High-Efficiency "Working-in-Tandem" Nitrogen Photofixation Achieved by Assembling Plasmonic Gold Nanocrystals on Ultrathin Titania Nanosheets

Free-Standing Nanoarrays with Energetic Electrons and Active Sites for Efficient Plasmon-Driven Ammonia Synthesis

Direct ammonia (NH₃ ) synthesis from water and atmospheric nitrogen using sunlight provides an energy-sustainable and carbon-neutral alternative to the Haber-Bosch process. However, the development of such a route with high performance is impeded by the lack of effective charge transfer and abundant active sites to initiate the nitrogen reduction reaction (NRR). Here, the authors report efficient plasmon-induced photoelectrochemical (PEC) NH₃ synthesis on the hierarchical free-standing Au/K_x MoO₃ /Mo/K_x MoO₃ /Au nanoarrays. Endowed with energetically hot electrons and catalytically active sites, the plasmonic nanoarrays exhibit an efficient PEC NH₃ synthesis rate of 9.6 µg cm^-2 h^-1 under visible light irradiation, which is among the highest PEC NRR systems. This work demonstrates the rationally designed plasmonic nanoarrays for highly efficient NH₃ synthesis, which paves a new path for PEC catalytic reactions driven by surface plasmons and future monolithic PEC devices for direct artificial photosynthesis.

Modulating the Active Sites of Oxygen-Deficient TiO2 by Copper Loading for Enhanced Electrocatalytic Nitrogen Reduction to Ammonia

The electrocatalytic nitrogen reduction reaction (NRR) provides a sustainable route for NH₃ synthesis. However, the process is plagued by the strong NN triple bond and high reaction barrier. Modification of catalyst surface to increase N₂ adsorption and activation is crucial. Herein, copper nanoparticles are loaded on the oxygen-deficient TiO₂ , which exhibits an enhanced NRR performance with NH₃ yield of 13.6 µg mg_cat ^-1 h^-1 at -0.5 V versus reversible hydrogen electrode (RHE) and Faradaic efficiency of 17.9% at -0.4 V versus RHE compared to the pristine TiO₂ . The enhanced performance is ascribed to the higher electrochemically active surface area, promoted electron transfer, and increased electron density originated from the strong metal-support interaction (SMSI) between Cu nanoparticles and oxygen-deficient TiO₂ . The SMSI effect also results in lopsided local charge distribution, which polarizes the adsorbed N₂ molecules for better activation. This work provides a facile strategy toward the electrocatalyst design for efficient NRR under ambient conditions.

Formation of Interfacial Cu-[OX ]-Ce Structures with Oxygen Vacancies for Enhanced Electrocatalytic Nitrogen Reduction

Electrochemical nitrogen reduction powered by renewable electricity is a promising strategy to produce ammonia. However, the lack of efficient yet cheap electrocatalysts remains the biggest challenge. Herein, hybrid Cu₂ O-CeO₂ -C nanorods are prepared on copper mesh through a metal-organic framework template route. The Cu-loaded Ce-MOF is thermally converted to Cu₂ O-CeO₂ heterojunctions with interfacial Cu-[O_X ]-Ce structures embedded in carbon. Theoretical calculations reveal the lower formation energy of oxygen vacancies in Cu-[O_X ]-Ce structures than in the Cu₂ O or CeO₂ phase. The Cu-[O_X ]-Ce structures with oxygen vacancies enable the formation of interfacial electron-rich Cu(I) species which show significantly enhanced performance toward electrocatalytic nitrogen reduction with an NH₃ yield of 6.37 × 10^-3  µg s^-1 cm^-2 and a Faradaic efficiency of 18.21% in 0.10 m KOH at -0.3 V versus reversible hydrogen electrode. This work highlights the importance of modulation of charge distribution of Cu-based electrocatalysts to boost the activity toward nitrogen reduction.

Oxygen vacancy engineering of novel ultrathin Bi12O17Br2 nanosheets for boosting photocatalytic N2 reduction

The conversion of N₂ to NH₃ is one of the most promising processes in maintaining natural life and chemical production. Photocatalytic nitrogen reduction reaction (NRR) has the advantage of clean and sustainable, which is considered to be an ideal synthesis technology. In this work, we report the successful synthesis of Bi₁₂O₁₇Br₂ ultrathin nanosheets through simple alkali treatment and solvothermal method. The Bi₁₂O₁₇Br₂ ultrathin nanosheets can improve the separation of carriers and the transfer of photogenerated electrons to N₂ molecules, thus improving the photocatalytic efficiency. Of note, the higher Bi/Br atomic ratio in Bi₁₂O₁₇Br₂ is beneficial to broaden the light absorption edge, and the high concentration of O atoms is easy to produce oxygen vacancies on the surface during the synthesis process of Bi₁₂O₁₇Br₂. The abundant oxygen vacancies and high specific surface area enable N₂ molecules and water to have powerful chemical adsorption and activation. In addition, the photocatalytic reduction of N₂ to NH₃ in pure water shows excellent and stable performance, and the average generation rate of NH₃ reaches up to 620.5 μmol·L^-1·h^-1. This study discovers that rich oxygen vacancies and ultrathin morphology may have a significant part in the process of the photocatalytic nitrogen reduction reaction.

Dehydrated UiO-66(SH)2 : The Zr-O Cluster and Its Photocatalytic Role Mimicking the Biological Nitrogen Fixation

This work reports the dehydrated Zr-based MOF UiO-66(SH)₂ as a visible-light-driven photocatalyst to mimic the biological N₂ fixation process. The ¹⁵ N₂ and other control experiments demonstrated that the new photocatalyst is highly efficient in converting N₂ to ammonia. In-situ TGA, XPS, and EXAFS as well as first-principles simulations were used to demonstrate the role of the thermal treatment and the changes of the local structures around Zr due to the dehydration. It was shown that the dehydration opened a gate for the entry of N₂ molecules into the [Zr₆ O₆ ] cluster where the strong N≡N bond was broken stepwise by μ-N-Zr type interactions driven by the photoelectrons aided by the protonation. This mechanism was discussed in comparison with the Lowe-Thorneley mechanism proposed for the MoFe nitrogenase, and with emphasis on the [Zr₆ O₆ ] cluster effect and the leading role of photoelectrons over the protonation. The results shed new light on understanding the catalytic mechanism of biological N₂ fixation and open a new way to fix N₂ under mild conditions.

Recent advances in photocatalytic nitrogen fixation and beyond

The traditional synthesis of ammonia is an industrial process with high energy consumption that is not environmentally friendly; thus, it is urgent to develop cost-effective approaches to synthesize ammonia under ambient conditions. In recent years, the photochemical synthesis of ammonia has become a hot research frontier. In this mini review, we summarize the recent advances in materials sciences for photocatalytic nitrogen fixation. Beyond nitrogen fixation, we talk about an alternative for artificial ammonia synthesis and coupling reactions with other reactions for the synthesis of other high-value chemicals. The results and findings of this review will help the development of ammonia synthesis and the synthesis of other high-value chemicals.

Plasmonic Photoelectrochemical Coupling Reactions of para-Aminobenzoic Acid on Nanostructured Gold Electrodes

Surface plasmon resonance (SPR) bridges photonics and photoelectrochemistry by providing an effective interaction between absorption and confinement of light to surface electrons of plasmonic metal nanostructures (PMNs). SPR enhances the Raman intensity enormously in surface-enhanced Raman spectroscopy (SERS) and leads to the plasmon-mediated chemical reaction on the surface of nanostructured metal electrodes. To observe variations in chemical reactivity and selectivity, we studied the SPR photoelectrochemical reactions of para-aminobenzoic acid (PABA) on nanostructured gold electrodes. The head-to-tail coupling product "4-[(4-imino-2,5-cyclohexadien-1-ylidene)amino]benzoic acid (ICBA)" and the head-to-head coupling product p,p'-azodibenzoate (ADBA) were obtained from PABA adsorbed on PMN-modified gold electrodes. In particular, under acidic and neutral conditions, ICBA was obtained as the main product, and ADBA was obtained as the minor product. At the same time, under basic conditions, ADBA was obtained as the major product, and ICBA was obtained as the minor product. We have also provided sufficient evidence for the oxidation of the tail-to-tail coupling reaction product that occurred in a nonaqueous medium rather than in an aqueous medium. The above finding was validated by the cyclic voltammetry, SERS, and theoretical calculation results of possible reaction intermediates, namely, 4-aminophenlylenediamine, 4-hydroxyphenlylenediamine, and benzidine. The theoretical adsorption model and experimental results indicated that PABA has been adsorbed as para-aminobenzoate on the gold cluster in a bidentate configuration. This work offers a new view toward the modulation of selective surface catalytic coupling reactions on PMN, which benefits the hot carrier transfer efficiency at photoelectrochemical interfaces.

Engineering Bimodal Oxygen Vacancies and Pt to Boost the Activity Toward Water Dissociation

Water dissociation is the rate-limiting step of several energy-related reactions due to the high energy barrier required for breaking the oxygen-hydrogen bond. In this work, a bimodal oxygen vacancy (V_O ) catalysis strategy is adopted to boost the efficient water dissociation on Pt nanoparticles. The single facet-exposed TiO₂ surface and NiO_x nanocluster possess two modes of V_O different from each other. In ammonia borane hydrolysis, the highest catalytic activity among Pt-based materials is achieved with the turnover frequency of 618 min^-1 under alkaline-free conditions at 298 K. Theoretical simulation and characterization analyses reveal that the bimodal V_O significantly promotes the water dissociation in two ways. First, an ensemble-inducing effect of Pt and V_O in TiO₂ drives the activation of water molecules. Second, an electron promoter effect induced by the electron transfer from V_O in NiO_x to Pt further enhances the ability of Pt to dissociate water and ammonia borane. This insight into bimodal V_O catalysis establishes a new avenue to rationally design heterogeneous catalytic materials in the energy chemistry field.

Light induced ammonia synthesis by crystalline polyoxometalate-based hybrid frameworks coupled with the Sv-1T MoS2 cocatalyst

A series of crystalline polyoxometalate-based hybrid frameworks coupled with rich sulfur vacancy 1T MoS2 through the hydrothermal growth strategy are presented towards light induced ammonia synthesis.

Assembling Lanthanide–Transition Metal Clusters on TiO2 for Photocatalytic Nitrogen Fixation

Ammonia synthesis using light with low energy consumption offers an effective solution for energy saving and environmental protection. Herein, an abundant oxygen vacancy photocatalyst was synthesized via the integration of...

A Schottky-Barrier-Free Plasmonic Semiconductor Photocatalyst for Nitrogen Fixation in a "One-Stone-Two-Birds" Manner

Plasmonic photocatalysis has received much attention owing to attractive plasmonic enhancement effects in improving the solar-to-chemical conversion efficiency. However, the photocatalytic efficiencies have remained low mainly due to the short carrier lifetime caused by the rapid recombination of plasmon-generated hot charge carriers. Although plasmonic metal-semiconductor heterostructures can improve the separation of hot charge carriers, a large portion of the hot charge carriers are lost when they cross the Schottky barrier. Herein, a Schottky-barrier-free plasmonic semiconductor photocatalyst, MoO_{3- x} , which allows for efficient N₂ photofixation in a "one-stone-two-birds" manner, is demonstrated. The oxygen vacancies in MoO_{3- x} serve as the "stone." They "kill two birds" by functioning as the active sites for the chemisorption of N₂ molecules and inducing localized surface plasmon resonance for the generation of hot charge carriers. Benefiting from this unique strategy, plasmonic MoO_{3- x} exhibits a remarkable photoreactivity for NH₃ production up to the wavelength of 1064 nm with apparent quantum efficiencies over 1%, and a solar-to-ammonia conversion efficiency of 0.057% without any hole scavenger. This work shows the great potential of plasmonic semiconductors to be directly used for photocatalysis. The concept of the Schottky-barrier-free design will pave a new path for the rational design of efficient photocatalysts.

Recent Advances in Plasmonic Photocatalysis Based on TiO2 and Noble Metal Nanoparticles for Energy Conversion, Environmental Remediation, and Organic Synthesis

Plasmonic photocatalysis has emerged as a prominent and growing field. It enables the efficient use of sunlight as an abundant and renewable energy source to drive a myriad of chemical reactions. For instance, plasmonic photocatalysis in materials comprising TiO₂ and plasmonic nanoparticles (NPs) enables effective charge carrier separation and the tuning of optical response to longer wavelength regions (visible and near infrared). In fact, TiO₂ -based materials and plasmonic effects are at the forefront of heterogeneous photocatalysis, having applications in energy conversion, production of liquid fuels, wastewater treatment, nitrogen fixation, and organic synthesis. This review aims to comprehensively summarize the fundamentals and to provide the guidelines for future work in the field of TiO₂ -based plasmonic photocatalysis comprising the above-mentioned applications. The concepts and state-of-the-art description of important parameters including the formation of Schottky junctions, hot electron generation and transfer, near field electromagnetic enhancement, plasmon resonance energy transfer, scattering, and photothermal heating effects have been covered in this review. Synthetic approaches and the effect of various physicochemical parameters in plasmon-mediated TiO₂ -based materials on performances are discussed. It is envisioned that this review may inspire and provide insights into the rational development of the next generation of TiO₂ -based plasmonic photocatalysts with target performances and enhanced selectivities.

Amorphization and defect engineering in constructing ternary composite Ag/PW10V2/am-TiO2−x for enhanced photocatalytic nitrogen fixation

Ag/PW10V2/am-TiO2−x was designed by decorating OVs-enriched am-TiO2−x with Ag NPs and PW10V2. The formed Z-scheme heterojunction, Ag–am-TiO2−x interface and plentiful surface OVs account for its high photocatalytic efficiency in nitrogen fixation.

(Plasmonic gold core)@(ultrathin ruthenium shell) nanostructures as antenna-reactor photocatalysts toward nitrogen photofixation

Ruthenium (Ru) is known as the optimal metal catalyst for ammonia (NH₃) synthesis, but the poor light-harvesting capability restricts its application in photocatalysis. Herein, we construct an antenna-reactor nanostructure through the controllable growth of an ultrathin Ru nanocluster shell with desired catalytic activity on the plasmonic gold (Au) nanoantennas. In this nanostructure, Au nanoantennas interact strongly with light to generate hot carriers, meanwhile Ru nanoclusters adsorb and activate N₂, leading to the reduction of N₂ to NH₃ by the generated hot electrons. This antenna-reactor plasmonic photocatalyst exhibits shell-thickness-dependent photocatalytic activity toward nitrogen (N₂) photofixation under visible and near-infrared light illumination.

Emerging Materials and Methods toward Ammonia-Based Energy Storage and Conversion

Efficient storage and conversion of renewable energies is of critical importance to the sustainable growth of human society. With its distinguishing features of high hydrogen content, high energy density, facile storage/transportation, and zero-carbon emission, ammonia has been recently considered as a promising energy carrier for long-term and large-scale energy storage. Under this scenario, the synthesis, storage, and utilization of ammonia are key components for the implementation of ammonia-mediated energy system. Being different from fossil fuels, renewable energies normally have intermittent and variable nature, and thus pose demands on the improvement of existing technologies and simultaneously the development of alternative methods and materials for ammonia synthesis and storage. The energy release from ammonia in an efficient manner, on the other hand, is vital to achieve a sustainable energy supply and complete the nitrogen circle. Herein, recent advances in the thermal-, electro-, plasma-, and photocatalytic ammonia synthesis, ammonia storage or separation, ammonia thermal/electrochemical decomposition and conversion are summarized with the emphasis on the latest developments of new methods and materials (catalysts, electrodes, and sorbents) for these processes. The challenges and potential solutions are discussed.

Hierarchically Porous Metal-Organic Framework/MoS2 Interface for Selective Photocatalytic Conversion of CO2 with H2 O into CH3 COOH

Metal-organic frameworks (MOFs) provide a platform to design new heterogeneous catalysts for catalytic CO₂ reduction, but selective formation of C2 valuable liquid fuel products remains a challenge. Herein, we propose a strategy to synthesize composites by integrating MoS₂ nanosheets into hierarchically porous defective UiO-66 (d-UiO-66) to form Mo-O-Zr bimetallic sites on the interfaces between UiO-66 and MoS₂ . The active interfaces are favorable for the efficient transfer of photo-generated charge carriers and for promoting the activity, whereas, the synergy of the components at the interfaces achieves selectivity for C2 production. The d-UiO-66/MoS₂ composite facilitates the photo-catalytic conversion of gas phase CO₂ and H₂ O to CH₃ COOH under visible light irradiation without any other adducts. The evolution rate and selectivity of CH₃ COOH reached 39.0 μmol g^-1  h^-1 and 94 %, respectively, without any C1 products, suggesting a new approach for the design of highly efficient photocatalysts of CO₂ for C2 production. Theoretical calculations demonstrate the charge-polarized Zr-O-Mo aided the C-C coupling process with the largely reduced energy barrier.

Emerging two-dimensional nanomaterials for electrochemical nitrogen reduction

Ammonia (NH₃) is essential to serve as the biological building blocks for maintaining organism function, and as the indispensable nitrogenous fertilizers for increasing the yield of nutritious crops. The current Haber-Bosch process for industrial NH₃ production is highly energy- and capital-intensive. In light of this, the electroreduction of nitrogen (N₂) into valuable NH₃, as an alternative, offers a sustainable pathway for the Haber-Bosch transition, because it utilizes renewable electricity and operates under ambient conditions. Identifying highly efficient electrocatalysts remains the priority in the electrochemical nitrogen reduction reaction (NRR), marking superior selectivity, activity, and stability. Two-dimensional (2D) nanomaterials with sufficient exposed active sites, high specific surface area, good conductivity, rich surface defects, and easily tunable electronic properties hold great promise for the adsorption and activation of nitrogen towards sustainable NRR. Therefore, this Review focuses on the fundamental principles and the key metrics being pursued in NRR. Based on the fundamental understanding, the recent efforts devoted to engineering protocols for constructing 2D electrocatalysts towards NRR are presented. Then, the state-of-the-art 2D electrocatalysts for N₂ reduction to NH₃ are summarized, aiming at providing a comprehensive overview of the structure-performance relationships of 2D electrocatalysts towards NRR. Finally, we propose the challenges and future outlook in this prospective area.

Plasmon-Enhanced, Self-Traced Nanomotors on the Surface of Silicon

Light-driven nanomotors have attracted much attention due to their potential applications. The movement of conventional nanomotors typically occurs in the solution phase, which limits their application fields. Utilizing visible light to drive nanomotors at the solid-liquid interface represents a grand challenge due to the large friction force between the nanomotor and the solid surface. Based on the attractive plasmon resonance of Au nanocrystals, for the first time, plasmon-enhanced Au nanocrystal-based nanomotors moving at the silicon-aqueous solution interface have been developed. Such nanomotors move with a clear trace engraved on the Si surface, representing an excellent and exceptional self-traced nanomotor system. In addition, the nanomotor trace on the Si surface also provides a unique and promising approach to the fabrication of nanoscale Si patterns, which is central to many applications, including microelectronics, sensing, information storage, and optoelectronics.

Single-Atom (Iron-Based) Catalysts: Synthesis and Applications

Supported single-metal atom catalysts (SACs) are constituted of isolated active metal centers, which are heterogenized on inert supports such as graphene, porous carbon, and metal oxides. Their thermal stability, electronic properties, and catalytic activities can be controlled via interactions between the single-metal atom center and neighboring heteroatoms such as nitrogen, oxygen, and sulfur. Due to the atomic dispersion of the active catalytic centers, the amount of metal required for catalysis can be decreased, thus offering new possibilities to control the selectivity of a given transformation as well as to improve catalyst turnover frequencies and turnover numbers. This review aims to comprehensively summarize the synthesis of Fe-SACs with a focus on anchoring single atoms (SA) on carbon/graphene supports. The characterization of these advanced materials using various spectroscopic techniques and their applications in diverse research areas are described. When applicable, mechanistic investigations conducted to understand the specific behavior of Fe-SACs-based catalysts are highlighted, including the use of theoretical models.

Plasmonic Photoelectrochemistry: In View of Hot Carriers

Utilizing plasmon-generated hot carriers to drive chemical reactions has emerged as a popular topic in solar photocatalysis. However, a complete description of the underlying mechanism of hot-carrier transfer in photochemical processes remains elusive, particularly for those involving hot holes. Photoelectrochemistry enables to localize hot holes on photoanodes and hot electrons on photocathodes and thus offers an approach to separately explore the hole-transfer dynamics and electron-transfer dynamics. This review summarizes a comprehensive understanding of both hot-hole and hot-electron transfers from photoelectrochemical studies on plasmonic electrodes. Additionally, working principles and applications of spectroelectrochemistry are discussed for plasmonic materials. It is concluded that photoelectrochemistry provides a powerful toolbox to gain mechanistic insights into plasmonic photocatalysis.

Synergistic Integration of AuCu Co-Catalyst with Oxygen Vacancies on TiO2 for Efficient Photocatalytic Conversion of CO2 to CH4

Photocatalytic reduction of CO₂ toward eight-electron CH₄ product with simultaneously high conversion efficiency and selectivity remains great challenging owing to the sluggish charge separation and transfer kinetics and lack of active sites for the adsorption and activation of reactants. Herein, a defective TiO₂ nanosheet photocatalyst simultaneously equipped with AuCu alloy co-catalyst and oxygen vacancies (AuCu-TiO_2-x NSs) was rationally designed and fabricated for the selective conversion of CO₂ into CH₄. The experimental results demonstrated that the AuCu alloy co-catalyst not only effectively promotes the separation of photogenerated electron-hole pairs but also acts as synergistic active sites for the reduction of CO₂. The oxygen vacancies in TiO₂ contribute to the separation of charge carriers and, more importantly, promote the oxidation of H₂O, thus providing rich protons to promote the deep reduction of CO₂ to CH₄. Consequently, the optimal AuCu-TiO_2-x nanosheets (NSs) photocatalyst achieves a CO₂ reduction selectivity toward CH₄ up to 90.55%, significantly higher than those of TiO_2-x NSs (31.82%), Au-TiO_2-x NSs (38.74%), and Cu-TiO_2-x NSs (66.11%). Furthermore, the CH₄ evolution rate over the AuCu-TiO_2-x NSs reaches 22.47 μmol·g^-1·h^-1, which is nearly twice that of AuCu-TiO₂ NSs (12.10 μmol·g^-1·h^-1). This research presents a unique insight into the design and synthesis of photocatalyst with oxygen vacancies and alloy metals as the co-catalyst for the highly selective deep reduction of CO₂.

Oxygen and Titanium Vacancies in a BiOBr/MXene-Ti3C2 Composite for Boosting Photocatalytic N2 Fixation

Solar energy can be used as "green" energy by photocatalysis for the nitrogen fixation under the atmospheric conditions compared with the traditional energy-intensive industrial production of ammonia. However, the complex kinetics and high reaction barriers greatly hinder the development of the photocatalytic N₂ reduction reaction. Herein, a BiOBr/MXene-Ti₃C₂ composite catalyst is prepared by the simple electrostatic adsorption and self-assembly method. The as-prepared 10 wt % BiOBr/Ti₃C₂ exhibits the best performance for N₂ fixation to NH₃ by photocatalysis. The evolution rate of NH₃ is up to 234.6 μmol·g^-1·h^-1, which is approximately 48.8 times and 52.4 times higher than those of pure BiOBr and Ti₃C₂, respectively. It is found that the designed double vacancies of oxygen and titanium for BiOBr/Ti₃C₂ composites, with the availability of localized electrons, have the ability to adsorb and activate N₂, which can be efficiently reduced to NH₃ by the interfacial electrons transferred from the excited BiOBr/Ti₃C₂ composite. In addition, the results of in situ Fourier transform infrared show the generation of N_xH_y species by the continuous protonation processes. Moreover, titanium vacancy (V_Ti) induces a strong absorption energy for nitrogen atoms on the surface of BiOBr/Ti₃C₂ according to the density functional theory calculations. In particular, the P-electron feedback caused by V_Ti could effectively promote the weakening of the N≡N triple bond and elongate the N₂ bond length by ∼31.6%. This work might provide new insights into the synergistic effect of double defects and inspiration for the rational design of catalysts by defect engineering in the field of catalytic synthesis of ammonia.

Plasmon-enabled N2 photofixation on partially reduced Ti3C2 MXene

Benefiting from the superior conductivity, rich surface chemistry and tunable bandgap, Ti₃C₂ MXene has become a frontier cocatalyst material for boosting the efficiency of semiconductor photocatalysts. It has been theoretically predicted to be an ideal material for N₂ fixation. However, the realization of N₂ photofixation with Ti₃C₂ as a host photocatalyst has so far remained experimentally challenging. Herein, we report on a sandwich-like plasmon- and an MXene-based photocatalyst made of Au nanospheres and layered Ti₃C₂, and demonstrate its efficient N₂ photofixation in pure water under ambient conditions. The abundant low-valence Ti (Ti^(4-x)+) sites in partially reduced Ti₃C₂ (r-Ti₃C₂) produced by surface engineering through H₂ thermal reduction effectively capture and activate N₂, while Au nanospheres offer plasmonic hot electrons to reduce the activated N₂ into NH₃. The Ti^(4-x)+ active sites and plasmon-generated hot electrons work in tandem to endow r-Ti₃C₂/Au with remarkably enhanced N₂ photofixation activity. Importantly, r-Ti₃C₂/Au exhibits ultrahigh selectivity without the occurrence of competing H₂ evolution. This work opens up a promising route for the rational design of efficient MXene-based photocatalysts.

Tuning the exposure of BiVO4-{010} facets to enhance the N2 photofixation performance

Effective separation of photoexcited carriers and chemisorption of the N₂ molecule are two key issues to efficient nitrogen photofixation. The spatial charge separation of BiVO₄ with anisotropic exposed facets, namely the transfer of photoexcited electrons and holes to {010} and {110} facets, respectively, helps to enhance the separation ability of photogenerated carriers. Theoretical calculation results predict that a surface oxygen vacancy is easier to form on the (010) facet than on the (110) facet of BiVO₄. Accordingly, in this study, enhanced N₂ photofixation performance has been achieved for the first time by tuning the exposure of {010} facets of BiVO₄.

Effective separation of photoexcited carriers and chemisorption of the N₂ molecule are two key issues to efficient nitrogen photofixation.

Piezo-enhanced activation of dinitrogen for room temperature production of ammonia

The catalytic conversion of nitrogen to ammonia remains an energy-intensive process, demanding advanced concepts for nitrogen fixation. The major obstacle of nitrogen fixation lies in the intrinsically high bond energy (941 kJ mol^-1) of the N≡N molecule and the absence of a permanent dipole in N₂. This kinetic barrier is addressed in this study by an efficient piezo-enhanced gold catalysis as demonstrated by the room temperature reduction of dinitrogen into ammonia. Au nanostructures were immobilized on thin film piezoelectric support of potassium sodium niobate (K_0.5Na_0.5NbO₃, KNN) by chemical vapor deposition of a new Au(III) precursor [Me₂Au(PyTFP)(H₂O)]1(PyTFP = (Z)-3,3,3-trifluoro-1-(pyridin-2-yl)-prop-1-en-2-olate) that exhibited high volatility (60 °C, 10^-3mbar) and clean decomposition mechanism to produce well adherent elemental gold films on KNN and Ti substrates. The gold-functionalized KNN films served as an efficient catalytic system for ammonia production with a Faradaic efficiency of 18.9% achieved upon ultrasonic actuation. Our results show that the spontaneous polarization of piezoelectric materials under external electrical fields augments the sluggish electron transfer kinetics by creating instant dipoles in adsorbed N₂molecules to deliver a piezo-enhanced catalytic system promising for sustained activation of dinitrogen molecules.

Charge-transfer dynamics at a Ag/Ni-MOF/Cu2O heterostructure in photoelectrochemical NH3 production

Ag-decorated ultrathin Ni-MOF on Cu₂O was fabricated for the first time. The charge-transfer dynamics at the heterostructure was studied by ultrafast transient absorption spectroscopy in depth. An NH₃ yield rate of 4.63 μg h^-1 cm^-2 with a faradaic efficiency of 24.3% has been achieved. DFT calculations further supported to further comprehend the nitrogen reduction reaction mechanism.

Rational design of photocatalysts for ammonia production from water and nitrogen gas

Photocatalytic N2 reduction has emerged as one of the most attractive routes to produce NH3 as a useful commodity for chemicals used in industries and as a carbon-free energy source. Recently, significant progress has been made in understanding, exploring, and designing efficient photocatalyst. In this review, we outline the important mechanistic and experimental procedures for photocatalytic NH3 production. In addition, we review effective strategies on development of photocatalysts. Finally, our analyses on the characteristics and modifications of photocatalysts have been summarized, based on which we discuss the possible future research directions, particularly on preparing more efficient catalysts. Overall, this review provides insights on improving photocatalytic NH3 production and designing solar-driven chemical conversions.

Synthesis of Ni modified Au@CdS core-shell nanostructures for enhancing photocatalytic coproduction of hydrogen and benzaldehyde under visible light

The development of visible light responsive photocatalysts for simultaneous production of hydrogen (H₂) fuel and value-added chemicals is greatly promising to solve the energy and environmental issues by improving the utilization efficiency of solar energy. Herein, the three-component Ni/(Au@CdS) core-shell nanostructures were constructed by the hydrothermal synthesis followed with photodeposition. The intimate integration of plasmonic Au nanospheres and visible-light responsive CdS shells modified with Ni cocatalyst facilitated the generation and separation of electron-hole pairs as well as reduced the overpotential of hydrogen evolution. The Ni/(Au@CdS) photocatalyst exhibited excellent performance toward the selective transformation of benzyl alcohol under anaerobic conditions, and the yields of H₂ and benzaldehyde reached up to 3882 and 4242 μmol·g^-1·h^-1, respectively. The apparent quantum efficiency (AQE) was determined to be 4.09% under the irradiation of 420 nm. The systematic studies have verified the synergy of plasmonic effect and metal cocatalyst on enhancing the photocatalysis. This work highlights the desirable design and potential application of plasmonic photocatalysts for solar-driven coproduction of H₂ fuel and high-value chemicals.

How to Utilize Excited Plasmon Energy Efficiently

Plasmonic nanoparticles can concentrate electromagnetic fields at the nanoscale and function as a powerful intermediary to enhance light-matter interactions. They have been widely employed for solar energy harvesting, photocatalysis, medicine, sensing, imaging, spectroscopy, optics, and optoelectronics. In this Perspective, we provide a brief overview of research progress in the utilization of excited plasmon energy, with emphasis on the charge- and energy-transfer processes. We discuss important factors that affect the charge- and energy-transfer efficiencies and present open questions and major challenges in the efficient utilization of excited plasmon energy.

Highly Active PdO/Mn3 O4 /CeO2 Nanocomposites Supported on One Dimensional Halloysite Nanotubes for Photoassisted Thermal Catalytic Methane Combustion

In this work, we have successfully triggered the aqueous auto-redox reactions between reductive Ce(OH)₃ and oxidative MnO₄ ^- /Pd²⁺ ions to form PdO/Mn₃ O₄ /CeO₂ (PMC) nanocomposites. PMC could spontaneously self-assemble into compact encapsulation on the surface of halloysite nanotubes (HNTs) to form the final one dimensional HNTs supported PMCs (HPMC). It is identified that there exists strong synergistic effects among the components of PdO, Mn₃ O₄ , and CeO₂ , and hence HPMC could show excellent performance on photoassisted thermal catalytic CH₄ combustion that its light-off temperature was sharply reduced to be 180 °C under visible light irradiation. Based on detailed studies, it is found that the catalytic reaction process well follows the classic MVK mechanism, and adsorption/activation of O₂ into active oxygen species (O*) should be the rate-determining step for CH₄ conversion.

Role of Femtosecond Pulsed Laser-Induced Atomic Redistribution in Bimetallic Au-Pd Nanorods on Optoelectronic and Catalytic Properties

Utilizing solar energy for chemical transformations has attracted a growing interest in promoting the clean and modular chemical synthesis approach and addressing the limitations of conventional thermocatalytic systems. Under light irradiation, noble metal nanoparticles, particularly those characterized by localized surface plasmon resonance, commonly known as plasmonic nanoparticles, generate a strong electromagnetic field, excited hot carriers, and photothermal heating. Plasmonic nanoparticles enabling efficient absorption of light in the visible range have moderate catalytic activities. However, the catalytic performance of a plasmonic nanoparticle can be significantly enhanced by incorporating a highly catalytically active metal domain onto its surface. In this study, we demonstrate that femtosecond laser-induced atomic redistribution of metal domains in bimetallic Au-Pd nanorods (NRs) can enhance its photocurrent response by 2-fold compared to parent Au-Pd NRs. We induce structure changes on Au-Pd NRs by irradiating them with a femtosecond pulsed laser at 808 nm to precisely redistribute Pd atoms on AuNR surfaces, resulting in modified electronic and optical properties and, thereby, enhanced catalytic activity. We also investigate the trade-off between the effect of light absorption and catalytic activity by optimizing the structure and composition of bimetallic Au-Pd nanoparticles. This work provides insight into the design of hybrid plasmonic-catalytic nanostructures with well-tailored geometry, composition, and structure for solar-fuel-based applications.

Atomically Dispersed Iron Metal Site in a Porphyrin-Based Metal-Organic Framework for Photocatalytic Nitrogen Fixation

The rational design of photocatalysts for efficient nitrogen (N₂) fixation at ambient conditions is important for revolutionizing ammonia production and quite challenging because the great difficulty lies in the adsorption and activation of the inert N₂. Inspired by a biological molecule, chlorophyll, featuring a porphyrin structure as the photosensitizer and enzyme nitrogenase featuring an iron (Fe) atom as a favorable binding site for N₂via π-backbonding, here we developed a porphyrin-based metal-organic framework (PMOF) with Fe as the active center as an artificial photocatalyst for N₂ reduction reaction (NRR) under ambient conditions. The PMOF features aluminum (Al) as metal node imparting high stability and Fe incorporated and atomically dispersed by residing at each porphyrin ring promoting the adsorption and the activation of N₂, termed Al-PMOF(Fe). Compared with the pristine Al-PMOF, Al-PMOF(Fe) exhibits a substantial enhancement in NH₃ yield (635 μg g^-1_cat.) and production rate (127 μg h^-1 g^-1_cat.) of 82% and 50%, respectively, on par with the best-performing MOF-based NRR catalysts. Three cycles of photocatalytic NRR experimental results corroborate a stable photocatalytic activity of Al-PMOF(Fe). The combined experimental and theoretical results reveal that the Fe-N site in Al-PMOF(Fe) is the active photocatalytic center that can mitigate the difficulty of the rate-determining step in photocatalytic NRR. The possible reaction pathways of NRR on Al-PMOF(Fe) were established. Our study of porphyrin-based MOF for the photocatalytic NRR will provide insight into the rational design of catalysts for artificial photosynthesis.

Altering Hydrogenation Pathways in Photocatalytic Nitrogen Fixation by Tuning Local Electronic Structure of Oxygen Vacancy with Dopant

To avoid the energy-consuming step of direct N≡N bond cleavage, photocatalytic N₂ fixation undergoing the associative pathways has been developed for mild-condition operation. However, it is a fundamental yet challenging task to gain comprehensive understanding on how the associative pathways (i.e., alternating vs. distal) are influenced and altered by the fine structure of catalysts, which eventually holds the key to significantly promote the practical implementation. Herein, we introduce Fe dopants into TiO₂ nanofibers to stabilize oxygen vacancies and simultaneously tune their local electronic structure. The combination of in situ characterizations with first-principles simulations reveals that the modulation of local electronic structure by Fe dopants turns the hydrogenation of N₂ from associative alternating pathway to associative distal pathway. This work provides fresh hints for rationally controlling the reaction pathways toward efficient photocatalytic nitrogen fixation.