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Cu is a unique metal that catalyzes carbon monoxide/carbon dioxide (CO/CO2) to form high-order hydrocarbons and oxygenates through the CO/CO2 reduction reaction (CO/CO2RR) at decent selectivity and productivity.

Here, we report a facile approach for synthesizing M–N–C catalysts (M = Co, Fe, Ni) at a commercial scale without employing organic solvents. Our characterization efforts indicate that single atomic catalysts with high surface areas were successfully obtained. Electrochemical measurements demonstrate that, among the three synthesized catalysts, Ni–N–C exhibits the highest performance in the electrochemical CO2 reduction reaction (CO2RR) to carbon monoxide (CO), affording 80% Faradaic efficiency (FE) of CO production at –0.49 VRHE with a turnover frequency (TOF) of 57,379 h–1. Large-scale synthesis coupled with high performance allows moving forward with the practical implementation of M–N–C catalysts for industrially relevant CO2RR.

Amorphous alumina overcoats generated by atomic layer deposition (ALD) have been shown to improve the selectivity and durability of supported metal catalysts in many reactions. Several mechanisms have been proposed to explain the enhanced catalytic performance, but the accessibilities of reactants through the amorphous overcoats remain elusive, which is crucial for understanding reaction mechanisms. Here, we show that an AlO

We report a strategy to integrate atomically dispersed iron within a heterogeneous nitrogen-doped carbon (N-C) support, inspired by routes for metalation of molecular macrocyclic iron complexes. The N-C support, derived from pyrolysis of a ZIF-8 metal-organic framework, is metalated via solution-phase reaction with FeCl(2) and tributyl amine, as a Brønsted base, at 150 °C. Fe active sites are characterized by (57)Fe Mössbauer spectroscopy and aberration-corrected scanning transmission electron microscopy. The site density can be increased by selective removal of Zn(2+) ions from the N-C support prior to metalation, resembling the transmetalation strategy commonly employed for the preparation of molecular Fe-macrocycles. The utility of this approach is validated by the higher catalytic rates (per total Fe) of these materials relative to established Fe-N-C catalysts, benchmarked using an aerobic oxidation reaction.

Nanoparticles are an important class of materials that exhibit special properties arising from their high surface area-to-volume ratio. Scanning transmission electron microscopy (STEM) has played an important role in nanoparticle characterization, owing to its high spatial resolution, which allows direct visualization of composition and morphology with atomic precision. This typically comes at the cost of sample size, potentially limiting the accuracy and relevance of STEM results, as well as the ability to meaningfully track changes in properties that vary spatially. In this work, automated STEM data acquisition and analysis techniques are employed that enable physical and compositional properties of nanoparticles to be obtained at high resolution over length scales on the order of microns. This is demonstrated by studying the localized effects of potential cycling on electrocatalyst degradation across proton exchange membrane fuel cell cathodes. In contrast to conventional, manual STEM measurements, which produce particle size distributions representing hundreds of particles, these high-throughput automated methods capture tens of thousands of particles and enable nanoparticle size, number density, and composition to be measured as a function of position within the cathode. Comparing the properties of pristine and degraded fuel cells provides statistically robust evidence for the inhomogeneous nature of catalyst degradation across electrodes. These results demonstrate how high-throughput automated STEM techniques can be utilized to investigate local phenomena occurring in nanoparticle systems employed in practical devices.

Carbon supported and nitrogen coordinated single Mn site (Mn-N-C) catalysts are the most desirable platinum group metal (PGM)-free cathode catalysts for proton-exchange membrane fuel cells (PEMFCs) due to their insignificant Fenton reactions (vs. Fe), earth abundances (vs. Co), and encouraging activity and stability. However, current Mn-N-C catalysts suffer from high overpotential due to low intrinsic activity and less dense MnN4 sites. Herein, we present a sulfur-doped Mn-N-C catalyst (Mn-N-C-S) synthesized through an effective adsorption-pyrolysis process. Using electron microscopy and X-ray absorption spectroscopy (XAS) techniques, we verify the uniform dispersion of MnN4 sites and confirm the effect of S doping on the Mn-N coordination. The Mn-N-C-S catalyst exhibits a favorable oxygen reduction reaction (ORR) activity in acidic media relative to the S-free Mn-N-C catalyst. The corresponding membrane electrode assembly (MEA) generates enhanced performance with a peak power density of 500 mW cm-2 under a realistic H2/air environment. The constant voltage tests of fuel cells confirm the much-enhanced stability of the Mn-N-C-S catalyst compared to the Fe-N-C and Fe-N-C-S catalysts. The electron microscopy and Fourier transform XAS analyses provide insights into catalyst degradation associated with Mn oxidation and agglomeration. The theoretical calculation elucidates that the promoted ORR activity is mainly attributed to the spatial effect stemmed from the repulsive interaction between the ORR intermediates and adjacent S dopants.

We elucidate the structural evolution of CoN4 sites during thermal activation by developing a zeolitic imidazolate framework (ZIF)-8-derived carbon host as an ideal model for Co2+ ion adsorption. Subsequent in situ X-ray absorption spectroscopy analysis can dynamically track the conversion from inactive Co-OH and Co-O species into active CoN4 sites. The critical transition occurs at 700 °C and becomes optimal at 900 °C, generating the highest intrinsic activity and four-electron selectivity for the oxygen reduction reaction (ORR). DFT calculations elucidate that the ORR is kinetically favored by the thermal-induced compressive strain of Co-N bonds in CoN4 active sites formed at 900 °C. Further, we developed a two-step (i.e., Co ion doping and adsorption) Co-N-C catalyst with increased CoN4 site density and optimized porosity for mass transport, and demonstrated its outstanding fuel cell performance and durability.

Modulation of bimetallic nanocatalysts with atomic precision would allow for significant increases in catalyst activity through the optimization of heteroatomic interplay. In practice, this level o...

Commercial proton exchange membrane heavy-duty fuel cell vehicles will require a five-fold increase in durability compared to current state-of-the art light-duty fuel cell vehicles. We describe a new composite membrane that incorporates silicotungstic heteroply acid (HPA), α-K8SiW11O40▪13H2O, a radical decomposition catalyst and when acid-exchanged can potentially conduct protons. The HPA was covalently bound to a terpolymer of tetrafluoroethylene, vinylidene fluoride, and sulfonyl fluoride containing monomer (1,1,2,2,3,3,4,4-octafluoro-4-((1,2,2-trifluorovinyl)oxy)butane-1-sulfonyl fluoride) by dehydrofluorination followed by addition of diethyl (4-hydroxyphenyl) phosphonate, giving a perfluorosulfonic acid-vinylidene fluoride-heteropoly acid (PFSA-VDF-HPA). A composite membrane was fabricated using a blend of the PFSA-VDF-HPA and the 800EW 3M perfluoro sulfonic acid polymer. The bottom liner-side of the membrane tended to have a higher proportion of HPA moieties compared to the air-side as gravity caused the higher mass density PFSA-VDF-HPA to settle. The composite membrane was shown to have less swelling, more hydrophobic properties, and higher crystallinity than the pure PFSA membrane. The proton conductivity of the membrane was 0.130 ± 0.03 S cm−1 at 80 °C and 95% RH. Impressively, when the membrane with HPA-rich side was facing the anode, the membrane survived more than 800 h under accelerated stress test conditions of open-circuit voltage, 90 °C and 30% RH.

MEAs with nanofiber mat electrodes containing Pt/C catalyst and Nafion binder were fabricated and evaluated. The electrodes were prepared by electrospinning a solution of catalyst powder, salt-form Nafion (with Na+, Li+, or Cs+ as the sulfonic acid counterion), and a carrier polymer of either polyethylene oxide or poly(acrylic acid). The carrier polymer was extracted prior to MEA testing by a hot water soaking step. The resulting fibers were 15%–17% porous, with a core–shell-like morphology (a coating of primarily Nafion on the fiber surface). MEAs with anode/cathode catalyst loadings of 0.1 mgPt cm−2 each and a Nafion 211 membrane produced high power at both high and low relative humidity (RH) conditions in H2/air fuel cell tests, e.g., a maximum power density of 919 mW cm−2 at 100% RH and 832 mW cm−2 at 40% RH for a test at 80 °C and 200 kPaabs. The presence of nm-size pores within the fibers trapped water via capillary condensation during low RH feed gas testing, thus maintaining a high proton conductivity of the Nafion binder in the anode and cathode while minimizing/eliminating ionic isolation of catalyst particles in low water content, poorly conductive binder.

Silicon has several technologically promising allotropes that are formed via high-pressure synthesis. One of these phases (hd) has been predicted to have a direct band gap under tensile strain, whereas other (r8 and bc8) phases are predicted to have narrow band gaps and good absorption across the solar spectrum. Pure volumes of these phases cannot be made using conventional nanowire growth techniques. In this work, Si nanowires were compressed up to ∼20 GPa and then decompressed using a diamond anvil cell in the temperature range of 25-165 °C. It was found that at intermediate temperatures, near-phase-pure bc8-Si nanowires were produced, whereas amorphous Si (a-Si) dominated at lower temperatures, and a direct transformation to the diamond cubic phase (dc-Si) occurred at higher temperatures under compression. Thus this study has opened up a new pressure-temperature pathway for the synthesis of novel Si nanowires consisting of designed phase components with transformative properties.

The development of targeted alpha therapy (TAT) as a viable cancer treatment requires innovative solutions to challenges associated with radionuclide retention to enhance local tumor cytotoxicity and to minimize off-target effects. Nanoparticles (NPs) with high encapsulation and high retention of radionuclides have shown potential in overcoming these issues. This article shows the influence of pH on the structure of lanthanum vanadate (LaVO4) NPs and its impact on the radiochemical yield of 223Ra and subsequent retention of its decay daughters, 211Pb and 211Bi. An acidic pH (4.9) results in a high fraction of La(223Ra)VO4 NPs with tetragonal structure (44.6&ndash, 66.1%) and a 223Ra radiochemical yield &lt, 40%. Adjusting the pH to 11 yields &gt, 80% of La(223Ra)VO4 NPs with monoclinic structure and increases the 223Ra radiochemical yield &gt, 85%. The leakage of decay daughters from La(223Ra)VO4 NPs (pH 11) was &lt, 5% and &lt, 0.5% when exposed to deionized water and phosphate-buffered saline, respectively. Altering the surface chemistry of La(223Ra)VO4 NPs with carboxylate and phosphate compounds resulted in a threefold decrease in hydrodynamic diameter and a 223Ra radiochemical yield between 74.7% and 99.6%. These results show the importance of tailoring the synthesis parameters and surface chemistry of LaVO4 NPs to obtain high encapsulation and retention of radionuclides.

Sulfur and coking tolerance of Ni-based dry reforming catalysts were examined. Catalysts utilizing both Ce/Zr and Ce/La oxide supports, some with additional Co, were tested. Long-term reaction runs were conducted with and without sulfur in the feed. Catalysts were also characterized by STEM, XPS, XAFS and XANES and CO chemisorption. Only catalysts where Co was also present, and supported on the Ce-Zr oxide, were capable of extended sulfur tolerance at >20 ppm sulfur. This tolerance, along with a greatly reduced coking rate, is linked to Co in intimate contact with Ni, the mixture existing as clusters anchored and influenced electronically by the oxide support. The activation of methane takes place on these sites. Larger metal aggregates formed by ripening during reaction appear to be spectators. The measured activation energies for dry reforming suggest that CO2 activation takes place at the oxide interface, and is a kinetically significant step.

Atomically dispersed FeN4 active sites have exhibited exceptional catalytic activity and selectivity for the electrochemical CO2 reduction reaction (CO2RR) to CO. However, the understanding behind the intrinsic and morphological factors contributing to the catalytic properties of FeN4 sites is still lacking. By using a Fe-N-C model catalyst derived from the ZIF-8, we deconvoluted three key morphological and structural elements of FeN4 sites, including particle sizes of catalysts, Fe content, and Fe-N bond structures. Their respective impacts on the CO2RR were comprehensively elucidated. Engineering the particle size and Fe doping is critical to control extrinsic morphological factors of FeN4 sites for optimal porosity, electrochemically active surface areas, and the graphitization of the carbon support. In contrast, the intrinsic activity of FeN4 sites was only tunable by varying thermal activation temperatures during the formation of FeN4 sites, which impacted the length of the Fe-N bonds and the local strains. The structural evolution of Fe-N bonds was examined at the atomic level. First-principles calculations further elucidated the origin of intrinsic activity improvement associated with the optimal local strain of the Fe-N bond.

Electrochemical CO2 reduction is a potential approach to convert CO2 into valuable chemicals using electricity as feedstock. Abundant and affordable catalyst materials are needed to upscale this process in a sustainable manner. Nickel-nitrogen-doped carbon (Ni-N-C) is an efficient catalyst for CO2 electro-reduction to CO, and the single-site Ni-Nx motif is believed as the active site. However, critical metrics for its catalytic activity, such as active site density and intrinsic turnover frequency, so far lack systematic discussion. In this work, we prepared a set of covalent organic framework (COF)-derived Ni-N-C catalysts, for which the Ni-Nx content could be adjusted by the pyrolysis temperature. The combination of high-angle annular dark-field scanning transmission electron microscopy and extended X-ray absorption fine structure evidenced the presence of Ni single-sites, and quantitative X-ray photoemission addressed the relation between active site density and turnover frequency.

Atomically dispersed and nitrogen coordinated single metal sites (M-N-C, M=Fe, Co, Ni, or Mn) are the popular platinum group-metal (PGM)-free catalysts for many electrochemical reactions. Traditional wet-chemistry catalyst synthesis often requires complex procedures with unsatisfied reproducibility and scalability. Here, we report a chemical vapor deposition (CVD) strategy to synthesize the promising single metal site (M-N-C) catalysts. The deposition of gaseous 2-methylimidazole onto ZnO substrates doped with M, followed by an in-situ thermal activation, was proved effective in generating single metal sites well dispersed into porous carbon. In particular, an optimal CVD-derived Fe-N-C catalyst is featured with atomically dispersed FeN4 sites with increased Fe loading relative to other catalysts from wet-chemistry synthesis. The catalyst exhibited outstanding oxygen-reduction activity in acidic electrolytes, which was further studied in proton-exchange membrane fuel cells with encouraging performance. The CVD synthesis sheds some light on the mass production of single metal site catalysts towards advanced electrocatalysis.

Cost and durability remain the two major barriers to the widespread commercialization of polymer electrolyte membrane fuel cell (PEMFC)-based power systems, especially for the most impactful but challenging fuel cell electric vehicle (FCEV) application. Commercial FCEVs are now on the road; however, their PEMFC systems do not meet the cost targets established by the U.S. Department of Energy, primarily due to the high platinum loading needed on the cathode to achieve the requisite performance and lifetime. While the activities of a number of commercial Pt-based alloy cathode catalysts exceed the beginning-of-life (BOL) targets, these activities, and the overall cathode performance, degrade via a variety of mechanisms described herein. Degradation is mitigated in current FCEVs by utilizing a cathode catalyst with a lower BOL activity (e.g., much lower transition metal alloy content and larger BOL nanoparticle size), necessitating higher catalyst loadings, and through the utilization of system controls that avoid conditions known to exacerbate degradation processes, such as limiting the fuel cell stack voltage range. The design and development of active and robust materials and eliminating the need for vehicle mitigation strategies would greatly simplify the operating system, allowing for greater transient operation, avoiding large hybridization, and curtailing of fuel cell power. Although system mitigation strategies have provided the near-term pathway for FCEV commercialization, material-specific solutions are required to further reduce costs and improve operability and efficiency. Future material developments should focus on stabilization of the electrode structure and minimization of the catalyst particle susceptibility to dissolution caused by oxide formation and reduction over PEMFC cathode-relevant operating potentials plus minimization of support corrosion. Ex situ accelerated stress tests have provided insight into the processes responsible for material and performance degradation and will continue to provide useful information on the relative stability of materials and benchmarks for robust and stable materials-based solutions not requiring system mitigation strategies to achieve adequate lifetime.

The valence change model describes the resistive switching in metal oxide-based devices as due to electroreduction of the oxide and subsequent electromigration of oxygen vacancies. Here, we present cross-sectional X-ray energy-dispersive spectroscopy elemental maps of Ta, O, N, and Ti in electroformed TiN/TaO₂.₀/TiN structures. O, N, and Ti were exchanged between the anode and the functional oxide in devices formed at high power (∼1 mW), but the exchange was below the detection limit at low power (

Many important chemical transformations enabled by plasmonic hot carrier photocatalysis have been reported, although their efficiencies are often too low for practical applications. We examine how the efficiency of plasmon-induced hot electron transfer depends on the Au particle size in Au-tipped CdS nanorods. We show that with decreasing Au size, the plasmon width increases due to enhanced surface damping contributions. The excitation of Au nanoparticles leads to an instrument response time-limited ultrafast hot electron transfer process to CdS (≪140 fs). The quantum efficiency of this process increases from ∼1% to ∼18% as the particle size decreases from 5.5 ± 1.1 to 1.6 ± 0.5 nm due to both enhanced hot electron generation and transfer efficiencies in small Au particles. Our finding suggests that decreasing plasmonic particle size is an effective approach for improving plasmon-induced hot carrier transfer efficiency and provides important insight for the rational improvement of plasmonic hot carrier-based devices.

Synthetic strategies for the improvement in electronic conductivities and electrochemical stabilities of transition metal oxide cathodes, which are limiting factors in the performance of commercial...

CeO2–ZrO2 (CZO) nanoparticles (NPs) have applications in many catalytic reactions, such as methane dry reforming, due to their oxygen cycling ability. Ni doping has been shown to improve the cataly...

Here, we demonstrate the theory-guided plasma synthesis of high purity nanocrystalline Li3.5Si0.5P0.5O4 and fully amorphous Li2.7Si0.7P0.3O3.17N0.22. The synthesis involves the injection of single ...

Colloidal metal nanoparticles (NPs) have long been regarded as ideal precursors for the synthesis of well-defined supported metal catalysts. However, the integration of colloidal metal NPs and cata...

Proton-exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) are promising power sources from portable electronic devices to vehicles. The high-cost issue of these low-temperature fuel cells can be primarily addressed by using platinum-group metal (PGM)-free oxygen reduction reaction (ORR) catalysts, in particular atomically dispersed metal–nitrogen–carbon (M–N–C, M = Fe, Co, Mn). Furthermore, a significant advantage of M–N–C catalysts is their superior methanol tolerance over Pt, which can mitigate the methanol cross-over effect and offer great potential of using a higher concentration of methanol in DMFCs. Here, we investigated the ORR catalytic properties of M–N–C catalysts in methanol-containing acidic electrolytes via experiments and density functional theory (DFT) calculations. FeN4 sites demonstrated the highest methanol tolerance ability when compared to metal-free pyridinic N, CoN4, and MnN4 active sites. The methanol adsorption on MN4 sites is even strengthened when electrode potentials are applied during the ORR. The negative influence of methanol adsorption becomes significant for methanol concentrations higher than 2.0 M. However, the methanol adsorption does not affect the 4e− ORR pathway or chemically destroy the FeN4 sites. The understanding of the methanol-induced ORR activity loss guides the design of promising M–N–C cathode catalyst in DMFCs. Accordingly, we developed a dual-metal site Fe/Co–N–C catalyst through a combined chemical-doping and adsorption strategy. Instead of generating a possible synergistic effect, the introduced Co atoms in the first doping step act as “scissors” for Zn removal in metal–organic frameworks (MOFs), which is crucial for modifying the porosity of the catalyst and providing more defects for stabilizing the active FeN4 sites generated in the second adsorption step. The Fe/Co–N–C catalyst significantly improved the ORR catalytic activity and delivered remarkably enhanced peak power densities (i.e., 502 and 135 mW cm−2) under H2–air and methanol–air conditions, respectively, representing the best performance for both types of fuel cells. Notably, the fundamental understanding of methanol tolerance, along with the encouraging DMFC performance, will open an avenue for the potential application of atomically dispersed M–N–C catalysts in other direct alcohol or ammonia fuel cells.

Nanoscale multi-principal element intermetallics (MPEIs) may provide a broad and tunable compositional space of active, high–surface area materials with potential applications such as catalysis and magnetics. However, MPEI nanoparticles are challenging to fabricate because of the tendency of the particles to grow/agglomerate or phase-separated during annealing. Here, we demonstrate a disorder-to-order phase transition approach that enables the synthesis of ultrasmall (4 to 5 nm) and stable MPEI nanoparticles (up to eight elements). We apply just 5 min of Joule heating to promote the phase transition of the nanoparticles into L1 0 intermetallic structure, which is then preserved by rapidly cooling. This disorder-to-order transition results in phase-stable nanoscale MPEIs with compositions (e.g., PtPdAuFeCoNiCuSn), which have not been previously attained by traditional synthetic methods. This synthesis strategy offers a new paradigm for developing previously unexplored MPEI nanoparticles by accessing a nanoscale-size regime and novel compositions with potentially broad applications.

Aerogels are fascinating materials that can be used for a wide range of applications, one of which is electrocatalysis of the important oxygen reduction reaction. In their inorganic form, aerogels can have ultrahigh catalytic site density, high surface area, and tunable physical properties and chemical structures-important features in heterogeneous catalysis. Herein, we report on the synthesis and electrocatalytic properties of an iron-porphyrin aerogel. 5,10,15,20-(Tetra-4-aminophenyl)porphyrin (H2 TAPP) and FeII were used as building blocks of the aerogel, which was later heat-treated at 600 °C to enhance electronic conductivity and catalytic activity, while preserving its macrostructure. The resulting material has a very high concentration of atomically dispersed catalytic sites (9.7×1020 sites g-1 ) capable of catalyzing the oxygen reduction reaction in alkaline solution (Eonset =0.92 V vs. RHE, TOF=0.25 e- site-1 s-1 at 0.80 V vs. RHE).