Prospects of Platinum-Based Nanostructures for the Electrocatalytic Reduction of Oxygen

Surface coverage and reconstruction analyses bridge the correlation between structure and activity for electrocatalysis

Electrocatalysis is key to realizing a sustainable future for our society. However, the complex interface between electrocatalysts and electrolytes presents an ongoing challenge in electrocatalysis, hindering the accurate identification of effective/authentic structure-activity relationships and determination of favourable reaction mechanisms. Surface coverage and reconstruction analyses of electrocatalysts are important to address each conjecture and/or conflicting viewpoint on surface-active phases and their corresponding electrocatalytic origin, i.e., so-called structure-activity relationships. In this review, we emphasize the importance of surface states in electrocatalysis experimentally and theoretically, providing guidelines for research practices in discovering promising electrocatalysts. Then, we summarize some recent progress of how surface states determine the adsorption strengths and reaction mechanisms of occurring electrocatalytic reactions, exemplified in the electrochemical oxygen evolution reaction, oxygen reduction reaction, nitrogen reduction reaction, CO2 reduction reaction, CO2 and N2 co-reductions, and hydrogen evolution reaction. Finally, the review proposes deep insights into the in situ study of surface states, their efficient building and the application of surface Pourbaix diagrams. This review will accelerate the development of electrocatalysts and electrocatalysis theory by arousing broad consensus on the significance of surface states.

Strain Engineering of Unconventional Crystal-Phase Noble Metal Nanocatalysts

The crystal phase, alongside the composition, morphology, architecture, facet, size, and dimensionality, has been recognized as a critical factor influencing the properties of noble metal nanomaterials in various applications. In particular, unconventional crystal phases can potentially enable fascinating properties in noble metal nanomaterials. Recent years have witnessed notable advances in the phase engineering of nanomaterials (PEN). Within the accessible strategies for phase engineering, the effect of strain cannot be ignored because strain can act not only as the driving force of phase transition but also as the origin of the diverse physicochemical properties of the unconventional crystal phase. In this review, we highlight the development of unconventional crystal-phase noble metal nanomaterials within strain engineering. We begin with a short introduction of the unconventional crystal phase and strain effect in noble metal nanomaterials. Next, the correlations of the structure and performance of strain-engineered unconventional crystal-phase noble metal nanomaterials in electrocatalysis are highlighted, as well as the phase transitions of noble metal nanomaterials induced by the strain effect. Lastly, the challenges and opportunities within this rapidly developing field (i.e., the strain engineering of unconventional crystal-phase noble metal nanocatalysts) are discussed.

Enhanced Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol over Silica-Coated Pt-CoxOy Hybrid Nanoparticles

Selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) is difficult due to the intrinsic difficulty with thermodynamically easier hydrogenation of C═C bonds. In this work, Pt-CoxOy hybrid nanoparticles encapsulated in mesoporous silica nanospheres (Pt-CoxOy@mSiO2) were synthesized by a sol-gel method, which showed greatly improved COL selectivity for hydrogenation of CAL. At 80 °C and 1.0 MPa of H2, Pt-CoxOy@mSiO2 achieved a CAL conversion of 98.7% with a COL selectivity of 93.5%. In contrast, Pt@mSiO2 yields 3-phenylpropanol (HCOL) as the major product with HCOL selectivity of 67.2%, while PtCo@mSiO2 yields 3-phenylpropionaldehyde with selectivity of 51.8% under the same conditions. The enhanced catalytic performance of Pt-CoxOy@mSiO2 for hydrogenation of CAL to COL is ascribed to the Pt surface electron deficiency induced by metal-oxide interaction, and the protection of active NPs by silica shells results in good catalytic stability.

Bubble-Mediated Large-Scale Hierarchical Assembly of Ultrathin Pt Nanowire Network Monolayer at Gas/Liquid Interfaces

Extensive macroscale two-dimensional (2-D) platinum (Pt) nanowire network (NWN) sheets are created through a hierarchical self-assembly process with the aid of biomolecular ligands. The Pt NWN sheet is assembled from the attachment growth of 1.9 nm-sized 0-D nanocrystals into 1-D nanowires featuring a high density of grain boundaries, which then interconnect to form monolayer network structures extending into centimeter-scale size. Further investigation into the formation mechanism reveals that the initial emergence of NWN sheets occurs at the gas/liquid interfaces of the bubbles produced by sodium borohydride (NaBH₄) during the synthesis process. Upon the rupture of these bubbles, an exocytosis-like process releases the Pt NWN sheets at the gas/liquid surface, which subsequently merge into a continuous monolayer Pt NWN sheet. The Pt NWN sheets exhibit outstanding oxygen reduction reaction (ORR) activities, with specific and mass activities 12.0 times and 21.2 times greater, respectively, than those of current state-of-the-art commercial Pt/C electrocatalysts.

Atomic Scaled Depth Correlation to the Oxygen Reduction Reaction Performance of Single Atom Ni Alloy to the NiO2 Supported Pd Nanocrystal

This study demonstrates the intercalation of single-atom Ni (NiSA ) substantially reduces the reaction activity of Ni oxide supported Pd nanoparticle (NiO2 /Pd) in the oxygen reduction reaction (ORR). The results indicate the transition states kinetically consolidate the adsorption energy for the chemisorbed O and OH species on the ORR activity. Notably, the NiO2 /Ni1 /Pd performs the optimum ORR behavior with the lowest barrier of 0.49 eV and moderate second-step barrier of 0.30 eV consequently confirming its utmost ORR performance. Through the stepwise cross-level demonstrations, a structure-Eads -ΔE correspondence for the proposed NiO2 /Nin /Pd systems is established. Most importantly, such a correspondence reveals that the electronic structure of heterogeneous catalysts can be significantly differed by the segregation of atomic clusters in different dimensions and locations. Besides, the doping-depth effect exploration of the NiSA in the NiO2 /Pd structure intrinsically elucidates that the Ni atom doping in the subsurface induces the most fruitful NiSA /PdML synergy combining the electronic and strain effects to optimize the ORR, whereas this desired synergy diminishes at high Pd coverages. Overall, the results not only rationalize the variation in the redox properties but most importantly provides a precision evaluation of the process window for optimizing the configuration and composition of bimetallic catalysts in practical experiments.

Pd-In intermetallic nanoparticles with high catalytic selectivity for liquid-phase semi-hydrogenation of diphenylacetylene

Intermetallic nanoparticles (NPs) are highly interesting materials in catalysis due to their geometrically ordered structures and altered electronic properties, but the synthesis of defined intermetallic NPs remains a challenge. Here, we report a novel and facile approach for the synthesis of intermetallic Pd-In NPs in ionic liquids (ILs) at moderate temperatures. Depending on the molar ratio of the metal precursors and the reaction temperature, single-phase Pd₃In, PdIn and Pd₃In₇ NPs were obtained, which was confirmed, e.g. by powder X-ray diffraction, electron microscopy, and optical emission spectroscopy with inductively coupled plasma. The Pd-In NPs stabilized in ILs were used as catalysts in the liquid-phase semi-hydrogenation of diphenylacetylene (DPA). Highly ordered PdIn NPs with a CsCl type structure revealed both high activity and selectivity to cis-stilbene even at full DPA conversion. Intermetallic compounds such as PdIn can be used to isolate contiguous Pd atoms with another base metal into single Pd sites, thereby increasing the catalytic selectivity of Pd while stabilizing the individual sites in the intermetallic structures. This work may provide new pathways for the synthesis of single-phase intermetallic NPs and future insights into a more rational design of bimetallic catalysts with specific catalytic properties.

Low-Loading Sub-3 nm PtCo Nanoparticles Supported on Co-N-C with Dual Effect for Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells

Developing low-loading Pt-based catalysts possessing glorious catalytic performance can accelerate oxygen reduction reaction (ORR) and hence significantly advance the commercialization of proton exchange membrane fuel cells. In this report, we propose a hybrid catalyst that consists of low-loading sub-3 nm PtCo intermetallic nanoparticles carried on Co-N-C (PtCo/Co-N-C) via the microwave-assisted polyol procedure and subsequent heat treatment. Atomically dispersed Co atoms embedded in the Co-N-C carriers diffuse into the lattice of Pt, thus forming ultrasmall PtCo intermetallic nanoparticles. Owing to the dual effect of the enhanced metal-support interaction and alloy effect, as-fabricated PtCo/Co-N-C catalysts deliver an extraordinary performance, achieving a half-wave potential of 0.921 V, a mass activity of 0.700 A mg_Pt^-1@0.9 V, and brilliant durability in the acidic medium. The fuel cell employing PtCo/Co-N-C as the cathode catalyst with an ultralow Pt loading of 0.05 mg cm^-2 exhibits an impressive peak power density of 0.700 W cm^-2, higher than that of commercial Pt/C under the same condition. Furthermore, the enhanced intrinsic ORR activity and stability are imputed to the downshifted d-band center and the strengthened metal-support interaction, as revealed by density functional theory calculations. This report affords a facile tactic to fabricate Pt-based alloy composite catalysts, which is also applicable to other alloy catalysts.

Colorimetric Sensor Based on Ag-Fe NTs for H2S Sensing

Meat waste is widely associated with spoilage caused by microbial growth and metabolism. Volatile compounds produced by microbial growth such as volatile sulfides could directly indicate the freshness of meat during distribution and storage. Herein, silver-iron nanotriangles (Ag-Fe NTs) for hydrogen sulfide (H₂S) detection were developed via one-pot facile reflux reactions. The Ag-Fe NTs were integrated into food packaging systems for the rapid, real-time, and nondestructive detection of the freshness of chilled broiler poultry. The principle of color development is that an increase in the volatile sulfide content leads to a change in the absorption wavelength caused by the etching of the Ag-Fe NTs, resulting in a color change (yellow to brown). The minimum H₂S concentrations detected by the naked eye and UV-vis spectrophotometer were 4 and 2 mg/m³, respectively. This label is economical and practical and can monitor the spoilage of chilled broiler meat products in real-time.

Pt-Based Oxygen Reduction Reaction Catalysts in Proton Exchange Membrane Fuel Cells: Controllable Preparation and Structural Design of Catalytic Layer

Proton exchange membrane fuel cells (PEMFCs) have attracted extensive attention because of their high efficiency, environmental friendliness, and lack of noise pollution. However, PEMFCs still face many difficulties in practical application, such as insufficient power density, high cost, and poor durability. The main reason for these difficulties is the slow oxygen reduction reaction (ORR) on the cathode due to the insufficient stability and catalytic activity of the catalyst. Therefore, it is very important to develop advanced platinum (Pt)-based catalysts to realize low Pt loads and long-term operation of membrane electrode assembly (MEA) modules to improve the performance of PEMFC. At present, the research on PEMFC has mainly been focused on two areas: Pt-based catalysts and the structural design of catalytic layers. This review focused on the latest research progress of the controllable preparation of Pt-based ORR catalysts and structural design of catalytic layers in PEMFC. Firstly, the design principle of advanced Pt-based catalysts was introduced. Secondly, the controllable preparation of catalyst structure, morphology, composition and support, and their influence on catalytic activity of ORR and overall performance of PEMFC, were discussed. Thirdly, the effects of optimizing the structure of the catalytic layer (CL) on the performance of MEA were analyzed. Finally, the challenges and prospects of Pt-based catalysts and catalytic layer design were discussed.

Strained Pt(221) Facet in a PtCo@Pt-Rich Catalyst Boosts Oxygen Reduction and Hydrogen Evolution Activity

Over the last years, the development of highly active and durable Pt-based electrocatalysts has been identified as the main target for a large-scale industrial application of fuel cells. In this work, we make a significant step ahead in this direction by preparing a high-performance electrocatalyst and suggesting new structure-activity design concepts which could shape the future of oxygen reduction reaction (ORR) catalyst design. For this, we present a new one-dimensional nanowire catalyst consisting of a L1₀ ordered intermetallic PtCo alloy core and compressively strained high-index facets in the Pt-rich shell. We find the nanoscale PtCo catalyst to provide an excellent turnover for the ORR and hydrogen evolution reaction (HER), which we explain from high-resolution transmission electron microscopy and density functional theory calculations to be due to the high ratio of Pt(221) facets. These facets include highly active ORR and HER sites surprisingly on the terraces which are activated by a combination of sub-surface Co-induced high Miller index-related strain and oxygen coverage on the step sites. The low dimensionality of the catalyst provides a cost-efficient use of Pt. In addition, the high catalytic activity and durability are found during both half-cell and proton exchange membrane fuel cell (PEMFC) operations for both ORR and HER. We believe the revealed design concepts for generating active sites on the Pt-based catalyst can open up a new pathway toward the development of high-performance cathode catalysts for PEMFCs and other catalytic systems.

Heterometallic nanomaterials: activity modulation, sensing, imaging and therapy

Heterometallic nanomaterials (HMNMs) display superior physicochemical properties and stability to monometallic counterparts, accompanied by wider applications in the fields of catalysis, sensing, imaging, and therapy due to synergistic effects between multi-metals in HMNMs. So far, most reviews have mainly concentrated on introduction of their preparation approaches, morphology control and applications in catalysis, assay of heavy metal ions, and antimicrobial activity. Therefore, it is very important to summarize the latest investigations of activity modulation of HMNMs and their recent applications in sensing, imaging and therapy. Taking the above into consideration, we briefly underline appealing chemical/physical properties of HMNMs chiefly tailored through the sizes, shapes, compositions, structures and surface modification. Then, we particularly emphasize their widespread applications in sensing of targets (e.g. metal ions, small molecules, proteins, nucleic acids, and cancer cells), imaging (frequently involving photoluminescence, fluorescence, Raman, electrochemiluminescence, magnetic resonance, X-ray computed tomography, photoacoustic imaging, etc.), and therapy (e.g. radiotherapy, chemotherapy, photothermal therapy, photodynamic therapy, and chemodynamic therapy). Finally, we present an outlook on their forthcoming directions. This timely review would be of great significance for attracting researchers from different disciplines in developing novel HMNMs.

Electrolysis on a Chip with Tunable Thin Film Nanostructured PGM Electrocatalysts Generated from Self-Assembled Block Copolymer Templates

Self-assembled block copolymers are promising templates for fabricating thin film materials with tuned periodic feature sizes and geometry at the nanoscale. Here, a series of nanostructured platinum and iridium oxide electrocatalysts templated from poly(styrene)-block-poly(vinyl pyridine) (PSbPVP) block copolymers via an incipient wetness impregnation (IWI) pathway is reported. Both nanowire and nanocylinder electrocatalysts of varying feature sizes are assessed and higher catalyst loadings are achieved by the alkylation of the pyridine moieties in the PVP block prior to IWI. Electrocatalyst evaluations featuring hydrogen pump and water electrolysis demonstrations are carried out on interdigitated electrode (IDE) chips flexible with liquid supporting electrolytes and thin film polymer electrolytes. Notably, the mass activities of the nanostructured electrocatalysts from alkylated block copolymer templates are 35%-94% higher than electrocatalysts from non-alkylated block copolymer templates. Standing cylinder nanostructures lead to higher mass activities than lamellar variants despite their not having the largest surface area per unit catalyst loading demonstrating that mesostructure architectures have a profound impact on reactivity. Overall, IDE chips with model thin film electrocatalysts prepared from self-assembled block copolymers offer a high-throughput experimental method for correlating electrocatalyst nanostructure and composition to electrochemical reactivity.

Au@Pt Core-Shell Nanoparticle Bioconjugates for the Therapy of HER2+ Breast Cancer and Hepatocellular Carcinoma. Model Studies on the Applicability of 193mPt and 195mPt Radionuclides in Auger Electron Therapy

^193mPt and ^195mPt radionuclides are therapeutically attractive Auger electron emitters with notably high Auger electron yield per decay. The present paper summarizes the first step of research on the applications of core-shell (Au@Pt) nanoparticles for electron Auger therapy of HER2+ (human epidermal growth factor receptor 2) breast cancer and hepatocellular carcinoma. Gold nanoparticles (30 nm) were synthesized covered with a platinum shell at high efficiency (>80%) and were further evaluated for in vitro studies such as binding affinity, internalization and cytotoxicity. To find the mechanism(s) responsible for platinum cytotoxicity in HepG2 cells, the platinum concentration in isolated cell nuclei and cytoplasm was determined using ICP-MS (inductively coupled plasma mass spectrometry). Lack of platinum in cell nuclei suggests that the cytotoxic effect is associated with the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS). Studies carried out on the SKOV-3 cell line with the use of a synthesized targeting bioconjugate (Au@Pt-PEG-trastuzumab) revealed a high affinity of this preparation to HER2+ cells, its internalization, its placement in the perinuclear area and partial intranuclear location. The specific binding for HER2 negative cells, MDA-MB-231, was negligible and Au@Pt-PEG-trastuzumab did not enter these cells. The results obtained are promising and warrant future investigation of Auger electron therapy using ^193mPt and ^195mPt based radiopharmaceuticals.

Twin-Directed Deposition of Pt on Pd Icosahedral Nanocrystals for Catalysts with Enhanced Activity and Durability toward Oxygen Reduction

Platinum nanocrystals featuring a multiply twinned structure and uniform sizes below 5 nm are superb catalytic materials, but it is difficult to synthesize such particles owing to the high twin-boundary energy (166 mJ/m²) of Pt. Here, we report a simple route to the synthesis of such nanocrystals by selectively growing them from the vertices of Pd icosahedral seeds. The success of this synthesis critically depends on the introduction of Br^- ions to slow the reduction kinetics of the Pt(II) precursor while limiting the surface diffusion of Pt adatoms by conducting the synthesis at 30 °C. Owing to the small size and multiply twinned structure of Pt dots, the as-obtained Pd-Pt nanocrystals show remarkably enhanced activity and durability toward oxygen reduction, with a mass activity of 1.23 A mg^-1_Pt and a specific activity of 0.99 mA cm^-2_Pt, which are 8.2 and 4.5 times as high as those of the commercial Pt/C.

Ru single atoms and nanoparticles on carbon nanotubes as multifunctional catalysts

In the last decade we have witnessed increasing interest in the production of renewable energy and value-added chemicals through sustainable and low-cost technologies where catalysts play a crucial role. Herein, we report the application of a Ru/CNT material containing a mixture of Ru single atoms and Ru nanoparticles as a multifunctional catalyst for both the catalytic reduction of nitroarenes and the electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The catalytic activity of the Ru-CNT material was evaluated in the reduction of 4-nitrophenol (4-NP), 4-nitroaniline (4-NA) and 2-nitrophenol (2-NP) in the presence of sodium borohydride as a reducing agent at room temperature, showing high catalytic activity with normalized rate constants (k_nor) of 19.0 × 10³, 57.7 × 10³ and 16.6 × 10³ min^-1 mmol^-1 respectively. Furthermore, the catalyst could be reused in at least 10 cycles without catalytic activity loss, confirming the high stability and robustness of the material. The Ru/CNT material also showed good ORR electrocatalytic activity in alkaline medium with E_onset of 0.76 V vs. RHE, a diffusion-limited current density of 3.89 mA cm^-2 and ñ_O2 of 3.3. In addition, Ru/CNT was remarkably insensitive to methanol with a current retention of 93% (51% for Pt/C) and competitive electrochemical stability of 80% after 20 000 s. Moreover, Ru/CNT was active for the OER with j_max = 29.5 mA cm^-2 at E = 1.86 V vs. RHE, η₁₀ = 0.50 V and good stability (η₁₀ changed to 0.01 V and j_max only decreased by ≈12% after 500 cycles).

Ultrasound-assisted transformation from waste biomass to efficient carbon-based metal-free pH-universal oxygen reduction reaction electrocatalysts

Efficient carbon-based nitrogen-doped electrocatalysts derived from waste biomass are regarded as a promising alternative to noble metal catalysts for oxygen reduction reaction (ORR), which is crucial to fuel cell performance. Here, coconut palm leaves are employed as the carbon source and a series of nitrogen-doped porous carbons were prepared by virtue of a facile and mild ultrasound-assisted method. The obtained carbon material (ANDC-900-10) conveys excellent pH-universal catalytic activity with onset potentials (E_onset) of 1.01, 0.91 and 0.84 V vs. RHE, half-wave potentials (E_1/2) of 0.87, 0.74 and 0.66 V vs. RHE and limiting current densities (J_L) of 5.50, 5.45 and 4.97 mA cm^-2 in alkaline, neutral and acidic electrolytes, respectively, prevailing over the commercial Pt/C catalyst and, what's more, ANDC-900-10 displays preeminent methanol crossover resistance and long-term stability in the broad pH range (0-13), thanks to its abundant hierarchical nanopores as well as effective nitrogen doping with high-density pyridinic-N and graphitic-N. This work provides sonochemical insight for underpinning the eco-friendly approach to rationally designing versatile metal-free carbon-based catalysts toward the ORR at various pH levels.

Elucidation of Active Sites on S, N Codoped Carbon Cubes Embedding Co-Fe Carbides toward Reversible Oxygen Conversion in High-Performance Zinc-Air Batteries

The development of high-performance but low-cost catalysts for the electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of central importance for realizing the prevailing application of metal-air batteries. Herein a facile route is devised to synthesize S, N codoped carbon cubes embedding Co-Fe carbides by pyrolyzing the Co-Fe Prussian blue analogues (PBA) coated with methionine. Via the strong metal-sulfur interaction, the methionine coating provides a robust sheath to restrain the cubic morphology of PBA upon pyrolysis, which is proved highly beneficial for promoting the specific surface area and active sites exposure, leading to remarkable bifunctionality of ORR and OER comparable to the benchmarks of Pt/C and RuO₂ . Further elaborative investigations on the activity origin and postelectrolytic composition unravel that for ORR the high activity is mainly contributed by the S, N codoped carbon shell with the inactive carbide phase converting into carbonate hydroxides. For OER, the embedded Co-Fe carbides transform in situ into layered (hydr)oxides, serving as the actual active sites for promoting water oxidation. Zn-air batteries employing the developed hollow structure as the air cathode catalyst demonstrate superb rechargeability, energy efficiency, as well as portability.

Platinum nanoparticles stabilized by N-heterocyclic thiones. Synthesis and catalytic activity in mono- and di-hydroboration of alkynes

N-Heterocyclic Thiones (NHT) proved to be efficient ligands for the stabilization of small platinum nanoparticles (1.3-1.7 nm), synthesized by decomposition of [Pt(dba)₂], under a H₂ atmosphere, in the presence of variable sub-stoichiometric amounts of the NHT. Full characterization by means of TEM, HR-TEM, NMR, ICP, TGA and XPS have been carried out, providing information about the nature of the metal nanoparticles and the interaction of the NHT ligands to the metal surface. Importantly, DFT calculations indicate that some NHT ligands interact with the metal through the C[double bond, length as m-dash]C double bond of the imidazole fragment in addition to the sulfur atom, thus providing additional stabilization to the nanoparticles. According to XPS, TGA and ICP techniques, the surface coverage by the ligand increases by decreasing the size of the substituents on the nitrogen atom. The platinum nanoparticles have been used as catalyst in the hydroboration of alkynes. The most active system is that with a less covered surface area lacking an interaction of the ligand by means of the C[double bond, length as m-dash]C double bond. This catalyst hydroborates alkynes with excellent selectivities towards the monoborylated anti-Markovnikov product (vinyl-boronate) when one equiv. of borane is used. Very interestingly, aliphatic alkynes undergo a second hydroborylation process leading to the corresponding 1,1- and 1,2-diboroylated species with good selectivities towards the former.

Oxygen Reduction Activities of Strained Platinum Core-Shell Electrocatalysts Predicted by Machine Learning

Core-shell nanocatalyst activities are chiefly controlled by bimetallic material composition, shell thickness, and nanoparticle size. We present a machine learning framework predicting strain with site-specific precision to rationalize how strain on Pt core-shell nanocatalysts can enhance oxygen reduction activities. Large compressive strain on Pt@Cu and Pt@Ni induces optimal mass activities at 1.9 nm nanoparticle size. It is predicted that bimetallic Pt@Au and Pt@Ag have the best mass activities at 2.8 nm, where active sites are exposed to weak compressive strain. We demonstrate that optimal strain depends on the nanoparticle size; for instance, strengthening compressive strain on 1.92 nm sized Pt@Cu and Pt@Ni, or weakening compressive strain on 2.83 nm sized Pt@Ag and Pt@Au, can lead to further enhanced mass activities.

Core-shell structured PtRu nanoparticles@FeP promoter with an efficient nanointerface for alcohol fuel electrooxidation

In this study, a bottleneck was overcome for direct alcohol fuel cells using state-of-the-art PtRu catalysts for alcohol fuel oxidation. Herein, a core-shell structured PtRu catalyst system based on the emerging promoter FeP was developed that showed excellent catalytic performance for the oxidation of alcohol fuels. The surface spectrometric analysis and morphology observation confirmed the formation of a nanointerface of the PtRu shell and FeP core hybrid catalyst (PtRu@FeP), and efficient ligand effects and electronic effects were found to result from the noble metal active sites and adjacent promoter in the core-shell structure. The facile formation of oxygen-containing species and the strong electronic effects could activate the Pt active sites, leading to high catalytic performance. High anti-CO poisoning ability was found for this catalyst system when compared with the case of the benchmark commercial PtRu/C catalyst (110 mV less and 60 mV less as evaluated by the peak and onset potentials for CO oxidation, respectively). The PtRu@FeP catalysts also exhibited much higher catalytic activity and stability when compared with commercial and home-made PtRu/C catalysts; specifically, the peak current density of the PtRu@FeP 1 : 1 catalyst was about 2 and 3 times higher than those of the commercial PtRu/C catalyst and home-made PtRu/C for the oxidation of the alcohol fuels methanol and ethanol; moreover, high catalytic efficiency, improved by 2 times, was found, as expressed by the specific activity. Excellent catalytic stability as evaluated by 1000 cycles of cyclic voltammetry measurements was also demonstrated for the PtRu@FeP catalysts. The high catalytic performance could be attributed to the intimate nanointerface contact of the core-shell structured PtRu shell over the FeP core via a bi-functional catalytic mechanism and electronic effects based on the ligand effect in this catalyst system. The current study is a significant step to increase the PtRu catalytic performance via nanointerface construction by a core-shell structure on a novel promoter for direct alcohol fuel cells.

Size, Composition, and Support-Doping Effects on Oxygen Reduction Activity of Platinum-Alloy and on Non-platinum Metal-Decorated-Graphene Nanocatalysts

Recent investigations reported in the open literature concerning the functionalization of graphene as a support material for transition metal nanoparticle catalysts have examined isolated systems for their potential Oxygen Reduction Reaction (ORR) activity. In this work we present results which characterize the ability to use functionalized graphene (via dopants B, N) to upshift and downshift the adsorption energy of mono-atomic oxygen, O* (the ORR activity descriptor on ORR Volcano Plots), for various compositions of 4-atom, 7-atom, and 19-atom sub-nanometer binary alloy/intermetallic transition metal nanoparticle catalysts on graphene (TMNP-MDG). Our results show several important and interesting features: (1) that the combination of geometric and electronic effects makes development of simple linear mixing rules for size/composition difficult; (2) that the transition from 4- to 7- to 19-atom TMNP on MDG has pronounced effects on ORR activity for all compositions; (3) that the use of B and N as dopants to modulate the graphene-TMNP electronic structure interaction can cause shifts in the oxygen adsorption energy of 0.5 eV or more; (4) that it might be possible to make specific doped-graphene-Ni_xCu_y TMNP systems which fall close to the Volcano Peak for ORR. Our results point to systems which should be investigated experimentally and may improve the viability of future fuel cell or other ORR applications, and provide new paths for future investigations of more detail for TMNP-MDG screening.

Generalized Synthetic Strategy for Transition-Metal-Doped Brookite-Phase TiO2 Nanorods

We report a generalized wet-chemical methodology for the synthesis of transition-metal (M)-doped brookite-phase TiO₂ nanorods (NRs) with unprecedented wide-range tunability in dopant composition (M = V, Cr, Mn, Fe, Co, Ni, Cu, Mo, etc.). These quadrangular NRs can selectively expose {210} surface facets, which is induced by their strong affinity for oleylamine stabilizer. This structure is well preserved with variable dopant compositions and concentrations, leading to a diverse library of TiO₂ NRs wherein the dopants in single-atom form are homogeneously distributed in a brookite-phase solid lattice. This synthetic method allows tuning of dopant-dependent properties of TiO₂ nanomaterials for new opportunities in catalysis applications.

Amplified oxygen reduction signal at a Pt-Sn-modified TiO2 nanocomposite on an electrochemical aptasensor

In this work, a metallic composite with strong electrocatalytic property was designed by uniformly decorating Pt and Sn nanoparticles on the surface of TiO₂ nanorods (Pt-Sn@TiO₂). A detection scheme was then developed based on a dual signal amplification strategy involving the Pt-Sn@TiO₂ composite and exonuclease assisted target recycling. The Pt-Sn@TiO₂ composite exhibited an enhanced oxygen reduction current owing to the synergistic effect between Pt and Sn, as well as high exposure of Pt (111) crystal face. Initially, a Pt-Sn@TiO₂ modified glassy carbon electrode produced an amplified electrochemical signal for the reduction of dissolved oxygen in the analyte solution. Next, a DNA with a complementary sequence to a streptomycin aptamer (cDNA) was immobilised on the Pt-Sn@TiO₂ modified electrode, followed by the streptomycin aptamer that hybridised with cDNA. The corresponding oxygen reduction current was diminished by 51% attributable to the hindrance from the biomolecules. After a mixture of streptomycin and RecJ_f exonuclease was introduced, both the streptomycin-aptamer complex and the cDNA were cleaved from the electrode, making the Pt-Sn and Pt (111) surface available for oxygen reduction. RecJ_f would also release streptomycin from the streptomycin-aptamer complex, allowing it to complex again with aptamers on the electrode. This has then promoted a cyclic amplification of the oxygen reduction current by 85%, which is quantitatively related to streptomycin. Under optimal conditions, the aptasensor exhibited a linear range of 0.05-1500 nM and a limit of detection of 0.02±0.0045 nM streptomycin. The sensor was then used in the real-life sample detection of streptomycin to demonstrate its potential applications to bioanalysis.

A Cathode-Integrated Sulfur-Deficient Co9S8 Catalytic Interlayer for the Reutilization of "Lost" Polysulfides in Lithium-Sulfur Batteries

Lithium-sulfur batteries, with their high theoretical energy density and the low material cost of sulfur, are highly promising as a post-lithium ion battery contender. Their current performance is however compromised by sulfur loss and polysulfide shuttle to result in low energy efficiency and poor cycle stability. Herein, a catalytic material (Co₉S_{8- x}/CNT, nanoparticles with a metallic Co₉S₈ core and a sulfur-deficient shell on a CNT support) was applied as an interlayer on the sulfur cathode to retain migratory polysulfides and promote their reutilization. The Co₉S_{8- x}/CNT catalyst is highly effective for the conversion of polysulfides to insoluble end products (S or Li₂S/Li₂S₂), and its deployment as a cathode-integrated interlayer was able to retain the polysulfides in the cathode for reuse. The accumulation of polysulfides in the electrolyte and the polysulfide shuttle were significantly reduced as a result. Consequently, a host-free sulfur cathode with the Co₉S_{8- x}/CNT interlayer had a low capacity fade rate of 0.049% per cycle for 1000 cycles at a 0.3C rate, a significant improvement of the capacity fade rate without it (0.28% per cycle for 200 cycles). The results here provide not only direct evidence for the contributions of sulfur deficiencies on the catalytic activity of Co₉S₈ in polysulfide conversion reactions but also the methodology on how the catalyst should be deployed in a Li-S battery for the best catalytic outcome.

Peptide-Assisted 2-D Assembly toward Free-Floating Ultrathin Platinum Nanoplates as Effective Electrocatalysts

We demonstrate the 2-D anisotropic formation of ultrathin free-floating Pt nanoplates from the assembly of small nanocrystals using T7 peptide (Ac-TLTTLTN-CONH₂). As-formed nanoplates are rich in grain boundaries that can promote their catalytic activities. Furthermore, we demonstrate that a minor number of Pd atoms can selectively deposit on and stabilize the grain boundaries, which leads to enhanced structure stability. The Pd-enhanced Pt polycrystal nanoplates show great oxygen reduction reaction activities with 15.5 times higher specific activity and 13.7 times higher mass activity than current state-of-the-art commercial Pt/C electrocatalysts as well as 2.5 times higher mass activity for hydrogen evolution reaction compared with Pt/C.

Electrochemical Conversion of Biomass-Based Oxygenated Compounds

Dwindling fossil fuel resources and substantial release of CO2 from their processing have increased the appeal to use biomass as a sustainable platform for synthesis of chemicals and fuels. Steps toward this will require selective upgrading of biomass to suitable intermediates. Traditionally, biomass upgrading has involved thermochemical processes that require excessive amounts of petrochemical-derived H2 and suffer from poor product selectivity. Electrochemical routes have emerged as promising alternatives because of ( a) the replacement of petrochemical-derived H2 by protons generated in situ, ( b) mild operating temperatures and pressures, and ( c) the use of electrode potential to tune reaction rates and product selectivity. In this review, we highlight the advances in the electrocatalytic hydrogenation and oxidation of biomass-derived platform molecules. The effects of important reaction parameters on electrochemical efficiency and catalytic activity/selectivity are thoroughly discussed. We conclude by summarizing current challenges and discussing future research directions.

Tuning the oxygen evolution reaction on a nickel-iron alloy via active straining

We report that one can gain active control of the electrocatalytic oxygen evolution reaction (OER) on Ni3Fe thin films via externally applied strains. The combination of theory and experiments shows that an elastic strain on the surface can tune the OER activity in a predictable way that is consistent with the d-band model. The OER overpotential can be lowered by uniaxial tensions and increased by compressions in a linear manner.

High-level nitrogen-doped, micro/mesoporous carbon as an efficient metal-free electrocatalyst for the oxygen reduction reaction: optimizing the reaction surface area by a solvent-free mechanochemical method

Acting as an efficient metal-free ORR electrocatalyst, nitrogen-doped porous carbon derived from coconut mesocarp was prepared by a solvent-free ball-milling process.