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The electrochemical conversion of NOx (including NO3– and NO2–) to ammonium using renewable energy is emerging as a green alternative pathway for decarbonization of high emission industry to meet net zero emission targets. The key to efficient NOx electrolysis relies on the understanding of surface chemistry to establish the structure–activity relationships that will govern future scaleup of this process. In this work, we have undertaken a mechanistic investigation, wherein by tuning the surface oxidation state of CuOx nanoparticles on Cu foam (referred as CuOx/CuF), we are able to investigate its impact on conversion of NOx to ammonium (NH4+) under acidic reaction conditions. Supported by in situ Raman measurements, we reveal the importance of tuning the Cu oxidation state to maximize Cu2O formation, which forms beneficial Cu2O/Cu interfaces during reaction, allowing an enhanced NH4+ yield with a production rate of 45 nmol s–1 cm–2 and Faradaic efficiency (FENH4+) of 83% at −0.5 V vs RHE. Further, we reveal the promising stability of such interfaces under acidic conditions during long-term electrolysis for usage of up to 20 h. [ABSTRACT FROM AUTHOR]

Density functional theory calculations have used the local spin density approximation for characterizing triangle-shapes nanohole, nanodot and lattice antidote structures in hexagonal boron-nitride (h-BN) monolayer sheets. The studies have shown that despite lattice contraction due to the presence of multiple holes, antidote super lattices are predicted to be stable, displaying amplified magnetism as well as enhanced half-metallicity.

New Se (VI) and formic acid adsorption models were derived assuming that one Se (VI) ion is absorbed onto two active sites on the TiO (sub 2) surface and the competitive adsorption of both Se (VI) and formate ions. The use of these adsorption models enables the derivation of a rate equation on the basis of the (langmuit-hinshelwood) LH reaction mechanism.

Bioinspired nanotopography artificially fabricated on titanium surfaces offers a solution for the rising issue of postoperative infections within orthopedics. On a small scale, hydrothermal etching has proven to deliver an effective antimicrobial nanospike surface. However, translation to an industrial setting is limited by the elevated synthesis temperature (150 °C) and associated equipment requirements. Here, for the first time, we fabricate surface nanostructures using comparatively milder synthesis temperatures (75 °C), which deliver physicochemical properties and antimicrobial capability comparable to the high-temperature surface. Using a KOH etchant, the simultaneous formation of titania and titanate crystals at both temperatures produces a one-dimensional nanostructure array. Analysis indicated that the formation mechanism comprises dissolution and reprecipitation processes, identifying the deposited titanates as hydrated layered tetra-titanates (K 2 Ti 4 O 9 · n H 2 O). A proposed nanospike formation mechanism was confirmed through the identification of a core and outer shell for individual nanostructures, primarily comprised of titanates and titania, respectively. Etching conditions dictated crystalline formation, favoring a thicker titanate core for nanorods under higher synthesis temperatures and etchant concentrations. A bactericidal investigation showed the efficacy against Gram-negative bacteria for a representative low-temperature nanosurface (34.4 ± 14.4%) was comparable to the higher temperature nanosurface (34.0 ± 17.0%), illustrating the potential of low-temperature hydrothermal synthesis. Our results provide valuable insight into the applicability of low-temperature etching protocols that are more favorable in large-scale manufacturing settings.

Single-atom catalysts (SACs) have shown potential for achieving an efficient electrochemical CO 2 reduction reaction (CO2RR) despite challenges in their synthesis. Here, Ag 2 S/Ag nanowires provide initial anchoring sites for Cu SACs (Cu/Ag 2 S/Ag), then Cu/Ag(S) was synthesized by an electrochemical treatment resulting in complete sulfur removal, i.e., Cu SACs on a defective Ag surface. The CO2RR Faradaic efficiency (FE CO2RR ) of Cu/Ag(S) reaches 93.0% at a CO2RR partial current density ( j CO2RR ) of 2.9 mA/cm 2 under -1.0 V vs RHE, which outperforms sulfur-removed Ag 2 S/Ag without Cu SACs (Ag(S), 78.5% FE CO2RR with 1.8 mA/cm 2 j CO2RR ). At -1.4 V vs RHE, both FE CO2RR and j CO2RR over Cu/Ag(S) reached 78.6% and 6.1 mA/cm 2 , which tripled those over Ag(S), respectively. As revealed by in situ and ex situ characterizations together with theoretical calculations, the interacted Cu SACs and their neighboring defective Ag surface increase microstrain and downshift the d-band center of Cu/Ag(S), thus lowering the energy barrier by ∼0.5 eV for *CO formation, which accounts for the improved CO2RR activity and selectivity toward related products such as CO and C 2+ products.

The large-scale deployment of proton-exchange membrane water electrolyzers for high-throughput sustainable hydrogen production requires transition from precious noble metal anode electrocatalysts to low-cost earth-abundant materials. However, such materials are commonly insufficiently stable and/or catalytically inactive at low pH, and positive potentials required to maintain high rates of the anodic oxygen evolution reaction (OER). To address this, we explore the effects of a dielectric nanoscale-thin layer, constituted of amorphous TiO 2 , on the stability and electrocatalytic activity of nanostructured OER anodes based on low-cost Co 3 O 4 . We demonstrate a direct correlation between the OER performance and the thickness of the atomic layer deposited TiO 2 layers. An optimal TiO 2 layer thickness of 4.4 nm enhances the anode lifetime by a factor of ca. 3, achieving 80 h of continuous electrolysis at pH near zero, while preserving high OER catalytic activity of the bare Co 3 O 4 surface. Thinner and thicker TiO 2 layers decrease the stability and activity, respectively. This is attributed to the pitting of the TiO 2 layer at the optimal thickness, which allows for access to the catalytically active Co 3 O 4 surface while stabilizing it against corrosion. These insights provide directions for the engineering of active and stable composite earth-abundant materials for acidic water splitting for high-throughput hydrogen production.

In this study, we propose a top-down approach for the controlled preparation of undercoordinated Ni-N x (Ni-hG) and Fe-N x (Fe-hG) catalysts within a holey graphene framework, for the electrochemical CO 2 reduction reaction (CO 2 RR) to synthesis gas (syngas). Through the heat treatment of commercial-grade nitrogen-doped graphene, we prepared a defective holey graphene, which was then used as a platform to incorporate undercoordinated single atoms via carbon defect restoration, confirmed by a range of characterization techniques. We reveal that these Ni-hG and Fe-hG catalysts can be combined in any proportion to produce a desired syngas ratio (1-10) across a wide potential range (-0.6 to -1.1 V vs RHE), required commercially for the Fischer-Tropsch (F-T) synthesis of liquid fuels and chemicals. These findings are in agreement with our density functional theory calculations, which reveal that CO selectivity increases with a reduction in N coordination with Ni, while unsaturated Fe-N x sites favor the hydrogen evolution reaction (HER). The potential of these catalysts for scale up is further demonstrated by the unchanged selectivity at elevated temperature and stability in a high-throughput gas diffusion electrolyzer, displaying a high-mass-normalized activity of 275 mA mg -1 at a cell voltage of 2.5 V. Our results provide valuable insights into the implementation of a simple top-down approach for fabricating active undercoordinated single atom catalysts for decarbonized syngas generation.

Metallic foams, with intrinsic catalytic properties, are critical for heterogeneous catalysis reactions and reactor designs. Market ready catalytic foams are costly and made of multimaterial coatings with large sub-millimeter open cells providing insufficient active surface area. Here we use the principle of nanometallurgy within liquid metals to prepare nanostructured catalytic metal foams using a low-cost alloy of bismuth and tin with sub-micrometer open cells. The eutectic bismuth and tin liquid metal alloy was processed into nanoparticles and blown into a tin and bismuth nanophase separated heterostructure in aqueous media at room temperature and using an indium brazing agent. The CO 2 electroconversion efficiency of the catalytic foam is presented with an impressive 82% conversion efficiency toward formates at high current density of -25 mA cm -2 (-1.2 V vs RHE). Nanometallurgical process applied to liquid metals will lead to exciting possibilities for expanding industrial and research accessibility of catalytic foams.

Controllable concomitant production of CO and H 2 (syngas) during electrochemical CO 2 reduction reactions (CO 2 RR) is expected to improve the commercial feasibility of the technology to mitigate CO 2 emissions as the generated syngas can be converted into useful chemicals using the commercial Fischer-Tropsch (FT) process. Herein, we demonstrate the ability of a Co single-atom-decorated N-doped graphitic carbon shell-encapsulated cobalt nanoparticle electrocatalyst (referred as Co@CoNC-900) to controllably produce syngas at low overpotentials during CO 2 RR. Through the engineering and modulation of dual active sites for CO 2 RR (modified carbon shell with encapsulated Co) and hydrogen evolution reaction (Co-N 4 moieties) within Co@CoNC by varying the annealing temperature, we are able to tune the H 2 : CO ratio from 1: 2 to 1: 1 to 3: 2 over a wide range of applied potentials (-0.5 V to -0.8 V versus reversible hydrogen electrode, RHE). This versatile control of H 2 : CO ratio in CO 2 RR reaction brings up significant opportunity of using CO 2 and H 2 O and renewable energy for producing a range of chemicals.

Silica has the potential to enhance the performance of ceria-zirconia as a support for the dry reforming of methane; however, controlling the integration of silica with the ceria-zirconia using flame spray pyrolysis (FSP) is a significant challenge. To address this challenge, an asymmetrically variable double-FSP (DFSP) system was established to control the SiO 2 interaction with Ce 0.7 Zr 0.3 O 2 . The engineered materials were then utilized as supports for Ni for the dry reforming of methane. Initially, silica formation during FSP synthesis was examined where it was revealed that, at a low precursor concentration (<1.5 M tetraethyl orthosilicate in xylenes), the physical characteristics of the silica varied differently in relation to what is typically encountered during FSP synthesis. Explicitly, on using a 0.5 M tetraethyl orthosilicate precursor, increasing the FSP feed rate provided an increase in the specific surface area from 217 m 2 /g at 3 mL/min to 363 m 2 /g at 7 mL/min. Adopting this knowledge on silica formation under these conditions, the asymmetrical DFSP system was then exploited to regulate the integration of ceria-zirconia with the silica. To restrict the silica from coating the particles during DFSP, the intersection distance along the silica flame was tuned from 18.5 to 28.5 cm, whereas the distance along the ceria-zirconia flame was fixed at 5 cm. It was found that at short intersection distances the ceria-zirconia provided sites for silica nucleation and growth, resulting in high surface-area silica encapsulating the ceria-zirconia. At large intersection distances, encapsulation of the ceria-zirconia by silica was suppressed. An enhanced oxygen storage capacity and basicity along with the small Ni sizes facilitated by the longer intersection distances produced the most selective catalyst for the dry reforming of methane.

The interface at the metal oxide-carbon hybrid heterojunction is the source to the well-known "synergistic effect" in catalysis. Understanding the structure-function properties is key for designing more advanced catalyst-support systems. Using a model Mn III -O x single-layer catalyst on carbon, we herein report a full elucidation to the catalytic synergism at the hybrid heterojunction in the oxygen reduction reaction (ORR). The successful fabrication of the single-layer catalyst from bottom-up is fully characterized by the X-ray absorption fine structure and high-resolution transmission electron microscopy. For oxygen electrocatalysis over this model hybrid heterostructure, our results, from both theory and experiment, show that the synergistic ORR truly undergoes a cooperated two-step electrocatalysis with catalytic promotion (Δ E onset = 60 mV) near the heterojunction and over the single-layer catalyst through an interfacial electronic interplay, rather than an abstruse transition towards a one-step dissociative pathway. Finally, we report a superior peroxide-reducing activity of 432.5 mA cm -2 mg (M) -1 over the Mn III -O x single-layer.

Unique CO 2 methanation catalysts comprising bimetallic Ni-Rh nanoalloy/3DOM LaAlO 3 have been successfully prepared via a poly(methyl methacrylate) microsphere colloidal crystal-templating route, followed by the in situ growth of Ni nanoparticles (NPs). Here, we show that unlike traditional Ni particles deposited on a perovskite support, the exsolution of Ni occurs on both the external and internal surface of the porous perovskite substrate, leading to a strong metal-support interaction. Owing to the exsolution of Ni and the formation of Ni-Rh nanoalloys, a 52% enhancement in the methanation turnover frequency was obtained over the Ni-Rh/3DOM LaAlO 3 [13.9 mol/(mol h)] compared to Rh/3DOM LaNi 0.08 Al 0.92 O 3 [9.16 mol/(mol h)] before reduction treatment. The results show that the low-temperature reducibility, rich surface adsorbed oxygen species, and basic sites of the catalyst greatly improve its activity toward CO 2 methanation. The hierarchically porous structure of the perovskite support provides a high dispersion of bimetallic Ni-Rh NPs.

It has been reported that photogenerated electrons and holes can be directed toward specific crystal facets of a semiconductor particle, which is believed to arise from the differences in their surface electronic structures, suggesting that different facets can act as either photoreduction or photo-oxidation sites. This study examines the propensity for this effect to occur in faceted, plate-like bismuth molybdate (Bi 2 MoO 6 ), which is a useful photocatalyst for water oxidation. Photoexcited electrons and holes are shown to be spatially separated toward the {100} and {001}/{010} facets of Bi 2 MoO 6 , respectively, by facet-dependent photodeposition of noble metals (Pt, Au, and Ag) and metal oxides (PbO 2 , MnO x , and CoO x ). Theoretical calculations revealed that differences in energy levels between the conduction bands and valence bands of the {100} and {001}/{010} facets can contribute to electrons and holes being drawn to different surfaces of the plate-like Bi 2 MoO 6 . Utilizing this knowledge, the photo-oxidative capability of Bi 2 MoO 6 was improved by adding an efficient water oxidation co-catalyst, CoO x , to the system, whereby the extent of enhancement was shown to be governed by the co-catalyst location. A greater oxygen evolution occurred when CoO x was selectively deposited on the hole-rich {001}/{010} facets of Bi 2 MoO 6 compared to when CoO x was randomly located across all of the facets. The elevated performance exhibited for the selectively loaded CoO x /Bi 2 MoO 6 was ascribed to the greater opportunity for hole trapping by the co-catalyst being accentuated over other potentially detrimental effects, such as the co-catalyst acting as a recombination medium and/or covering reactive sites. The results indicate that harnessing the synergy between the spatial charge separation and the co-catalyst location on the appropriate facets of plate-like Bi 2 MoO 6 can promote its photocatalytic activity.

Au nanoparticles with different sizes (10, 20, 30, and 50 nm) were synthesized using a seed-assisted approach and anchored onto Pt/TiO 2 employing 3-mercaptopropionic acid as the organic linker. The sizes of the Au nanoparticles were controlled within a narrow range so that the size-dependent surface plasmonic resonance effect on sensitizing Pt/TiO 2 can be thoroughly studied. We found that 20 nm Au nanoparticles (Au 20 ) gave the best performance in sensitizing Pt/TiO 2 to generate H 2 under visible-light illumination. Photoelectrochemical measurements indicated that Au 20 -Pt/TiO 2 exhibited the most efficient "hot" electrons separation among the studied catalysts, correlating well with the photocatalytic activity. The superior performance of Au-supported Pt/TiO 2 (Au 20 -Pt/TiO 2 ) compared with Au anchored to TiO 2 (Au 20 /TiO 2 ) revealed the important role of Pt as a cocatalyst for proton reduction. To elucidate how the visible-light excited hot electrons in Au nanoparticles involved in the proton-reduction reaction process, Au 20 /TiO 2 was irradiated by visible light (λ > 420 nm) with the presence of Pt precursor (H 2 PtCl 6 ) in a methanol aqueous solution under deaerated condition. Energy-dispersive X-ray spectroscopy mapping analysis on the recovered sample showed that Pt ions could be reduced on the surfaces of both Au nanoparticles and TiO 2 support. This observation indicated that the generated hot electrons on Au nanoparticles were injected into the TiO 2 conduction band, which were then subsequently transferred to Pt nanoparticles where proton reduction proceeded. Besides, the excited hot electrons could also participate in the proton reduction on Au nanoparticles surface.