistacked InGaN/GaN nanowires (NWs) with sunlight as the only energy input. First-principle density functional theory calculations revealed that Au and Cr2O3 are synergetic in deforming the linear CO2 molecule to a bent state with an O-C-O angle of 116.5°, thus significantly reducing the energy barrier of CO2RR compared with that over a single component of Au or Cr2O3. Hydrogen evolution reaction was promoted by the same cocatalyst simultaneously. By combining the cooperative catalytic properties of Au@Cr2O3 with the distinguished optoelectronic virtues of the multistacked InGaN NW semiconductor, the developed photocatalyst demonstrated high syngas activity of 1.08 mol/gcat/h with widely tunable H2/CO ratios between 1.6 and 9.2 under concentrated solar light illumination. Nearly stoichiometric oxygen was evolved from water splitting at a rate of 0.57 mol/gcat/h, and isotopic testing confirmed that syngas originated from CO2RR. The solar-to-syngas energy efficiency approached 0.89% during overall CO2 reduction coupled with water splitting. The work paves a way for carbon-neutral synthesis of syngas with the sole inputs of CO2, H2O, and solar light.

Chirality Engineering of Nanostructured Copper Oxide for Enhancing Oxygen Evolution from Water Electrolysis.

The exploration of a new conceptual strategy for improving the oxygen evolution reaction (OER) of earth-abundant electrocatalysts is critical. In this study, chiral copper oxide nanoflower is explored by a self-assembly method. The characterization suggests the chiral structure originates from the crystal plane-level helical stack of the secondary nanosheets. Of note, the assembly illustrates a record-high degree of spin polarization of 96%, indicating the ideal alignment of electron spin. Moreover, density function theory calculations show the chiral structure reducing the reaction energy barrier (REB) while switching the potential-determining step from *O→*OOH to *OH→*O. Together with the enhanced electrochemical active surface area and accelerated charge transfer, the production of ground-state triplet O2 is improved via a spin-forbidden route that involves the singlet H2O/OH•. Consequently, the chiral nanoflower shows a overpotential of 308 mV at 10 mA cm-2 and a Tafel slope of 93.5 mV dec-1, which is even superior to the commercial RuO2 (310 mV, 101 mV dec-1). This study presents a new strategy for improving the OER activity by simultaneously enhancing electronic properties and lowering the REB of an non-noble electrocatalyst via chirality engineering.

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.

Green Syngas Production from Natural Lignin, Sunlight, and Water over Pt-Decorated InGaN Nanowires.

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.

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. By assembling with InGaN nanowires on a Si wafer, the as-designed dual FeMn cocatalyst 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. By correlating exploration experiments, the critical role of the dual FeMn cocatalyst in the evolving mechanism of lignin and water toward syngas is disclosed at the atomic level. It is discovered 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. This work demonstrates a new and earth-abundant bifunctional cocatalyst for utilizing various substituents of lignin to produce syngas powered by sunlight beyond fossil fuels.

Air-Promoted Light-Driven Hydrogen Production from Bioethanol over Core/Shell Cr2O3@GaN Nanoarchitecture.

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.

Highly efficient binary copper-iron catalyst for photoelectrochemical carbon dioxide reduction toward methane.

A rational design of an electrocatalyst presents a promising avenue for solar fuels synthesis from carbon dioxide (CO2) fixation but is extremely challenging. Herein, we use density functional theory calculations to study an inexpensive binary copper-iron catalyst for photoelectrochemical CO2 reduction toward methane. The calculations of reaction energetics suggest that Cu and Fe in the binary system can work in synergy to significantly deform the linear configuration of CO2 and reduce the high energy barrier by stabilizing the reaction intermediates, thus spontaneously favoring CO2 activation and conversion for methane synthesis. Experimentally, the designed CuFe catalyst exhibits a high current density of -38.3 mA⋅cm-2 using industry-ready silicon photoelectrodes with an impressive methane Faradaic efficiency of up to 51%, leading to a distinct turnover frequency of 2,176 h-1 under air mass 1.5 global (AM 1.5G) one-sun illumination.

Photoelectrochemical CO2 Reduction into Syngas with the Metal/Oxide Interface.

Photoelectrochemical (PEC) reduction of CO2 with H2O not only provides an opportunity for reducing net CO2 emissions but also produces value-added chemical feedstocks and fuels. Syngas, a mixture of CO and H2, is a key feedstock for the production of methanol and other commodity hydrocarbons in industry. However, it is challenging to achieve efficient and stable PEC CO2 reduction into syngas with controlled composition owing to the difficulties associated with the chemical inertness of CO2 and complex reaction network of CO2 conversion. Herein, by employing a metal/oxide interface to spontaneously activate CO2 molecule and stabilize the key reaction intermediates, we report a benchmarking solar-to-syngas efficiency of 0.87% and a high turnover number of 24 800, as well as a desirable high stability of 10 h. Moreover, the CO/H2 ratios in the composition can be tuned in a wide range between 4:1 and 1:6 with a total unity Faradaic efficiency. On the basis of experimental measurements and theoretical calculations, we present that the metal/oxide interface provides multifunctional catalytic sites with complementary chemical properties for CO2 activation and conversion, leading to a unique pathway that is inaccessible with the individual components. The present approach opens new opportunities to rationally develop high-performance PEC systems for selective CO2 reduction into valuable carbon-based chemicals and fuels.

Porous Zirconium-Phytic Acid Hybrid: a Highly Efficient Catalyst for Meerwein-Ponndorf-Verley Reductions.

The utilization of compounds from natural sources to prepare functional materials is of great importance. Herein, we describe for the first time the preparation of organic-inorganic hybrid catalysts by using natural phytic acid as building block. Zirconium phosphonate (Zr-PhyA) was synthesized by reaction of phytic acid and ZrCl4 and was obtained as a mesoporous material with pore sizes centered around 8.5 nm. Zr-PhyA was used to catalyze the mild and selective Meerwein-Ponndorf-Verley (MPV) reduction of various carbonyl compounds, e.g., of levulinic acid and its esters into γ-valerolactone. Further studies indicated that both Zr and phosphate groups contribute significantly to the excellent performance of Zr-PhyA.

Solar-Driven Biomass Reforming for Hydrogen Generation: Principles, Advances, and Challenges.

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.

Paclitaxel mediates the PI3K/AKT/mTOR pathway to reduce proliferation of FLT3­ITD+ AML cells and promote apoptosis.

Acute myeloid leukemia (AML) with internal tandem duplication (ITD) mutations in the FLT3 tyrosine kinase tend to have a poor prognosis. FLT3-ITD can promote the progress of AML by activating the PI3K/AKT/mTOR pathway. Paclitaxel (PTX) is a natural anticancer drug that has been widely used in chemotherapy for multiple malignancies. The present study used the CCK-8 assay, flow cytometry, PCR and western blotting to explore the anti-leukemia effect and possible mechanisms of PTX on MV4-11 cells with the FLT3-ITD mutation and the underlying mechanism. As a result, it was found that PTX could inhibit proliferation of MV4-11 cells and promoted apoptosis by inhibiting the PI3K/AKT/mTOR pathway.

Photo-thermal coupling to enhance CO2 hydrogenation toward CH4 over Ru/MnO/Mn3O4.

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.

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.

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.

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.

Oxynitrides enabled photoelectrochemical water splitting with over 3,000 hrs stable operation in practical two-electrode configuration.

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.

Photocatalytic Cleavage of C(sp3 )-N Bond in Trialkylamines to Dialkylamines and Olefins.

Development of a new and green strategy for C(sp3 )-N bond cleavage is very interesting. Herein, photocatalytic cleavage of the C(sp3 )-N bond of trialkylamines was achieved, with concurrent formation of dialkylamines and olefins. It was found that a rationally designed 2D-Bi2 WO6 @1D-LaPO4 heterostructure was very efficient for the reaction due to its high light collection efficiency and unique catalytic properties. The strategy could be used for different trialkylamines, including triethylamine, tri-n-propylamine, and ethyl-di-isopropylamine. The mechanistic investigation indicated that the catalyst with heterostructure was not only favorable for charge carrier separation but also rendered excited electrons with high reduction capacity. This work opens a way for C(sp3 )-N bond cleavage of trialkylamines.

Selective photocatalytic aerobic oxidation of methane into carbon monoxide over Ag/AgCl@SiO2.

Design of active catalysts for chemical utilization of methane under mild conditions is of great importance, but remains a challenging task. Here, we prepared a Ag/AgCl with SiO2 coating (Ag/AgCl@SiO2) photocatalyst for methane oxidation to carbon monoxide. High carbon monoxide production (2.3 µmol h-1) and high selectivity (73%) were achieved. SiO2 plays a key role in the superior performance by increasing the lifetime of the photogenerated charge carriers. Based on a set of semi in situ infrared spectroscopy, electron paramagnetic resonance, and electronic property characterization studies, it is revealed that CH4 is effectively and selectively oxidized to CO by the in situ formation of singlet 1O2 via the key intermediate of COOH*. Further study showed that the Ag/AgCl@SiO2 catalyst could also drive valuable conversion using real sunlight under ambient conditions. As far we know, this is the first work on the application of SiO2 modified Ag/AgCl in the methane oxidation reaction.