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

Fe─S Bond-Mediated Efficient Electron Transfer in Quantum Dots/Metal-Organic Frameworks for Boosting Photoelectrocatalytic Nitrogen Fixation

Effective electron supply to produce ammonia in photoelectrochemical nitrogen reduction reaction (PEC NRR) remains challenging due to the sluggish multiple proton-coupled electron transfer and unfavorable carrier recombination. Herein, InP quantum dots decorated with sulfur ligands (InP QDs-S2-) bound to MIL-100(Fe) as a benchmark catalyst for PEC NRR is reported. It is found that MIL-100(Fe) can combined with InP QDs-S2- via Fe─S bonds as bridge to facilitate the electron transfer by experimental results. The formation of Fe─S bonds can facilitate electron transfer from inorganic S2- ligands of InP QDs to the Fe metal sites of MIL-100(Fe) within 52 ps, ensuring a more efficient electron transfer and electron-hole separation confirmed by the time-resolved spectroscopy. More importantly, the process of photo-induced carrier transfer can be traced by in situ attenuated total reflection surface-enhanced infrared tests, certifying that the effective electron transfer can promote N≡N dissociation and N2 hydrogenation. As a result, InP QDs-S2-/MIL-100(Fe) exhibits prominent performance with an outstanding NH3 yield of 0.58 µmol cm-2 h-1 (3.09 times higher than that of MIL-100(Fe)). This work reveals an important ultrafast dynamic mechanism for PEC NRR in QDs modified metal-organic frameworks, providing a new guideline for the rational design of efficient MOFs photocathodes.

Ti3+-mediated MIL-125(Ti) by metal substitution for boosting photocatalytic N2 fixation

Photocatalysis, which uses sunlight, N2 and H2O to produce NH3, is a more sustainable approach to N2 fixation than the Haber-Bosch process. However, its efficiency is severely limited by the difficulty of activating NN bonds. This work presents metal (M = Cu, Fe, V)-substituted MIL-125(Ti) (MIL-(MTi)) for photocatalytic N2 fixation without using any sacrificial agents. Structural characterizations reveal that the active sites including oxygen vacancies (OV) and Ti3+ species are formed by the resulting crystal distortion due to the partial substitution of Ti4+ by other metal ions (Cu+, Fe2+, V3+) in MIL-125(Ti). MIL-(CuTi) possesses a larger number of OV and Ti3+ compared to MIL-(FeTi) and MIL-(VTi) due to the larger valence difference between Cu+ and Ti4+. These active sites not only promote the adsorption and activation of N2 and H2O, but also facilitate the photogenerated charge mobility. Photogenerated holes oxidize H2O to produce O2 and H+. Photogenerated electrons reduce N2 activated on Ti3+ sites by combining with H+ to form NH4+. Therefore, MIL-(CuTi) shows the highest NH4+ production rate 46.5 µmol·h-1·g-1, which is much higher than that (1.2 µmol·h-1·g-1) of the pristine MIL-125(Ti). This work provides a new insight into rational design for artificial N2 fixation systems by the construction of the active site.

Plasmonic-mediated SC arylation and SS coupling on nanostructured silver electrodes monitored by in situ surface-enhanced Raman spectroscopy

Plasmon-mediated chemical reaction (PMCR) is a highly attractive field of research. Here we report in situ surface-enhanced Raman spectroscopic (SERS) monitoring of plasmonic-mediated SS bond-forming reaction. The reaction is thought to be a self-coupling reaction proceeding by photoinduced aromatic SC bond arylation. Surprisingly, the SC arylation and SS coupling are found to be occurred on both partially oxidized silver and silver nanoparticles. The results demonstrated that silver oxide or hydroxide and small molecule donor sacrifice agent played a crucial role in the reaction. This work facilitates the in-situ manipulation and characterization of the active silver electrode interface in conjunction with electrochemistry, and also establishes a promising new guideline for surface plasmon resonance photocatalytic reactions on metal nanostructures with high efficiency.

Electron repulsion tuned electronic structure of TiO2 by fluorination for efficient and selective photocatalytic ammonia generation

The photocatalytic conversion of nitrogen into high-value ammonia products holds tremendous potential in the global nitrogen cycle. However, the activation of N2 and competition of hydrogen evolution limit the improvement of nitrogen fixation performance. In this study, we developed a fluorinated TiO2 (F-TiO2) using a hydrothermal-annealing method. The incorporation of F dopants not only enhances the adsorption and activation of N2 through electronic structure regulation, but also facilitates an in situ increase in active sites via the electron repulsion effect between F and Ti atoms. In addition, the presence of F on the surface effectively improved the nitrogen supply problem and optimized the nitrogen fixation selectivity for its hydrophobic modulation. The NH3 yield of the F-TiO2 photocatalyst reached 63.8 μmol h-1 g-1, which was 8.5 times higher than that of pure TiO2. And the selectivity experiment showed that the electronic ratio of NH3 to H2 production reached 0.890. This research offers valuable insights for the design of highly efficient and selective nitrogen-fixing photocatalysts.

Modelling Photocatalytic N2 Reduction to Ammonia: Where We Stand and Where We Are Going

Artificial ammonia synthesis via the Haber-Bosch process is environmentally problematic due to the high energy consumption and corresponding CO2 ${_2 }$ emissions, produced during the reaction and before hand in hydrogen production upon methane steam reforming. Photocatalytic nitrogen fixation as a greener alternative to the conventional Haber-Bosch process enables us to perform nitrogen reduction reaction (NRR) under mild conditions, harnessing light as the energy source. Herein, we systematically review first-principles calculations used to determine the electronic/optical properties of photocatalysts, N2 adsorption and to expound possible NRR mechanisms. The most commonly studied photocatalysts for nitrogen fixation are usually modified with dopants, defects, co-catalysts and Z-scheme heterojunctions to prevent charge carrier recombination, improve charge separation efficiency and adjust a band gap to for utilizing a broader light spectrum. Most studies at the atomistic level of modeling are grounded upon density functional theory (DFT) calculations, wholly foregoing excitation effects paramount in photocatalysis. Hence, there is a dire need to consider methods beyond DFT to study the excited state properties more accurately. Furthermore, a few studies have been examined, which include higher level kinetics and macroscale simulations. Ultimately, we show there is still ample room for improvement with regard to first principles calculations and their integration in multiscale models.

Schottky Junctions with Bi@Bi2MoO6 Core-Shell Photocatalysts toward High-Efficiency Solar N2-to-Ammonnia Conversion in Aqueous Phase

The photocatalytic nitrogen reduction reaction (NRR) in aqueous solution is a green and sustainable strategy for ammonia production. Nonetheless, the efficiency of the process still has a wide gap compared to that of the Haber-Bosch one due to the difficulty of N2 activation and the quick recombination of photo-generated carriers. Herein, a core-shell Bi@Bi2MoO6 microsphere through constructing Schottky junctions has been explored as a robust photocatalyst toward N2 reduction to NH3. Metal Bi self-reduced onto Bi2MoO6 not only spurs the photo-generated electron and hole separation owing to the Schottky junction at the interface of Bi and Bi2MoO6 but also promotes N2 adsorption and activation at Bi active sites synchronously. As a result, the yield of the photocatalytic N2-to-ammonia conversion reaches up to 173.40 μmol g-1 on core-shell Bi@Bi2MoO6 photocatalysts, as much as two times of that of bare Bi2MoO6. This work provides a new design for the decarbonization of the nitrogen reduction reaction by the utilization of renewable energy sources.

Construction of Gold/Rhodium Freestanding Superstructures as Antenna-Reactor Photocatalysts for Plasmon-Driven Nitrogen Fixation

Precisely controlling the architecture and spatial arrangement of plasmonic heterostructures offers unique opportunities to tailor the catalytic property, whereas the lack of a wet-chemistry synthetic approach to fabricating nanostructures with high-index facets limits their practical applications. Herein, we describe a universal synthetic strategy to construct Au/Rh freestanding superstructures (SSs) through the selective growth of ordered Rh nanoarrays on high-index-faceted Au nanobipyramids (NBPs). This synthetic strategy works on various metal nanocrystal substrates and can yield diverse Au/Rh and Pd/Rh SSs. Especially, the obtained Au NBP/Rh SSs exhibit high photocatalytic activity toward N2 fixation as a result of the spatially separated architecture, local electric field enhancement, and the antenna-reactor mechanism. Both theoretical and experimental results reveal that the Au NBPs can function as nanoantennas for light-harvesting to generate hot charge carriers for driving N2 fixation, while the Rh nanoarrays can serve as the active sites for N2 adsorption and activation to synergistically promote the overall catalytic activity in the Au NBP/Rh SSs. This work offers new avenues to rationally designing and constructing spatially separated plasmonic photocatalysts for high-efficiency catalytic applications.

Photo-Assisted Li-N2 Batteries with Enhanced Nitrogen Fixation and Energy Conversion

Li-N2 batteries have received widespread attention for their potential to integrate N2 fixation, energy storage, and conversion. However, because of the low activity and poor stability of cathode catalysts, the electrochemical performance of Li-N2 batteries is suboptimal, and their electrochemical reversibility has rarely been proven. In this study, a novel bifunctional photo-assisted Li-N2 battery system was established by employing a plasmonic Au nanoparticles (NPs)-modified defective carbon nitride (Au-Nv -C3 N4 ) photocathode. The Au-Nv -C3 N4 exhibits strong light-harvesting, N2 adsorption, and N2 activation abilities, and the photogenerated electrons and hot electrons are remarkably beneficial for accelerating the discharge and charge reaction kinetics. These advantages enable the photo-assisted Li-N2 battery to achieve a low overpotential of 1.32 V, which is the lowest overpotential reported to date, as well as superior rate capability and prolonged cycle stability (≈500 h). Remarkably, a combination of theoretical and experimental results demonstrates the high reversibility of the photo-assisted Li-N2 battery. The proposed novel strategy for developing efficient cathode catalysts and fabricating photo-assisted battery systems breaks through the overpotential bottleneck of Li-N2 batteries, providing important insights into the mechanism underlying N2 fixation and storage.

Photoelectrochemical-driven nitrogen reduction to ammonia by a Vo-SnO2/TiO2 composite electrode

N2 molecules with the NN triple bond structure are difficult to cleave under mild conditions to achieve the nitrogen fixation reaction. Photoelectrochemical (PEC) catalysis technology combining the advantages of photocatalysis and electrocatalysis provides the possibility of the nitrogen reduction reaction under ambient conditions. Herein, an SnO2/TiO2 photoelectrode was first fabricated through depositing SnO2 quantum dots on TiO2 nanorod arrays via a simple hydrothermal method. The oxygen vacancy (Vo) content was then induced in SnO2 through annealing SnO2/TiO2 at high temperature under an inert atmosphere. The heterogeneous structure of Vo-SnO2 quantum dots and TiO2 nanorods boosted the separation of photocarriers. The photoelectrons generated by photoexcitation were transferred from the conduction band of TiO2 to the conduction band of Vo-SnO2 and trapped by Vo. Vo activates N2 molecules adsorbed on the catalyst surface, and reacts with H+ in the electrolyte to generate NH3. The nitrogen fixation yield of PEC catalysis and its faradaic efficiency can reach 19.41 μg cm-2 h-1, and 59.6% at -0.2 V bias potential, respectively. The heterogeneous structure of Vo-SnO2/TiO2, introduction of Vo and synergistic effect between light and electricity greatly promotes the PEC nitrogen reduction to NH3.

Cu-modified InVO4 photocatalysts for enhanced N2 fixation using chemical reagents and electroplating sludge as the Cu source

Inspired by simulation analysis, we found that Cu decoration could enhance the NH3 production rate of InVO4 through promoting N2 adsorption and reducing the activation energy of the key hydrogenation step. 5% Cu/InVO4 exhibited an optimal NH3 yield of 195.11 μmol gcat-1 h-1, approximately six times higher than that of InVO4. Cu/InVO4 was also fabricated by upcycling Cu from electroplating sludge, achieving a gratifying nitrogen fixation performance of 154.13 μmol gcat-1 h-1.

Nitrate Reduction by NiFe-LDH/CeO2: Understanding the Synergistic Effect between Dual-Metal Sites and Dual Adsorption

Electrocatalytic nitrate reduction reaction (EC-NITRR) shows a significant advantage for green reuse of the nitrate (NO3-) pollutant. However, the slow diffusion reaction limits the reaction rate in practical EC-NITRR, causing an unsatisfactory ammonia (NH3) yield. In this work, a multifunctional NiFe-LDH/CeO2 with the dual adsorption effect (physisorption and chemisorption) and dual-metal sites (Ce3+ and Fe2+) was fabricated by the electrodeposition method. NiFe-LDH/CeO2 performed an expected ability of enrichment for NO3- through the pseudo-first-order and pseudo-second-order kinetic models, and the polymetallic structure provided abundant sites for effective reaction of NO3-. At-0.6 V vs RHE, the ammonia (NH3) yield of NiFe-LDH/CeO2 reached 335.3 μg h-1 cm-2 and the selectivity of NH3 was 24.2 times that of NO2-. The nitrogen source of NH3 was confirmed by 15NO3- isotopic labeling. Therefore, this work achieved the recycling of the NO3- pollutant by synergy of enrichment and catalysis, providing an alternative approach for the recovery of NO3- from wastewater.

Unraveling Synergistic Effect of Defects and Piezoelectric Field in Breakthrough Piezo-Photocatalytic N2 Reduction

Piezo-photocatalysis is a frontier technology for converting mechanical and solar energies into crucial chemical substances and has emerged as a promising and sustainable strategy for N2 fixation. Here, for the first time, defects and piezoelectric field are synergized to achieve unprecedented piezo-photocatalytic nitrogen reduction reaction (NRR) activity and their collaborative catalytic mechanism is unraveled over BaTiO3 with tunable oxygen vacancies (OVs). The introduced OVs change the local dipole state to strengthen the piezoelectric polarization of BaTiO3 , resulting in a more efficient separation of photogenerated carrier. Ti3+ sites adjacent to OVs promote N2 chemisorption and activation through d-π back-donation with the help of the unpaired d-orbital electron. Furthermore, a piezoelectric polarization field could modulate the electronic structure of Ti3+ to facilitate the activation and dissociation of N2 , thereby substantially reducing the reaction barrier of the rate-limiting step. Benefitting from the synergistic reinforcement mechanism and optimized surface dynamics processes, an exceptional piezo-photocatalytic NH3 evolution rate of 106.7 µmol g-1  h-1 is delivered by BaTiO3 with moderate OVs, far surpassing that of previously reported piezocatalysts/piezo-photocatalysts. New perspectives are provided here for the rational design of an efficient piezo-photocatalytic system for the NRR.

Photosynthetic System Based on a Polyoxometalate-Based Dehydrated Metal-Organic Framework for Nitrogen Fixation

In nature, biological nitrogen fixation is accomplished through the π-back-bonding mechanism of nitrogenase, which poses significant challenges for mimic artificial systems, thanks to the activation barrier associated with the N≡N bond. Consequently, this motivates us to develop efficient and reusable photocatalysts for artificial nitrogen fixation under mild conditions. We employ a charge-assisted self-assembly process toward encapsulating one polyoxometalate (POM) within a dehydrated Zr-based metal-organic framework (d-UiO-66) exhibiting nitrogen photofixation activities, thereby constructing an enzyme-mimicking photocatalyst. The dehydration of d-UiO-66 is favorable for facilitating nitrogen chemisorption and activation via the unpaired d-orbital electron at the [Zr6O6] cluster. The incorporation of POM guests enhanced the charge separation in the composites, thereby facilitating the transfer of photoexcited electrons into the π* antibonding orbital of chemisorbed N2 for efficient nitrogen fixation. Simultaneously, the catalytic efficiency of SiW9Fe3@d-UiO-66 is enhanced by 9.0 times compared to that of d-UiO-66. Moreover, SiW9Fe3@d-UiO-66 exhibits an apparent quantum efficiency (AQE) of 0.254% at 550 nm. The tactics of "working-in-tandem" achieved by POMs and d-UiO-66 are extremely vital for enhancing artificial ammonia synthesis. This study presents a paradigm for the development of an efficient artificial catalyst for nitrogen photofixation, aiming to mimic the process of biological nitrogen fixation.

Structure and Defect Engineering Synergistically Boost High Solar-to-Chemical Conversion Efficiency of Cerium oxide/Au Hollow Nanomushrooms for Nitrogen Photofixation

Photocatalytic nitrogen fixation using solar illumination under ambient conditions is a promising strategy for production of the indispensable chemical NH3 . However, due to the catalyst's limitations in solar energy utilization, loss of hot electrons during transfer, and low nitrogen adsorption and activation capacity, the unsatisfactory solar-to-chemical conversion (SCC) efficiencies of most photocatalysts limit their practical applications. Herein, cerium oxide nanosheets with abundant strain-VO defects were anchored on Au hollow nanomushroom through atomically sharp interfaces to construct a novel semiconductor/plasmonic metal hollow nanomushroom-like heterostructure (denoted cerium oxide-AD/Au). Plasmonic Au extended the absorption of light from the visible to the second near-infrared region. The superior interface greatly enhanced the transfer efficiency of hot electrons. Abundant strain-VO defects induced by interfacial compressive strain promoted adsorption and in situ activation of nitrogen, and such synergistic promotion of strain and VO defects was further confirmed by density functional theory calculations. The judicious structural and defect engineering co-promoted the efficient nitrogen photofixation of the cerium oxide-AD/Au heterostructures with a SCC efficiency of 0.1 % under simulated AM 1.5G solar illumination, which is comparable to the average solar-to-biomass conversion efficiency of natural photosynthesis by typical plants, thus exhibiting significant potential as a new candidate for artificial photosynthesis.

Synergistic Spatial Confining Effect and O Vacancy in WO3 Hollow Sphere for Enhanced N2 Reduction

Visible-light-driven N2 reduction into NH3 in pure H2O provides an energy-saving alternative to the Haber-Bosch process for ammonia synthesizing. However, the thermodynamic stability of N≡N and low water solubility of N2 remain the key bottlenecks. Here, we propose a solution by developing a WO3-x hollow sphere with oxygen vacancies. Experimental analysis reveals that the hollow sphere structure greatly promotes the enrichment of N2 molecules in the inner cavity and facilitates the chemisorption of N2 onto WO3-x-HS. The outer layer's thin shell facilitates the photogenerated charge transfer and the full exposure of O vacancies as active sites. O vacancies exposed on the surface accelerate the activation of N≡N triple bonds. As such, the optimized catalyst shows a NH3 generation rate of 140.08 μmol g-1 h-1, which is 7.94 times higher than the counterpart WO3-bulk.

Colloidal Plasmonic TiN Nanoparticles for Efficient Solar Seawater Desalination

Transferring traditional plasmonic noble metal nanomaterials from the laboratory to industrial production has remained challenging due to the high price of noble metals. The development of cost-effective non-noble-metal alternatives with outstanding plasmonic properties has therefore become essential. Herein, we report on the gram-scale production of differently shaped TiN nanoparticles with strong plasmon-enabled broadband light absorption, including differently sized TiN nanospheres, nanobipyramids, and nanorod arrays. The TiN nanospheres and nanobipyramids are further coembedded in highly porous poly(vinyl alcohol) films to function as a photothermal material for solar seawater desalination. A seawater evaporation rate of 3.8 kg m-2 h-1 is achieved, which marks the record performance among all plasmonic solar seawater desalination systems reported so far. The removal percentage of phenol reaches 98.3%, which is attributed to the joint action of the excellent photocatalytic ability and the superhydrophilicity of the porous TiN-based composite film.

Vacancy-Mediated Control of Local Electronic Structure for High-Efficiency Electrocatalytic Conversion of N2 to NH3

Ambient electrocatalytic nitrogen (N2 ) reduction has gained significant recognition as a potential substitute for producing ammonia (NH3 ). However, N2 adsorption and *NN protonation for N2 activation reaction with the competing hydrogen evolution reaction remain a daunting challenge. Herein, a defect-rich TiO2 nanosheet electrocatalyst with PdCu alloy nanoparticles (PdCu/TiO2-x ) is designed to elucidate the reactivity and selectivity trends of N2 cleavage path for N2 -to-NH3 catalytic conversion. The introduction of oxygen vacancy (OV) not only acts as active sites but also effectively promotes the electron transfer from Pd-Cu sites to high-concentration Ti3+ sites, and thus lends to the N2 activation via electron donation of PdCu. OVs-mediated control effectively lowers the reaction barrier of *N2 H and *H adsorption and facilitates the first hydrogenation process of N2 activation. Consequently, PdCu/TiO2-x catalyst attains a high rate of NH3 evolution, reaching 5.0 mmol gcat. -1  h-1 . This work paves a pathway of defect-engineering metal-supported electrocatalysts for high-efficient ammonia electrosynthesis.

Engineering photocatalytic ammonia synthesis

Photocatalytic ammonia synthesis (PAS) is an emerging zero carbon emission technology, which is critical for mitigating energy crises and achieving carbon neutrality. Herein, we summarize the recent advances and challenges in PAS from an engineering perspective based on its whole chain process, i.e., materials engineering, structure engineering and reaction engineering. For materials engineering, we discuss the commonly used photocatalytic materials including metal oxides, bismuth oxyhalides and graphitic carbon nitride and emerging materials, such as organic frameworks, along with the analysis of their characteristics and regulation methods to enhance the PAS performance. For structure engineering, the design of photocatalysts is described in terms of morphology, vacancy and band, corresponding to the crystal, atom and electron scales, respectively. Moreover, the structure-performance relationship of photocatalysts has been deeply explored in this section. For reaction engineering, we identify three key processes from the chemical reaction and mass transfer, i.e., nitrogen activation, molecule transfer and electron transfer, to intensify and optimize the PAS reaction. Hopefully, this review will provide a novel paradigm for the design and preparation of high-efficiency ammonia synthesis photocatalysts and inspire the practical application of PAS.

A Pd-based plasmonic photocatalyst for nitrogen fixation through an antenna-reactor mechanism

Plasmonic metal nanocrystals (e.g., Au, Ag, and Cu) hold great promise for driving photocatalytic reactions, but little is known about the plasmonic properties of Pd nanocrystals. Herein, we constructed a plasmonic Pd/Ru antenna-reactor photocatalyst through the controllable growth of a Ru nanoarray 'reactor' on a Pd nano-octahedron 'antenna' and demonstrated a plasmonic Pd-driven N2 photofixation process. The plasmonic properties of Pd nano-octahedrons were verified using finite-difference time-domain (FDTD) simulations and refractive index sensitivity tests in water-glycerol mixtures. Notably, the constructed plasmonic antenna-reactor nanostructures exhibited superior photocatalytic activities during N2 photofixation, with a maximum ammonia production rate of 117.5 ± 15.0 μmol g-1 h-1 under visible and near-infrared (NIR) light illumination. The mechanism can be attributed to the ability of the plasmonic Pd nanoantennas to harvest light to generate abundant hot electrons and the Ru nanoreactors to provide active sites for adsorption and activation of N2. This work paves the way for the development of Pd-based plasmonic photocatalysts for efficient N2 photofixation and sheds new light on the optimal design and construction of antenna-reactor nanostructures.

The role of 13X molecular sieves in photocatalytic nitrogen fixation

To overcome the weak adsorption and difficult activation of N2 on catalysts in the photocatalytic nitrogen reduction reaction (NRR), we put forward that the introduction of molecular sieve 13X may realize the enrichment and activation of N2. 13X and the photoactive substrate BiOBr were assembled electrostatically to construct composite catalysts. In the presence of 13X, they are rich in nitrogen adsorption and activation sites, and the highest ammonia yield can reach 360.5 μmol h-1 gcat-1. It is surprising to find that 13X is able to optimize the photoelectric properties. This work extends the function of molecular sieves in the NRR and offers guidance to design catalysts with high photocatalytic activity.

Efficient Nitrate Generation through Electrochemical N2 Oxidation with Nickel Oxyhydroxide Decorated Copper Hydroxide Driven by Solar Cells

Electrocatalytic nitrogen oxidation reaction (NOR) into nitrate under ambient conditions, as an alternative to replace traditional industrial method, is a promising artificial N2 fixation strategy, especially powered by renewable energy. Here, through skillfully balancing competitive relationships between NOR and oxygen evolution reaction (OER), the nickel oxyhydroxide decorated Cu(OH)2 hybrid electrocatalyst with Cu:Ni molar ratio of 1:1 is developed, which achieves outstanding Faradaic efficiency (FE) of 18.7% and yield rate of 228.24 µmol h-1  gcat -1 at 2.0 V versus reversible hydrogen electrode (RHE) in the electrolyte of 0.1 m Na2 SO4 . Also, the hybrid catalyst maintained over five cycles (10 h each cycle) with negligible decay in performance. The synergetic effect between the components of nickel oxyhydroxide and Cu(OH)2 is found to remarkably activate N2 and suppress the activity of competitive OER, which enhances NOR performance eventually. Moreover, the conversion efficiency of solar-to-nitrate (STN) with 0.025% was obtained by coupling with a commercial solar cell. This work provides a novel avenue of rational catalysts design strategies and realizes solar-to-nitrate synthesis.

Defective TiO2- x for High-Performance Electrocatalytic NO Reduction toward Ambient NH3 Production

Synthesis of green ammonia (NH₃ ) via electrolysis of nitric oxide (NO) is extraordinarily sustainable, but multielectron/proton-involved hydrogenation steps as well as low concentrations of NO can lead to poor activities and selectivities of electrocatalysts. Herein, it is reported that oxygen-defective TiO₂ nanoarray supported on Ti plate (TiO_{2- x} /TP) behaves as an efficient catalyst for NO reduction to NH₃ . In 0.2 m phosphate-buffered electrolyte, such TiO_{2- x} /TP shows competitive electrocatalytic NH₃ synthesis activity with a maximum NH₃ yield of 1233.2 µg h^-1  cm^-2 and Faradaic efficiency of 92.5%. Density functional theory calculations further thermodynamically faster NO deoxygenation and protonation processes on TiO_{2- x} (101) compared to perfect TiO₂ (101). And the low energy barrier of 0.7 eV on TiO_{2- x} (101) for the potential-determining step further highlights the greatly improved intrinsic activity. In addition, a Zn-NO battery is fabricated with TiO_{2- x} /TP and Zn plate to obtain an NH₃ yield of 241.7 µg h^-1  cm^-2 while providing a peak power density of 0.84 mW cm^-2 .

Steric hindrance-induced selective growth of rhodium on gold nanobipyramids for plasmon-enhanced nitrogen fixation

The construction of an antenna-reactor plasmonic photocatalyst that is composed of a plasmonic and a catalytically active metal holds great promise in driving N2 photofixation, but its photocatalytic performance is highly dependent on the spatial distribution of the two components. Up to now, the fabrication of dumbbell-shaped nanostructures featuring spatially separated architecture has remained challenging. Herein, we develop a facile synthetic strategy for the site-selective growth of a Rh nanocrystal 'reactor' on two tips of an Au nanobipyramid (NBP) 'antenna' through the precise manipulation of steric hindrance toward Rh overgrowth. The obtained Au NBP/tip-Rh nanodumbbells (Au NBP/tip-Rh NDs) can function as an excellent antenna-reactor plasmonic photocatalyst for N2 photofixation. In this scenario, the Au nanoantenna harvests light and generates hot electrons under plasmon resonance, meanwhile the hot electrons are transferred to the active sites on Rh nanocrystals for N2 reduction. In comparison with that of classical core@shell nanostructures, the spatially separated architecture of the Au NBP/tip-Rh NDs facilitates charge separation, greatly improving the photocatalytic activity. This study sheds new light on the structure-function relationship for N2 photofixation and benefits the design and construction of spatially separated plasmonic photocatalysts.

Elucidating the Origin of Plasmon-Generated Hot Holes in Water Oxidation

Plasmon-generated hot electrons in metal/oxide heterostructures have been used extensively for driving photochemistry. However, little is known about the origin of plasmon-generated hot holes in promoting photochemical reactions. Herein, we discover that, during the nonradiative plasmon decay, the interband excitation rather than the intraband excitation generates energetic hot holes that enable to drive the water oxidation at the Au/TiO₂ interface. Distinct from lukewarm holes via the intraband excitation that only remain on Au, hot holes from the interband excitation are found to be transferred from Au into TiO₂ and stabilized by surface oxygen atoms on TiO₂, making them available to oxidize adsorbed water molecules. Taken together, our studies provide spectroscopic evidence to clarify the photophysical process for exciting plasmon-generated hot holes, unravel their atomic-level accumulation sites to maintain the strong oxidizing power in metal/oxide heterostructures, and affirm their crucial functions in governing photocatalytic oxidation reactions.

Boosting charge-transfer in tuned Au nanoparticles on defect-rich TiO2 nanosheets for enhancing nitrogen electroreduction to ammonia production

The electrocatalytic nitrogen reduction reaction (eNRR) to ammonia (NH₃) has been recognized as an effective, carbon-neutral, and great-potential strategy for ammonia production. However, the conversion efficiency and selectivity of eNRR still face significant challenges due to the slow transfer kinetics and lack of effective N₂ adsorption and activation sites in this process. Herein, we designed and fabricated defect-rich TiO₂ nanosheets furnished with oxygen vacancies (OVs) and Au nanoparticles (Au/TiO_2-x) as the electrocatalyst for efficient N₂-fixing. The experimental results demonstrate that OVs act as active sites, which enable efficient chemisorption and activation of N₂ molecules. The Au nanoparticles loaded on the OVs-rich TiO₂ nanosheets not only accelerate charge transfer but also change the local electronic structure, thus enhancing N₂ adsorption and activation. In this work, the optimal Au/TiO_2-x electrocatalyst displays a considerable NH₃ yield activity of 12.5 μg h^-1 mg_cat.^-1 and a faradaic efficiency (FE) of 10.2 % at -0.40 V vs reversible hydrogen electrode (RHE). More importantly, the Au/TiO_2-x exhibits a stable N₂-fixing activity in cycling and it persists even after 80 h of consecutive electrolysis. Density functional theory (DFT) calculations reveal that the OVs serve as the active sites in TiO₂, while Au nanoparticles are crucial for improving N₂ chemisorption and lowering the reaction energy barrier by facilitating the charge transfer for eNRR with a distal hydrogenation pathway. This research offers a rational catalytic site design for modulating charge transfer of active sites on metal-supported defective catalysts to boost N₂ electroreduction to NH₃.

Active Site Engineering on Plasmonic Nanostructures for Efficient Photocatalysis

Plasmonic nanostructures have shown immense potential in photocatalysis because of their distinct photochemical properties associated with tunable photoresponses and strong light-matter interactions. The introduction of highly active sites is essential to fully exploit the potential of plasmonic nanostructures in photocatalysis, considering the inferior intrinsic activities of typical plasmonic metals. This review focuses on active site-engineered plasmonic nanostructures with enhanced photocatalytic performance, wherein the active sites are classified into four types (i.e., metallic sites, defect sites, ligand-grafted sites, and interface sites). The synergy between active sites and plasmonic nanostructures in photocatalysis is discussed in detail after briefly introducing the material synthesis and characterization methods. Active sites can promote the coupling of solar energy harvested by plasmonic metal to catalytic reactions in the form of local electromagnetic fields, hot carriers, and photothermal heating. Moreover, efficient energy coupling potentially regulates the reaction pathway by facilitating the excited state formation of reactants, changing the status of active sites, and creating additional active sites using photoexcited plasmonic metals. Afterward, the application of active site-engineered plasmonic nanostructures in emerging photocatalytic reactions is summarized. Finally, a summary and perspective of the existing challenges and future opportunities are presented. This review aims to deliver some insights into plasmonic photocatalysis from the perspective of active sites, expediting the discovery of high-performance plasmonic photocatalysts.

Defect-induced charge redistribution of MoO3-x nanometric wires for photocatalytic ammonia synthesis

Photocatalytic ammonia synthesis technology has become one of the effective methods to replace the Haber method for nitrogen fixation in the future for its low energy consumption and green environment. However, limited by the weak adsorption/activation ability of N₂ molecules at the photocatalyst interface, the efficient nitrogen fixation still remains a daunting job. Defect-induced charge redistribution as a catalytic site for N₂ molecules is the most prominent strategy to enhance the adsorption/activation of N₂ molecules at the interface of catalysts. In this study, MoO_3-x nanowires containing asymmetric defects were prepared by a one-step hydrothermal method via using glycine as a defect inducer. It is shown that at the atomic scale, the defect-induced charge reconfiguration can significantly improve the nitrogen adsorption and activation capacity and enhance the nitrogen fixation capacity; at the nanoscale, the charge redistribution induced by asymmetric defects effectively improved the photogenerated charge separation. Given the charge redistribution on the atomic and nanoscale of MoO_3-x nanowires, the optimal nitrogen fixation rate of MoO_3-x reached 200.35 µmol g^-1h^-1.

Theoretical exploration of the nitrogen fixation mechanism of two-dimensional dual-metal TM1TM2@C9N4 electrocatalysts

The electrochemical nitrogen reduction reaction (eNRR) to NH₃ has become an alternative to traditional NH₃ production techniques, while developing NRR catalysts with high activity and high selectivity is of great importance. In this study, we systematically investigated the potentiality of dual transition metal (TM) atom anchored electrocatalysts, TM₁TM₂@C₉N₄ (TM₁, TM₂ = 3(4)d TM atoms), for the NRR through the first principles high-throughput screening method. A total of 78 TM₁TM₂@C₉N₄ candidates were designed to evaluate their stability, catalytic activity, and selectivity for the NRR. Four TM₁TM₂@C₉N₄ candidates (TM₁TM₂ = NiRu, FeNi, TiNi, and NiZr) with an end-on N₂ adsorption configuration, and two candidates (TM₁TM₂ = TiNi and TiFe) with a side-on adsorption configuration, were screened out with the advantage of suppressing the hydrogen evolution reaction (HER) and exhibiting high NRR activity. Moreover, the catalysts with end-on and side-on N₂ adsorption configurations were determined to favor distal and consecutive reaction pathways, respectively, with favorable limiting potentials of only -0.33 V to -0.53 V. Detailed analysis showed that the N₂ adsorption and activation are primarily ascribed to the strong back-donation interactions between the d-electrons of TM atoms and the anti-orbitals of an N₂ molecule. Our findings pave a way for the rational design and rapid screening of highly active C₉N₄-based catalysts for the NRR.

High-Performance Photocatalytic Reduction of Nitrogen to Ammonia Driven by Oxygen Vacancy and Ferroelectric Polarization Field of SrBi4 Ti4 O15 Nanosheets

Photo-responsive semiconductors can facilitate nitrogen activation and ammonia production, but the high recombination rate of photogenerated carriers represents a significant barrier. Ferroelectric photocatalysts show great promise in overcoming this challenge. Herein, by adopting a low-temperature hydrothermal procedure with varying concentrations of glyoxal as the reducing agent, oxygen vacancies (Vo) are effectively produced on the surface of ferroelectric SrBi₄ Ti₄ O₁₅ (SBTO) nanosheets, which leads to a considerable increase in photocatalytic activity toward nitrogen fixation under simulated solar light with an ammonia production rate of 53.41 µmol g^-1 h^-1 , without the need of sacrificial agents or photosensitizers. This is ascribed to oxygen vacancies that markedly enhance the self-polarization and internal electric field of ferroelectric SBTO, and hence, facilitate the separation of photogenerated charge carriers and light trapping as well as N₂ adsorption and activation, as compared to pristine SBTO. Consistent results are obtained in theoretical studies. Results from this study highlight the significance of surface oxygen vacancies in enhancing the performance of photocatalytic nitrogen fixation by ferroelectric catalysts.

Metal-Organic Framework-Based Photocatalysis for Solar Fuel Production

Metal-organic frameworks (MOFs) represent a novel class of crystalline inorganic-organic hybrid materials with tunable semiconducting behavior. MOFs have potential for application in photocatalysis to produce sustainable solar fuels, owing to their unique structural advantages (such as clarity and modifiability) that can facilitate a deeper understanding of the structure-activity relationship in photocatalysis. This review takes the photocatalytic active sites as a particular perspective, summarizing the progress of MOF-based photocatalysis for solar fuel production; mainly including three categories of solar-chemical conversions, photocatalytic water splitting to hydrogen fuel, photocatalytic carbon dioxide reduction to hydrocarbon fuels, and photocatalytic nitrogen fixation to high-energy fuel carriers such as ammonia. This review focuses on the types of active sites in MOF-based photocatalysts and discusses their enhanced activity based on the well-defined structure of MOFs, offering deep insights into MOF-based photocatalysis.

Dual-plasmon-enhanced nitrophenol hydrogenation over W18O49–Au heterostructures studied at the single-particle level

The dual-plasmonic W18O49–Au heterostructure exhibited enhanced catalytic performance in nitrophenol hydrogenation. The HEI process and coupling effect were demonstrated by single-particle spectroscopy and FDTD simulation.

Prospects and good experimental practices for photocatalytic ammonia synthesis

The development of photocatalysts is greatly hindered by false positives or non-reproducible data. Here, The authors describe the current known causes of non-reproducible results in the literature and present solutions to mitigate these false positive results.

Symmetry-breaking synthesis of Janus Au/CeO2 nanostructures for visible-light nitrogen photofixation

Precise manipulation of the reactive site spatial distribution in plasmonic metal/semiconductor photocatalysts is crucial to their photocatalytic performance, but the construction of Janus nanostructures through symmetry-breaking synthesis remains a significant challenge. Here we demonstrate a synthetic strategy for the selective growth of a CeO2 semi-shell on Au nanospheres (NSs) to fabricate Janus Au NS/CeO2 nanostructures with the assistance of a SiO2 hard template and autoredox reaction between Ag+ ions and a ceria precursor. The obtained Janus nanostructures possess a spatially separated architecture and exhibit excellent photocatalytic performance toward N2 photofixation under visible-light illumination. In this scenario, N2 molecules are reduced by hot electrons on the CeO2 semi-shell, while hole scavengers are consumed by hot holes on the exposed Au NS surface, greatly promoting the charge carrier separation. Moreover, the exposed Au NS surface in the Janus structures offers an additional opportunity for the fabrication of ternary Janus noble metal/Au NS/CeO2 nanostructures. This work highlights the genuine superiority of the spatially separated nanoarchitectures in the photocatalytic reaction, offering instructive guidance for the design and construction of novel plasmonic photocatalysts.

A broadband and polarization-independent metasurface perfect absorber for hot-electron photoconversion

We report an ultra-broadband metasurface perfect absorber from the UV to NIR region based on TiN nanostructures. A polarization-independent experimental average absorption of 0.900 (0.921 in simulation) at the wavelength band from 300 nm to 1500 nm is realized with only an 82 nm-thick TiN layer with TiO₂ and MgF₂ on top, which is efficiently fabricated by utilizing double-beam UV interference lithography followed by sputter coating deposition. A TiN-TiO₂ hot-electron photoelectric conversion system is also simulated. An IPCE of 4% is realized at the wavelength of 710 nm and the average IPCE is 2.86% in the wavelength range of 400 nm to 1500 nm. The demonstrated device suggests an efficient way of designing and fabricating broadband perfect absorbers, which has great application potential in efficient hot-electron optoelectronic and photocatalytic systems.

Achievements and Perspectives in Metal–Organic Framework-Based Materials for Photocatalytic Nitrogen Reduction

Metal–organic frameworks (MOFs) are coordination polymers with high porosity that are constructed from molecular engineering. Constructing MOFs as photocatalysts for the reduction of nitrogen to ammonia is a newly emerging but fast-growing field, owing to MOFs’ large pore volumes, adjustable pore sizes, controllable structures, wide light harvesting ranges, and high densities of exposed catalytic sites. They are also growing in popularity because of the pristine MOFs that can easily be transformed into advanced composites and derivatives, with enhanced catalytic performance. In this review, we firstly summarized and compared the ammonia detection methods and the synthetic methods of MOF-based materials. Then we highlighted the recent achievements in state-of-the-art MOF-based materials for photocatalytic nitrogen fixation. Finally, the summary and perspectives of MOF-based materials for photocatalytic nitrogen fixation were presented. This review aims to provide up-to-date developments in MOF-based materials for nitrogen fixation that are beneficial to researchers who are interested or involved in this field.

Improved visible light photocatalytic nitrogen fixation activity using a FeII-rich MIL-101(Fe): breaking the scaling relationship by photoinduced FeII/FeIII cycling

The scaling relations between nitrogen adsorption and NH_x destabilization are key challenges to the widespread adoption of the photocatalytic synthesis of ammonia. In this work, a Fe^II-rich MIL-101(Fe) (MIL-101(Fe^II/Fe^III)) was synthesized using a one-step solvent thermal method with ethylene glycol (EG) as a reducing agent, which can break the scaling relationship by photoinduced Fe^II (high nitrogen adsorption ability) and Fe^III (high NH_z destabilization ability) cycling. XPS was used to detect the change in iron valence state in the MIL-101(Fe^II/Fe^III) material. The photocatalytic nitrogen fixation efficiency of MIL-101(Fe^II/Fe^III) under visible light without any sacrificial agent was 466.8 μmol h^-1 g^-1, five times that of MIL-101(Fe). After photocatalytic experiments, MIL-101(Fe^II/Fe^III) retained an unchanged Fe^II/Fe^III rate, indicating that this Fe^II/Fe^III cycling can be maintained. DFT modeling of the Fe^II-rich MOF material showed that a FeII1 FeIII2 system has a higher N₂ activation capacity than a FeIII3 system. The catalytic mechanism was further proved by in situ infrared spectra and N¹⁵ isotopic tracers. Therefore, the improvement of photocatalytic activity was mainly attributed to the change in the nitrogen adsorption capacity during the photoinduced Fe^II/Fe^III cycling.

High-Efficiency Ammonia Electrosynthesis on Anatase TiO2-x Nanobelt Arrays with Oxygen Vacancies by Selective Reduction of Nitrite

Electrocatalytic reduction of nitrite to NH₃ provides a new route for the treatment of nitrite in wastewater, as well as an attractive alternative to NH₃ synthesis. Here, we report that an oxygen vacancy-rich TiO_2-x nanoarray with different crystal structures self-supported on the Ti plate can be prepared by hydrothermal synthesis and by subsequently annealing it in an Ar/H₂ atmosphere. Anatase TiO_2-x (A-TiO_2-x) can be a superb catalyst for the efficient conversion of NO₂^- to NH₃; a high NH₃ yield of 12,230.1 ± 406.9 μg h^-1 cm^-2 along with a Faradaic efficiency of 91.1 ± 5.5% can be achieved in a 0.1 M NaOH solution containing 0.1 M NaNO₂ at -0.8 V, which also exhibits preferable durability with almost no decay of catalytic performances after cycling tests and long-term electrolysis. Furthermore, a Zn-NO₂^- battery with such A-TiO_2-x as a cathode delivers a power density of 2.38 mW cm^-2 as well as a NH₃ yield of 885 μg h^-1 cm^-2.

Rare-Earth Single-Atom Catalysts: A New Frontier in Photo/Electrocatalysis

Single-atom catalysts (SACs) provide well-defined active sites with 100% atom utilization, and can be prepared using a wide range of support materials. Therefore, they are attracting global attention, especially in the fields of energy conversion and storage. To date, research has focused on transition-metal and precious-metal-based SACs. More recently, rare-earth (RE)-based SACs have emerged as a new frontier in photo/electrocatalysis owing to their unique electronic structure arising from the spin-orbit coupling of the 4f and valence orbitals, unsaturated coordination environment, and unique behavior as charge-transport bridges. However, a systematic review on the role of the RE active sites, catalytic mechanisms, and synthetic methods for RE SACs is lacking. Therefore, in this review, the latest developments in RE SACs having applications in photo/electrocatalysis are summarized and discussed. First, the theoretical advantages of RE SACs for photo/electrocatalysis are briefly introduced, focusing on the roles of the 4f orbitals and coupled energy levels. In addition, the most recent research progress on RE SACs is summarized for several important photo/electrocatalytic reactions and the corresponding catalytic mechanisms are discussed. Further, the synthetic strategies for the production of RE SACs are reported. Finally, challenges for the development of RE SACs are highlighted, along with future research directions and perspectives.

Enhancement of Plasmon-Induced Photoelectrocatalytic Water Oxidation over Au/TiO2 with Lithium Intercalation

Plasmon-induced chemical reaction is an emerging field but its development faces huge challenges because of low quantum efficiency. Herein, we report that the solar energy conversion efficiency of Au/TiO₂ in plasmon-induced water oxidation is greatly enhanced by intercalating Li⁺ into TiO₂ . An incident photon-to-current efficiency as high as 2.0 %@520 nm is achieved by Au/Li_0.2 TiO₂ in photoelectrocatalytic water oxidation, realizing a 33-fold enhancement in photocurrent density compared with Au/TiO₂ . The superior photoelectrocatalytic performance is mainly ascribed to the enhanced electric conductivity and higher catalytic activity of Li_0.2 TiO₂ . Furthermore, the ultrafast transient absorption spectroscopy suggests that lithium intercalation into TiO₂ could change the dynamics of hot electron relaxation in Au nanoparticles. This work demonstrates that intercalation of alkaline ions into semiconductors can promote the charge separation efficiency of the plasmonic effect of Au/TiO₂ .

Designing a Redox Heterojunction for Photocatalytic "Overall Nitrogen Fixation" under Mild Conditions

Ammonia and nitrates are the most fundamental and significant raw ingredients in human society. Till now, industrial synthetic ammonia by Haber-Bosch process and industrial synthetic nitrates by the Ostwald process have encountered increasingly serious challenges, i.e., high energy consumption, high cost, and environment-harmful gas emissions. Therefore, developing alternative approaches to achieve nitrogen fixation to overcome the inherent deficiencies of the well-established Haber-Bosch and Ostwald processes has fascinated scientists for many years, especially the simultaneous formation of ammonia and nitrate directly from N₂ molecules, which has been rarely studied. Herein, a heterojunction-based photocatalytic system is designed to successfully achieve "overall nitrogen fixation," a sustainable and simultaneous conversion of N₂ molecules into ammonia and nitrate products under mild conditions. In this heterojunction, interfacial charge redistribution (ICR) promotes selective accumulations of photogenerated electrons and holes in the CdS and WO₃ components. As a result, N₂ molecules can be activated and reduced to ammonia products with yields of 35.8 µmol h^-1 g^-1 by a multi-electron process, and synchronously oxidized into nitrate products with yields of 14.2 µmol h^-1 g^-1 by a hole-induced oxidation coupling process. This work provides a novel insight and promising approach to realize artificial nitrogen fixation under mild condition.

CdS and Ag synergistically improved the performance of g-C3N4 on visible-light photocatalytic degradation of pollution

CdS-AgO@g-C₃N₄ nanocomposites were successfully synthesized and characterized by XRD, N₂ physical adsorption, XPS, SEM, TEM, EDX, and UV-Vis DRS (various technical means). The adsorption light range of as-prepared materials could extend to the whole visible light region with the addition of Ag. Silver can act as a bridge to facilitate the separation of electrons and holes, thereby greatly enhancing the photocatalytic activity of CdS-AgO@g-C₃N₄, enabling the maximum degradation efficiency of salicylic acid in water to reach 92.8% under visible light. Peroxy radical is the most important radical in the photocatalytic reaction process, followed by electron and hole, while hydroxyl radical has almost no effect. In addition, the mechanism of photocatalytic process was also explored.

Regulating Electronic Structure in Bi2 O3 Architectures by Ti Mediation: A Strategy for Dual Active Sites Synergistically Promoting Photocatalytic Nitrogen Hydrogenation

Under mild conditions, nitrogen undergoes the associative pathways to be reduced with solar energy as the driving force for fixation, avoiding the high energy consumption when undergoing dissociation. Nevertheless, this process is hindered by the high hydrogenation energy barrier. Herein, Ti was introduced as hard acid into the δ-Bi₂ O₃ (Ti-Bi₂ O₃ ) lattice to tune its local electronic structure and optimize its photo-electrochemistry performance (reduced bandgap, increased conduction band maximum, and extended carrier lifetime). Heterokaryotic Ti-Bi dual-active sites in Ti-Bi₂ O₃ created a novel adsorption geometry of O-N₂ interaction proved by density functional theory calculation and N₂ temperature-programmed desorption. The synergistic effect of dual-active sites reduced the energy barrier of hydrogenation from 2.65 (Bi₂ O₃ ) to 2.13 eV (Ti-Bi₂ O₃ ), thanks to the highly overlapping orbitals with N₂ . Results showed that 10 % Ti-doped Bi₂ O₃ exhibited an excellent ammonia production rate of 508.6 μmol g_cat ^-1  h^-1 in water and without sacrificial agent, which is 4.4 times higher than that of Bi₂ O₃ . In this work, bridging oxygen activation and synergistic hydrogenation for nitrogen with Ti-Bi dual active sites may unveil a corner of the hidden nitrogen reduction reaction mechanism and serves as a distinctive strategy for the design of nitrogen fixation photocatalysts.

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.