Leave No Photon Behind: Artificial Intelligence in Multiscale Physics of Photocatalyst and Photoreactor Design.

Although solar fuels photocatalysis offers the promise of converting carbon dioxide directly with sunlight as commercially scalable solutions have remained elusive over the past few decades, despite significant advancements in photocatalysis band-gap engineering and atomic site activity. The primary challenge lies not in the discovery of new catalyst materials, which are abundant, but in overcoming the bottlenecks related to material-photoreactor synergy. These factors include achieving photogeneration and charge-carrier recombination at reactive sites, utilizing high mass transfer efficiency supports, maximizing solar collection, and achieving uniform light distribution within a reactor. Addressing this multi-dimensional problem necessitates harnessing machine learning techniques to analyze real-world data from photoreactors and material properties. In this perspective, the challenges are outlined associated with each bottleneck factor, review relevant data analysis studies, and assess the requirements for developing a comprehensive solution that can unlock the full potential of solar fuels photocatalysis technology. Physics-informed machine learning (or Physics Neural Networks) may be the key to advancing this important area from disparate data towards optimal reactor solutions.

Visualizing the Birth and Monitoring the Life of a Bimetallic Methanation Catalyst.

Well-defined bimetallic heterogeneous catalysts are not only difficult to synthesize in a controlled manner, but their elemental distributions are also notoriously challenging to define. Knowledge of these distributions is required for both the as-synthesized catalyst and its activated form under reaction conditions, where various types of reconstruction can occur. Success in this endeavor requires observation of the active catalyst via in situ analytical methods. As a step toward this goal, we present a composite material composed of bimetallic nickel-ruthenium nanoparticles supported on a protonated zeolite (Ni-Ru/HZSM-5) and probe its evolution and function as a photoactive carbon dioxide methanation catalyst using in situ X-ray absorption spectroscopy (XAS). The working Ni-Ru/HZSM-5, as a selective and durable photothermal CO2 methanation catalyst, comprises a corona of Ru nanoparticles decorating a Ni nanoparticle core. The specific Ni-Ru interactions in the bimetallic particles were confirmed by in situ XAS, which reveals significant electron transfer from Ni to Ru. The light-harvesting Ni nanoparticle core and electron-accepting Ru nanoparticle corona serve as the CO2 and H2 dissociation centers, respectively. These Ni and Ru nanoparticles also promote synergistic photothermal and hydrogen atom transfer effects. Collectively, these effects enable an associative CO2 methanation reaction pathway while hindering coking and fostering high selectivity toward methane.

Wettability Engineering of Solar Methanol Synthesis.

Engineering the wettability of surfaces with hydrophobic organics has myriad applications in heterogeneous catalysis and the large-scale chemical industry; however, the mechanisms behind may surpass the proverbial hydrophobic kinetic benefits. Herein, the well-studied In2O3 methanol synthesis photocatalyst has been used as an archetype platform for a hydrophobic treatment to enhance its performance. With this strategy, the modified samples facilitated the tuning of a wide range of methanol production rates and selectivity, which were optimized at 1436 µmol gcat-1 h-1 and 61%, respectively. Based on in situ DRIFTS and temperature-programmed desorption-mass spectrometry, the surface-decorated alkylsilane coating on In2O3 not only kinetically enhanced the methanol synthesis by repelling the produced polar molecules but also donated surface active H to facilitate the subsequent hydrogenation reaction. Such a wettability design strategy seems to have universal applicability, judged by its success with other CO2 hydrogenation catalysts, including Fe2O3, CeO2, ZrO2, and Co3O4. Based on the discovered kinetic and mechanistic benefits, the enhanced hydrogenation ability enabled by hydrophobic alkyl groups unleashes the potential of the surface organic chemistry modification strategy for other important catalytic hydrogenation reactions.

Photochemical Acceleration of Ammonia Production by Pt1-Ptn-TiN Reduction and N2 Activation.

Stable metal nitrides (MN) are promising materials to fit the future "green" ammonia-hydrogen nexus. Either through catalysis or chemical looping, the reductive hydrogenation of MN to MN1-x is a necessary step to generate ammonia. However, encumbered by the formation of kinetically stable M-NH1─3 surface species, this reduction step remains challenging under mild conditions. Herein, we discovered that deleterious Ti-NH1─3 accumulation on TiN can be circumvented photochemically with supported single atoms and clusters of platinum (Pt1-Ptn) under N2-H2 conditions. The photochemistry of TiN selectively promoted Ti-NH formation, while Pt1-Ptn effectively transformed any formed Ti-NH into free ammonia. The generated ammonia was found to originate mainly from TiN reduction with a minor contribution from N2 activation. The knowledge accrued from this fundamental study could serve as a springboard for the development of MN materials for more efficient ammonia production to potentially disrupt the century-old fossil-powered Haber-Bosch process.

Solar Hydrocarbons: Single-Step, Atmospheric-Pressure Synthesis of C2 -C4 Alkanes and Alkenes from CO2.

Cobalt ferrite (CoFe2 O4 ) spinel has been found to produce C2 -C4 hydrocarbons in a single-step, ambient-pressure, photocatalytic hydrogenation of CO2 with a rate of 1.1 mmol g-1 h-1 , selectivity of 29.8 % and conversion yield of 12.9 %. On stream the CoFe2 O4 reconstructs to a CoFe-CoFe2 O4 alloy-spinel nanocomposite which facilitates the light-assisted transformation of CO2 to CO and hydrogenation of the CO to C2 -C4 hydrocarbons. Promising results obtained from a laboratory demonstrator bode well for the development of a solar hydrocarbon pilot refinery.

Supercharged CO2 Photothermal Catalytic Methanation: High Conversion, Rate, and Selectivity.

To overcome the thermodynamic and kinetic impediments of the Sabatier CO2 methanation reaction, the process must be operated under very high temperature and pressure conditions, to obtain an industrially viable conversion, rate, and selectivity. Herein, we report that these technologically relevant performance metrics have been achieved under much milder conditions using solar rather than thermal energy, where the methanation reaction is enabled by a novel nickel-boron nitride catalyst. In this regard, an in situ generated HOB⋅⋅⋅B surface frustrated Lewis's pair is considered responsible for the high Sabatier conversion 87.68 %, reaction rate 2.03 mol gNi -1 h-1 , and near 100 % selectivity, realized under ambient pressure conditions. This discovery bodes well for an opto-chemical engineering strategy aimed at the development and implementation of a sustainable 'Solar Sabatier' methanation process.

Engineered disorder in CO2 photocatalysis.

Light harvesting, separation of charge carriers, and surface reactions are three fundamental steps that are essential for an efficient photocatalyst. Here we show that these steps in the TiO2 can be boosted simultaneously by disorder engineering. A solid-state reduction reaction between sodium and TiO2 forms a core-shell c-TiO2@a-TiO2-x(OH)y heterostructure, comprised of HO-Ti-[O]-Ti surface frustrated Lewis pairs (SFLPs) embedded in an amorphous shell surrounding a crystalline core, which enables a new genre of chemical reactivity. Specifically, these SFLPs heterolytically dissociate dihydrogen at room temperature to form charge-balancing protonated hydroxyl groups and hydrides at unsaturated titanium surface sites, which display high reactivity towards CO2 reduction. This crystalline-amorphous heterostructure also boosts light absorption, charge carrier separation and transfer to SFLPs, while prolonged carrier lifetimes and photothermal heat generation further enhance reactivity. The collective results of this study motivate a general approach for catalytically generating sustainable chemicals and fuels through engineered disorder in heterogeneous CO2 photocatalysts.

Grave-to-cradle upcycling of Ni from electroplating wastewater to photothermal CO2 catalysis.

Treating hazardous waste Ni from the electroplating industry is mandated world-wide, is exceptionally expensive, and carries a very high CO2 footprint. Rather than regarding Ni as a disposable waste, the chemicals and petrochemicals industries could instead consider it a huge resource. In the work described herein, we present a strategy for upcycling waste Ni from electroplating wastewater into a photothermal catalyst for converting CO2 to CO. Specifically, magnetic nanoparticles encapsulated in amine functionalized porous SiO2, is demonstrated to efficiently scavenge Ni from electroplating wastewater for utilization in photothermal CO2 catalysis. The core-shell catalyst architecture produces CO at a rate of 1.9 mol·gNi-1·h-1 (44.1 mmol·gcat-1·h-1), a selectivity close to 100%, and notable long-term stability. This strategy of upcycling metal waste into functional, catalytic materials offers a multi-pronged approach for clean and renewable energy technologies.

New black indium oxide-tandem photothermal CO2-H2 methanol selective catalyst.

It has long been known that the thermal catalyst Cu/ZnO/Al2O3(CZA) can enable remarkable catalytic performance towards CO2 hydrogenation for the reverse water-gas shift (RWGS) and methanol synthesis reactions. However, owing to the direct competition between these reactions, high pressure and high hydrogen concentration (≥75%) are required to shift the thermodynamic equilibrium towards methanol synthesis. Herein, a new black indium oxide with photothermal catalytic activity is successfully prepared, and it facilitates a tandem synthesis of methanol at a low hydrogen concentration (50%) and ambient pressure by directly using by-product CO as feedstock. The methanol selectivities achieve 33.24% and 49.23% at low and high hydrogen concentrations, respectively.

Stable Cu Catalysts Supported by Two-dimensional SiO2 with Strong Metal-Support Interaction.

Cu-based catalysts exhibit excellent performance in hydrogenation reactions. However, the poor stability of Cu catalysts under high temperatures has restricted their practical applications. The preparation of stable Cu catalysts supported by SiO2 with strong metal-support interaction (SMSI) has thus aroused great interest due to the high abundance, low toxicity, feasible processability, and low cost of SiO2 . The challenge in the construction of such SMSI remains to be the inertness of SiO2 . Herein, a simple and scalable method is developed to prepare 2D silica (2DSiO2 ) supported Cu catalysts with SMSI by carefully manipulating the topological exfoliation of CaSi2 with CuCl2 and thereafter calcination. The prepared Cu-2DSiO2 catalysts with the unique encapsulated Cu nanoparticles exhibit excellent activity and long-term stability in high-temperature CO2 hydrogenation reactions. This feasible and low-cost solution for stabilizing Cu catalysts might shed light on their realistic applications.

Near-Perfect Absorbing Copper Metamaterial for Solar Fuel Generation.

Metamaterials are a new class of artificial materials that can achieve electromagnetic properties that do not occur naturally, and as such they can also be a new class of photocatalytic structures. We show that metal-based catalysts can achieve electromagnetic field amplification and broadband absorption by decoupling optical properties from the material composition as exemplified with a ZnO/Cu metamaterial surface comprising periodically arranged nanocubes. Through refractive index engineering close to the index of air, the metamaterial exhibits near-perfect 98% absorption. The combination of plasmonics and broadband absorption elevates the weak electric field intensities across the nonplasmonic absorption range. This feedback between optical excitation and plasmonic excitation dramatically enhances light-to-dark catalytic rates by up to a factor of 181 times, compared to a 3 times photoenhancement of ZnO/Cu nanoparticles or films, and with angular invariance. These results show that metamaterial catalysts can act as a singular light harvesting device that substantially enhances photocatalysis of important reactions.

Efficient CO2 electroreduction on facet-selective copper films with high conversion rate.

Tuning the facet exposure of Cu could promote the multi-carbon (C2+) products formation in electrocatalytic CO2 reduction. Here we report the design and realization of a dynamic deposition-etch-bombardment method for Cu(100) facets control without using capping agents and polymer binders. The synthesized Cu(100)-rich films lead to a high Faradaic efficiency of 86.5% and a full-cell electricity conversion efficiency of 36.5% towards C2+ products in a flow cell. By further scaling up the electrode into a 25 cm2 membrane electrode assembly system, the overall current can ramp up to 12 A while achieving a single-pass yield of 13.2% for C2+ products. An insight into the influence of Cu facets exposure on intermediates is provided by in situ spectroscopic methods supported by theoretical calculations. The collected information will enable the precise design of CO2 reduction reactions to obtain desired products, a step towards future industrial CO2 refineries.

Construction of New Active Sites: Cu Substitution Enabled Surface Frustrated Lewis Pairs over Calcium Hydroxyapatite for CO2 Hydrogenation.

Calcium hydroxyphosphate, Ca10 (PO4 )6 (OH)2 , is commonly known as hydroxyapatite (HAP). The acidic calcium and basic phosphate/hydroxide sites in HAP can be modified via isomorphous substitution of calcium and/or hydroxide ions to enable a cornucopia of catalyzed reactions. Herein, isomorphic substitution of Ca2+ ions by Cu2+ ions especially at very low levels of exchange created new analogs of molecular surface frustrated Lewis pairs (SFLPs) in Cux Ca10-x (PO4 )6 (OH)2 , thereby boosting its performance metrics in heterogeneous CO2 photocatalytic hydrogenation. In situ Fourier transform infrared spectroscopy characterization and density functional theory calculations provided fundamental insights into the catalytically active SFLPs defined as proximal Lewis acidic Cu2+ and Lewis basic OH- . The photocatalytic pathway proceeds through a formate reaction intermediate, which is generated by the reaction of CO2 with heterolytically dissociated H2 on the SFLPs. Given the wealth of information thus uncovered, it is highly likely that this work will spur the further development of similar classes of materials, leading to the advancement and, ultimately, large-scale application of photocatalytic CO2 reduction technologies.

CO2 Footprint of Thermal Versus Photothermal CO2 Catalysis.

Transformation of CO2 into value-added products via photothermal catalysis has become an increasingly popular route to help ameliorate the energy and environmental crisis derived from the continuing use of fossil fuels, as it can integrate light into well-established thermocatalysis processes. The question however remains whether negative CO2 emission could be achieved through photothermal catalytic reactions performed in facilities driven by electricity mainly derived from fossil energy. Herein, we propose universal equations that describe net CO2 emissions generated from operating thermocatalysis and photothermal reverse water-gas shift (RWGS) and Sabatier processes for batch and flow reactors. With these reactions as archetype model systems, the factors that will determine the final amount of effluent CO2 can be determined. The results of this study could provide useful guidelines for the future development of photothermal catalytic systems for CO2 reduction.

Niobium and Titanium Carbides (MXenes) as Superior Photothermal Supports for CO2 Photocatalysis.

The conversion of CO2 into fuels and feedstock chemicals via photothermal catalysis holds promise for efficient solar energy utilization to tackle the global energy shortage and climate change. Despite recent advances, it is of emerging interest to explore promising materials with excellent photothermal properties to boost the performance of photothermal CO2 catalysis. Here, we report the discovery of MXene materials as superior photothermal supports for metal nanoparticles. As a proof-of-concept study, we demonstrate that Nb2C and Ti3C2, two typical MXene materials, can enhance the photothermal effect and thus boost the photothermal catalytic activity of Ni nanoparticles. A record CO2 conversion rate of 8.50 mol·gNi-1·h-1 is achieved for Nb2C-nanosheet-supported Ni nanoparticles under intense illumination. Our study bridges the gap between photothermal MXene materials and photothermal CO2 catalysis toward more efficient solar-to-chemical energy conversions and stimulates the interest in MXene-supported metal nanoparticles for other heterogeneous catalytic reactions, particularly driven by sunlight.

The nature of active sites for carbon dioxide electroreduction over oxide-derived copper catalysts.

The active sites for CO2 electroreduction (CO2R) to multi-carbon (C2+) products over oxide-derived copper (OD-Cu) catalysts are under long-term intense debate. This paper describes the atomic structure motifs for product-specific active sites on OD-Cu catalysts in CO2R. Herein, we describe realistic OD-Cu surface models by simulating the oxide-derived process via the molecular dynamic simulation with neural network (NN) potential. After the analysis of over 150 surface sites through NN potential based high-throughput testing, coupled with density functional theory calculations, three square-like sites for C-C coupling are identified. Among them, Σ3 grain boundary like planar-square sites and convex-square sites are responsible for ethylene production while step-square sites, i.e. n(111) × (100), favor alcohols generation, due to the geometric effect for stabilizing acetaldehyde intermediates and destabilizing Cu-O interactions, which are quantitatively demonstrated by combined theoretical and experimental results. This finding provides fundamental insights into the origin of activity and selectivity over Cu-based catalysts and illustrates the value of our research framework in identifying active sites for complex heterogeneous catalysts.

Enhanced CO2 Photocatalysis by Indium Oxide Hydroxide Supported on TiN@TiO2 Nanotubes.

Herein is developed a ternary heterostructured catalyst, based on a periodic array of 1D TiN nanotubes, with a TiO2 nanoparticulate intermediate layer and a In2O3-x(OH)y nanoparticulate shell for improved performance in the photocatalytic reverse water gas shift reaction. It is demonstrated that the ordering of the three components in the heterostructure sensitively determine its activity in CO2 photocatalysis. Specifically, TiN nanotubes not only provide a photothermal driving force for the photocatalytic reaction, owing to their strong optical absorption properties, but they also serve as a crucial scaffold for minimizing the required quantity of In2O3-x(OH)y nanoparticles, leading to an enhanced CO production rate. Simultaneously, the TiO2 nanoparticle layer supplies photogenerated electrons and holes that are transferred to active sites on In2O3-x(OH)y nanoparticles and participate in the reactions occurring at the catalyst surface.

Bismuth atom tailoring of indium oxide surface frustrated Lewis pairs boosts heterogeneous CO2 photocatalytic hydrogenation.

The surface frustrated Lewis pairs (SFLPs) on defect-laden metal oxides provide catalytic sites to activate H2 and CO2 molecules and enable efficient gas-phase CO2 photocatalysis. Lattice engineering of metal oxides provides a useful strategy to tailor the reactivity of SFLPs. Herein, a one-step solvothermal synthesis is developed that enables isomorphic replacement of Lewis acidic site In3+ ions in In2O3 by single-site Bi3+ ions, thereby enhancing the propensity to activate CO2 molecules. The so-formed BixIn2-xO3 materials prove to be three orders of magnitude more photoactive for the reverse water gas shift reaction than In2O3 itself, while also exhibiting notable photoactivity towards methanol production. The increased solar absorption efficiency and efficient charge-separation and transfer of BixIn2-xO3 also contribute to the improved photocatalytic performance. These traits exemplify the opportunities that exist for atom-scale engineering in heterogeneous CO2 photocatalysis, another step towards the vision of the solar CO2 refinery.

Plasmonic Titanium Nitride Facilitates Indium Oxide CO2 Photocatalysis.

Nanoscale titanium nitride TiN is a metallic material that can effectively harvest sunlight over a broad spectral range and produce high local temperatures via the photothermal effect. Nanoscale indium oxide-hydroxide, In2 O3- x (OH)y , is a semiconducting material capable of photocatalyzing the hydrogenation of gaseous CO2 ; however, its wide electronic bandgap limits its absorption of photons to the ultraviolet region of the solar spectrum. Herein, the benefits of both nanomaterials in a ternary heterostructure: TiN@TiO2 @In2 O3- x (OH)y are combined. This heterostructured material synergistically couples the metallic TiN and semiconducting In2 O3- x (OH)y phases via an interfacial semiconducting TiO2 layer, allowing it to drive the light-assisted reverse water gas shift reaction at a conversion rate greatly surpassing that of its individual components or any binary combinations thereof.

Electrolyte-Phobic Surface for the Next-Generation Nanostructured Battery Electrodes.

Nanostructured electrodes are among the most important candidates for high-capacity battery chemistry. However, the high surface area they possess causes serious issues. First, it would decrease the Coulombic efficiencies. Second, they have significant intakes of liquid electrolytes, which reduce the energy density and increase the battery cost. Third, solid-electrolyte interphase growth is accelerated, affecting the cycling stability. Therefore, the interphase chemistry regarding electrolyte contact is crucial, which was rarely studied. Here, we present a completely new strategy of limiting effective surface area by introducing an "electrolyte-phobic surface". Using this method, the electrolyte intake was limited. The initial Coulombic efficiencies were increased up to ∼88%, compared to ∼60% of the control. The electrolyte-phobic layer of Si particles is also compatible with the binder, stabilizing the electrode for long-term cycling. This study advances the understanding of interphase chemistry, and the introduction of the universal concept of electrolyte-phobicity benefits the next-generation battery designs.