Cyclic Penta-Twinned Rhodium Nanobranches as Superior Catalysts for Ethanol Electro-oxidation

D-Band Engineering in Pd-Based Nanowire Networks for Further Enhancement in Ethanol Electrooxidation Reaction

The development of highly efficient electrocatalysts for the ethanol oxidation reaction (EOR) is essential for the commercialization of direct ethanol fuel cells, yet challenges remain. In this study, a one-pot solution-phase method to synthesize Pd nanowire networks (NNWs) with very high surface-to-volume ratio having numerous twin and grain boundaries is developed. Using the same method, the Pd lattice is further engineered by introducing Ag and Cu atoms to produce AgPd, and CuPd alloy structure which significantly shifts the Pd d-band center upward and downward, respectively due to strain and ligand effects. Theoretical analysis employing density functional theory (DFT) demonstrates that such modification of the d-band center significantly influences the adsorption energies of reactants on the catalytic surface. Owing to their notably high surface-to-volume ratio and the presence of multiple twin and grain boundaries, Pd NNWs demonstrate significantly enhanced electrocatalytic activity toward EOR, ≈7.2 times greater than that of commercial Pd/C. Remarkably, compared to Pd NNWs, AgPd, and CuPd NNWs display enlarged and reduced electrocatalytic activity toward EOR, respectively. Specifically, Ag4Pd7 NNWs achieve a remarkable mass activity of 9.00 A mgpd -1 for EOR, which is 13.6 times higher than commercial Pd/C.

Recent Approaches for Cleaving the C─C Bond During Ethanol Electro-Oxidation Reaction

Direct ethanol fuel cells (DEFCs) play an indispensable role in the cyclic utilization of carbon resources due to its high volumetric energy density, high efficiency, and environmental benign character. However, owing to the chemically stable carbon-carbon (C─C) bond of ethanol, its incomplete electrooxidation at the anode severely inhibits the energy and power density output of DEFCs. The efficiency of C─C bond cleaving on the state-of-the-art Pt or Pd catalysts is reported as low as 7.5%. Recently, tremendous efforts are devoted to this field, and some effective strategies are put forward to facilitate the cleavage of the C─C bond. It is the right time to summarize the major breakthroughs in ethanol electrooxidation reaction. In this review, some optimization strategies including constructing core-shell nanostructure with alloying effect, doping other metal atoms in Pt and Pd catalysts, engineering composite catalyst with interface synergism, introducing cascade catalytic sites, and so on, are systematically summarized. In addition, the catalytic mechanism as well as the correlations between the catalyst structure and catalytic efficiency are further discussed. Finally, the prevailing limitations and feasible improvement directions for ethanol electrooxidation are proposed.

A universal synthesis strategy of Pd-based trimetallic nanowires for efficient alcohol electrooxidation

Trimetallic nanowires (NWs) have drawn much attention in efficient alcohol oxidation reaction (AOR) due to their unique features, including high atomic utilization efficiency and fast electron transfer ability. However, a universal strategy to synthesize Pd-based trimetallic NWs with high catalytic performance is still lacking. Herein, we develop a universal method for facile synthesis of PdBiM (M = Pt, Ru, Ir, Co, Cu) NWs with excellent AOR activities. By taking PdBiPt NWs as an example, the formation mechanism was investigated, and it is found that introduction of bismuth (Bi) plays an important role in facilitating the formation of the NW structure. Moreover, the PdBiPt NWs deliver an outstanding performance toward both the ethanol oxidation reaction (EOR) and the methanol oxidation reaction (MOR). Density functional theory (DFT) calculations together with experimental results disclose that the moderate electronic structure of trimetallic PdBiPt NWs can optimize the adsorption of OHads and weaken the adsorption of COads, thereby leading to the substantially enhanced AOR performance. We believe that this work can inspire the design of multimetallic NWs as high-performance catalysts.

Self-Interface in Rh Nanosheets-Supported Tetrahedral Rh Nanocrystals for Promoting Electrocatalytic Oxidation of Ethanol

Direct ethanol fuel cells hold great promise as a power source. However, their commercialization is limited by anode catalysts with insufficient selectivity toward a complete oxidation of ethanol for a high energy density, as well as sluggish catalytic kinetics and low stability. To optimize the catalytic performance, rationally tuning surface structure or interface structure is highly desired. Herein, a facile route is reported to the synthesis of Rh nanosheets-supported tetrahedral Rh nanocrystals (Rh THs/NSs), which possess self-supporting homogeneous interface between Rh tetrahedrons and Rh nanosheets. Due to full leverage of the structural advantages within the given structure and construction of interfaces, the Rh THs/NSs can serve as highly active electro-catalysts with excellent mass activity and selectivity toward ethanol electro-oxidation. The in situ Fourier transform infrared reflection spectroscopy showed the Rh THs/NSs exhibit the highest C1 pathway selectivity of 23.2%, far exceeding that of Rh nanotetrahedra and Rh nanosheets. Density function theory calculations further demonstrated that self-interface between Rh nanosheets and tetrahedra is beneficial for C-C bond cleavage of ethanol. Meanwhile, the self-supporting of 2D nanosheets greatly enhance the stability of tetrahedra, which improves the catalytic stability.

Interfacial Electron Engineering of PdSn-NbN/C for Highly Efficient Cleavage of the C-C Bonds in Alkaline Ethanol Electrooxidation

The splitting of the C-C bonds of ethanol remains a key issue to be addressed, despite tremendous efforts made over the past several decades. This study highlights the enhancement mechanism of inexpensive NbN-modified Pd1 Sn3 -NbN/C towards the C-C bonds cleavage for alkaline ethanol oxidation reaction (EOR). The optimal Pd1 Sn3 -NbN/C delivers a catalytic activity up to 43.5 times higher than that of commercial Pd/C and high carbonate selectivity (20.5%) toward alkaline EOR. Most impressively, the Pd1 Sn3 -NbN/C presents good durability even after 25 200 s of chronoamperometric testing. The enhanced catalytic performance is mainly due to the interfacial interaction between PdSn and NbN, demonstrated by multiple structural characterization results. In addition, in situ ATR-SEIRAS (Attenuated total reflection-surface enhanced infrared absorption spectroscopy) results suggest that NbN facilitates the C-C bonds cleavage towards the alkaline EOR, followed by the enhanced OH adsorption to promote the subsequent oxidation of C1 intermediates after doping Sn. DFT (density functional theory) calculations indicate that the activation barriers of the C-H bond cleavage in CH3 CH2 OH, CH3 CHOH, CH3 CHO, CH3 CO, CH2 CO, and the C-C bond cleavage in CH3 CO, CH2 CO, CHCO are evidently reduced and the removal of adsorbed CH3 CO and CO becomes easier on the PdSn-NbN/C catalyst surface.

Assembly of Alloyed PdM (Ag, Cu, and Sn) Nanosheets and Their Electrocatalytic Oxidation of Ethanol and Methanol

Direct alcohol fuel cells are popular due to their high energy density, abundant sources, and ease of transportation and storage. Palladium-based nanosheet self-assembled materials have emerged as an effective catalyst for alcohol oxidation reactions. In this work, nanosheets were synthesized with the same feeding ratio assembly of alloyed PdM (M = Ag, Cu, and Sn). The introduction of the second element was able to enhance the catalytic response of the catalysts to alcohol electrooxidation. Among them, the PdCu alloy exhibited the best performance in terms of catalytic activity, toxicity resistance, and stability to ethanol oxidation reaction (EOR) and methanol oxidation reaction (MOR). The catalytic current densities for EOR can reach 2226, 2518, and 1598 mA mg-1 for PdAg, PdCu, and PdSn nanosheet assemblies, respectively. These are mainly attributed to better electronic effects, altered atomic distances within the cell for the d-band centers of Pd, and a larger electrochemical active surface area (ECSA). The optimized d-band center is beneficial to promote the catalytic performance of EOR and MOR. Experimental data also demonstrated that higher electrocatalytic temperature, higher pH, and higher alcohol concentration can accelerate the rate of alcohol electrooxidation. These results have the potential to be extended to Pd-M (M = other metals) nanosheets and help for a wider range of catalytic applications.

Bimetallic Pt-Hg Aerogels for Electrocatalytic Upgrading of Ethanol to Acetate

Electrochemical upgrading of ethanol to acetic acid provides a promising strategy to couple with the current hydrogen production from water electrolysis. This work reports the design of a series of bimetallic PtHg aerogels, where the PtHg aerogel exhibits a 10.5-times higher mass activity than that of commercial Pt/C toward ethanol oxidation. More impressively, the PtHg aerogel demonstrates nearly 100% selectivity toward the production of acetic acid. The operando infrared spectroscopic studies and nuclear magnetic resonance analysis verify the preferable C2 pathway mechanism during the reaction. This work opens an avenue for the electrochemical synthesis of acetic acid via ethanol electrolysis.

Noble metal nanodendrites: growth mechanisms, synthesis strategies and applications

Inorganic nanodendrites (NDs) have become a kind of advanced nanomaterials with broad application prospects because of their unique branched architecture. The structural characteristics of nanodendrites include highly branched morphology, abundant tips/edges and high-index crystal planes, and a high atomic utilization rate, which give them great potential for usage in the fields of electrocatalysis, sensing, and therapeutics. Therefore, the rational design and controlled synthesis of inorganic (especially noble metals) nanodendrites have attracted widespread attention nowadays. The development of synthesis strategies and characterization methodology provides unprecedented opportunities for the preparation of abundant nanodendrites with interesting crystallographic structures, morphologies, and application performances. In this review, we systematically summarize the formation mechanisms of noble metal nanodendrites reported in recent years, with a special focus on surfactant-mediated mechanisms. Some typical examples obtained by innovative synthetic methods are then highlighted and recent advances in the application of noble metal nanodendrites are carefully discussed. Finally, we conclude and present the prospects for the future development of nanodendrites. This review helps to deeply understand the synthesis and application of noble metal nanodendrites and may provide some inspiration to develop novel functional nanomaterials (especially electrocatalysts) with enhanced performance.

The Role of Bismuth in Suppressing the CO Poisoning in Alkaline Methanol Electrooxidation: Switching the Reaction from the CO to Formate Pathway

While tuning the electronic structure of Pt can thermodynamically alleviate CO poisoning in direct methanol fuel cells, the impact of interactions between intermediates on the reaction pathway is seldom studied. Herein, we contrive a PtBi model catalyst and realize a complete inhibition of the CO pathway and concurrent enhancement of the formate pathway in the alkaline methanol electrooxidation. The key role of Bi is enriching OH adsorbates (OH_ad) on the catalyst surface. The competitive adsorption of CO adsorbates (CO_ad) and OH_ad at Pt sites, complementing the thermodynamic contribution from alloying Bi with Pt, switches the intermediate from CO_ad to formate that circumvents CO poisoning. Hence, 8% Bi brings an approximately 6-fold increase in activity compared to pure Pt nanoparticles. This notion can be generalized to modify commercially available Pt/C catalysts by a microwave-assisted method, offering opportunities for the design and practical production of CO-tolerance electrocatalysts in an industrial setting.

Microwave-assisted synthesis of octahedral Rh nanocrystals and their performance for electrocatalytic oxidation of formic acid

Uniform and well-defined octahedral Rh nanocrystals were rapidly synthesized in a domestic microwave oven for only 140 s of irradiation by reducing Rh(acac)₃ with tetraethylene glycol (TEG) as both a solvent and a reducing agent in the presence of an appropriate amount of KI, didecyl dimethyl ammonium chloride (DDAC), ethylene diamine (EDA) and polyvinylpyrrolidone (PVP). KI, DDAC and EDA were essential for the creation of octahedral Rh nanocrystals. Electrochemical measurements showed a significantly enhanced electrocatalytic activity and stability for the as-prepared octahedral Rh nanocrystals compared with commercial Rh black.

Coating Porous TiO2 Films on Carbon Nanotubes to Enhance the Durability of Ultrafine PtCo/CNT Nanocatalysts for the Oxygen Reduction Reaction

The development of excellent activity and durability catalysts for the oxygen reduction reaction (ORR) is essential for the commercialization of proton exchange membrane fuel cells (PEMFCs). Reducing the size of catalyst particles can provide more reaction sites to mitigate the performance degradation caused by reduced platinum loading. However, at the same time, it makes the particles more prone to agglomeration and exfoliation, leading to a rapid reduction in catalyst activity. Here, we present the design of a composite support (TiO₂/CNT) with a porous TiO₂ film that immobilizes PtCo nanoparticles (NPs) loaded on the support while protecting the carbon nanotubes inside. The particle size of PtCo NPs was only 1.99 nm (determined by transmission electron microscopy), but the nanocatalyst (PtCo/TiO₂/CNT) maintained high catalytic performance and stability on account of the strong metal support interaction (SMSI). PtCo/TiO₂/CNT exhibited a high mass activity (MA, 0.476 A mg_Pt^-1) and was found to have MA retention rates of 91.7 and 88.8% in durability tests performed at 0.6-1.0 V and 1.0-1.5 V, respectively.

CO2 and Formate Pathway of Methanol Electrooxidation at Rhodium Electrodes in Alkaline Media: An In Situ Electrochemical Attenuated Total Refection Surface-Enhanced Infrared Absorption Spectroscopy and Infrared Reflection Absorption Spectroscopy Investigation

Rh catalysts exhibit unexpected high activity for the methanol oxidation reaction (MOR) in alkaline conditions, making them potential anodic catalysts for direct methanol fuel cells (DMFCs). Nevertheless, the MOR mechanism on Rh electrodes has not been clarified thus far, which impedes the development of high-efficiency Rh-based MOR catalysts. To investigate it, a combination of in situ electrochemical techniques called attenuated total refection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and infrared reflection absorption spectroscopy (IRAS) is used. Cyclic voltammograms of MOR at Rh electrodes show considerable activity in alkaline media rather than acidic media, although the real-time ATR-SEIRA spectral results demonstrate that methanol can rarely self-decompose on Rh at open-circuit conditions. Meanwhile, in combination of ATR-SEIRAS and IRAS results, CO₂ and formate are thought to be MOR products, suggesting a dual-pathway mechanism ("CO₂ pathway" and "formate pathway"). Specifically, CO_ad species, which are the major intermediates in the CO₂ pathway, can produce at lower potentials and be oxidized into CO₂ at a potential of 0.5-0.75 V. Concurrently, the formate can be produced from 0.5 V and diffuse into the bulk electrolyte to become one of the MOR products, while the further electrochemical conversion of formate to CO₂ is essentially negligible. More directly, the apparent selectivity (r) of the CO₂ pathway is estimated to reach ca. 0.63 at 0.9 V, confirming the potential-dependent selectivity of MOR at Rh surfaces. This study might provide fresh insights into the design and fabrication of effective Rh-based catalysts for MOR.

Ultrathin Pd3 Pt1 Rh0.1 Nanorings with Strong C-C Bond Breaking Ability for the Ethanol Oxidation Reaction

Ethanol as a fuel for direct ethanol fuel cells (DEFCs) has the advantages of being highly energetic, environmentally friendly, and low-cost, while the slow anodic ethanol oxidation reaction (EOR), intermediate poisoning effect, and incomplete oxidation of ethanol became obstacles to the development of DEFCs. Herein, a 2D ternary cyclic Pd₃ Pt₁ Rh_0.1 nanorings (NRs) catalyst with efficient EOR performance is prepared via a facile one-pot solvothermal approach, and systematic studies are carried out to reveal the mechanisms of the enhanced performance and C-C bond selectivity. In particular, the optimized catalyst exhibits impressive mass activity, stability, toxicity resistance, and C-C bond cleavage ability. It's proposed that the considerable performance is attributed to the unique hollow structure, providing abundant active sites. The high toxicity resistance is not only attributed to the electronic modulation of the catalyst material by Rh atoms, but also depends on the excellent water activation properties of Rh, which contribute to the removal of intermediates, such as CO. In addition, the density functional theory calculations showed that the introduction of Rh significantly enhances the C-C bond cleavage ability of the catalyst, further improving the EOR activity.

Boosting Hydrogen Production by Selective Anodic Electrooxidation of Ethanol over Trimetallic PdSbBi Nanoparticles: Composition Matters

The conventional hydrogen evolution from water electrolysis is severely impeded by the sluggish kinetics of oxygen evolution reaction (OER). In this work, an integrated electrolysis system of replacing the anodic OER with a thermodynamically favorable ethanol oxidation reaction (EOR) has been developed by using PdSbBi/C as an electrocatalyst. To maximize the EOR performance, the composition of PdSbBi nanoparticles is tuned by varying the ratio of Sb and Bi precursors. Ternary PdSbBi-based electrocatalysts exhibit enhanced activity and stability toward EOR compared to commercial Pd/C and binary catalysts. In particular, the Pd₇₆Sb₁₇Bi₇/C catalyst delivers a very high specific activity up to 52.4 mA cm^-2 and mass activity of 2.66 A mg^-1_Pd. Besides, this EOR process is demonstrated to have high selectivity with acetic acid as the oxidation product in the electrolyte. When coupled with a cathodic platinum mash, the two-electrode electrolyzer cell requires a voltage input of merely 0.61 V to afford a current density of 10 mA cm^-2. Density functional theory calculations reveal that the presence of Sb and Bi can promote the adsorption of hydroxide ions and facilitate the removal of reaction intermediates in the EOR pathway. This work provides a novel catalyst for the energy-efficient coproduction of acetic acid and hydrogen fuel.

Tailoring Amorphous PdCu Nanostructures for Efficient C-C Cleavage in Ethanol Electrooxidation

The large-scale application of direct ethanol fuel cells has long been obstructed by the sluggish ethanol oxidation reaction at the anode. Current wisdom for designing and fabricating EOR electrocatalysts has been focused on crystalline materials, which result in only limited improvement in catalytic efficiency. Here, we report the amorphous PdCu (a-PdCu) nanomaterials as superior EOR electrocatalysts. The amorphization of PdCu catalysts can significantly facilitate the C-C bond cleavage, which thereby affords a C1 path faradic efficiency as high as 69.6%. Further tailoring the size and shape of a-PdCu nanocatalysts through the delicate kinetic control can result in a maximized mass activity up to 15.25 A/mg_Pd, outperforming most reported catalysts. Notably, accelerated durability tests indicate that both the isotropic structure and one-dimensional shape can dramatically enhance the catalytic durability of the catalysts. This work provides valuable guidance for the rational design and fabrication of amorphous noble metal-based electrocatalysts for fuel cells.

Boron-Intercalation-Induced Phase Evolution of Rh Metallene for Energy-Saving H2 Production by H2 O2 Oxidation Coupled with Water Electrolysis

Tailoring the morphology and crystal structure of metallene is critical to improve its electrocatalytic performance. In this work, hetero-phase RhB metallene (h-RhB metallene) with amorphous/crystalline structure is readily prepared by a two-step method. The h-RhB metallene is very unique in its non-metallic heteroatom doping and amorphous/crystalline structure. Benefiting from the unique metallene structure and the optimized electronic states induced by the incorporation of B atoms, the h-RhB metallene exhibits superior performance for hydrogen evolution reaction and hydrogen peroxide electro-oxidation reaction (HPOR). When coupled with HPOR, the h-RhB metallene||h-RhB metallene water electrolysis two-electrode system exhibits a lower cell voltage of 0.379 V (@ 10 mA cm^-2 ) compared with the overall water splitting (1.35 V). The presented synthetic method provides a powerful strategy to design metallene with hetero-phase for energy-saving H₂ production.

Highly Curved, Quasi-Single-Crystalline Mesoporous Metal Nanoplates Promote CC Bond Cleavage in Ethanol Oxidation Electrocatalysis

The ability to manipulate metal nanocrystals with well-defined morphologies and structures is greatly important in material chemistry, catalysis chemistry, nanoscience, and nanotechnology. Although 2D metals serve as interesting platforms, further manipulating them in solution with highly penetrated mesopores and ideal crystallinity remains a huge challenge. Here, an easy yet powerful synthesis strategy for manipulating the mesoporous structure and crystallinity of 2D metals in a controlled manner with cetyltrimethylammonium chloride as the mesopore-forming surfactant and extra iodine-ion as the structure/facet-selective agent is reported. This strategy allows for preparing an unprecedented type of 2D quasi-single-crystalline mesoporous nanoplates (SMPs) with highly curved morphology and controlled metal composition. The products, for example, PdCu SMPs, feature abundant undercoordinated sites, optimized electronic structures, excellent electron/mass transfers, and confined mesopore environments. Curved PdCu SMPs exhibit remarkable electrocatalytic activity of 6.09 A mg_Pd ^-1 and stability for ethanol oxidation reaction (EOR) compared with its counterpart catalysts and commercial Pd/C. More importantly, PdCu SMPs are highly selective for EOR electrocatalysis that dramatically promotes C-C bond cleavage with a superior C1 pathway selectivity as high as 72.1%.

Unveiling the Synergistic Effects of Monodisperse Sea Urchin-like PdPb Alloy Nanodendrites as Stable Electrocatalysts for Ethylene Glycol and Glycerol Oxidation Reactions

In recent times, the fabrication of noble metal-based catalysts with controllable morphologies has become a research hotspot. Electrocatalytic devices with excellent catalytic performance and enhanced durability for the ethylene glycol oxidation reaction (EGOR) and the glycerol oxidation reaction (GOR) are significant for commercial direct fuel cells. Herein, a series of PdPb sea urchin-like nanodendrite (ND) structures with controllable molar ratios were synthesized as EGOR and GOR electrocatalysts of high efficiency. The optimized structurally regular Pd₃Pb NDs exhibit the best electrocatalytic activity and outstanding stability compared to other samples and commercial Pt/C. In addition, the integrated Pb on Pd₃Pb NDs can mitigate the bond energy the intermediates generate and further boost the electrooxidation of the intermediates by supplying enough active sites without considering its intrinsic structure, which is beneficial to the enhanced EGOR and GOR activity and stability. With the assistance of electrochemical measurement, the mechanism of the enhanced alloy was further investigated. This paper presents a promising strategy to fabricate catalysts with stable structures, which will elucidate a very promising approach for developing Pd-based catalysts for further applications in fuel cells.

Branch-Regulated Palladium-Antimony Nanoparticles Boost Ethanol Electro-oxidation to Acetate

Tuning the composition and morphology of bimetallic nanoparticles (NPs) offers an effective strategy to improve their electrocatalytic performance. In this work, we present a facile wet-chemistry procedure to engineer PdSb NPs with controlled morphology. Spherical or branched NPs are produced by tuning the heterogeneous nucleation of Sb on Pd seeds. Compared with pure Pd NPs, the incorporation of Sb not only decreases the amount of Pd used but also results in a significant increase of activity and stability for the electrocatalytic ethanol oxidation reaction (EOR). Best performances are obtained with highly branched PdSb NPs, which deliver a specific activity of 109 mA cm^-2 and a mass activity of up to 2.42 A mg_Pd^-1, well above that of a commercial Pd/C catalyst and branched Pd NPs. Moreover, PdSb displays significant stability enhancement of over 10 h for the EOR measurements. Density functional theory calculations reveal that the improved performance of PdSb NPs is related to the role played by Sb in reducing the energy barrier of the EOR rate-limiting step. Interestingly, as a side and value-added product of the EOR, acetate is obtained with 100% selectivity on PdSb catalysts.

Assembly of Alloyed PdCu Nanosheets and Their Electrocatalytic Oxidation of Ethanol

Two-dimensional (2D) nanostructured catalysts have attracted great attention in many important fields, including energy applications and chemical industry. In this study, PdCu nanosheet assemblies (NSAs) have been synthesized and investigated as electrocatalysts for direct ethanol fuel cells in an alkaline medium. A great number of active sites on the nanosheets of PdCu NSAs for ethanol electro-oxidation are exposed, where the electron structures are optimized combined with the second element copper. Electrochemical measurements show that PdCu NSA1 exhibits excellent catalytic activity (2536 mA mg^-1) and cyclic stability compared to PdCu NSA2 (1700 mA mg^-1) and PdCu NSA3 (1436 mA mg^-1), much higher than commercial Pd/C. Kinetics studies on the electrolysis of ethanol suggest that PdCu NSAs should be more favorable at higher catalytic temperatures, higher concentrations of ethanol, and low pH value environments. The unique composition and structures PdCu NSA1 would result in the lowest energy barrier in the rate-controlling step of the ethanol oxidation reaction (EOR), confirmed by density functional theory (DFT). The formation mechanism of PdCu NSAs and their excellent electrocatalytic activity toward EOR have been discussed and analyzed.

Mesoporous PdBi nanocages for enhanced electrocatalytic performances by all-direction accessibility and steric site activation

An effective yet simple approach was developed to synthesize mesoporous PdBi nanocages for electrochemical applications. This technique relies on the subtle utilization of the hydrolysis of a metal salt to generate precipitate cores in situ as templates for navigating the growth of mesoporous shells with the assistance of polymeric micelles. The mesoporous PdBi nanocages are then obtained by excavating vulnerable cores and regulating the crystals of mesoporous metallic skeletons. The resultant mesoporous PdBi nanocages exhibited excellent electrocatalytic performance toward the ethanol oxidation reaction with a mass activity of 3.56 A mg-1_Pd, specific activity of 17.82 mA cm-2 and faradaic efficiency of up to 55.69% for C1 products.

Alloyed Palladium-Lead Nanosheet Assemblies for Electrocatalytic Ethanol Oxidation

Synthesizing alloyed bimetallic electrocatalysts with a three-dimensional (3D) structure assembly have arouse great interests in electrocatalysis. We synthesized a class of alloyed Pd₃Pb/Pd nanosheet assemblies (NSAs) composed of a two-dimensional (2D) sheet structure with adjustable compositions via an oil bath approach at a low temperature. Both the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images reveal the successful formation of the nanosheet structure, where the morphology of Pd₃Pb/Pd NSAs can be regulated by adjusting the atomic mole ratio of Pb and Pb metal precursors. The power X-ray diffraction (XRD) pattern shows that Pd₃Pb/Pd NSA catalysts are homogeneously alloyed. Electrochemical analysis and the density functional theory (DFT) method demonstrate that the electrocatalytic activity of the alloyed Pd₃Pb/Pd NSAs can be improved by the doping of the Pb element. As a result of the addition of element Pb and change of the electron structure, the electrocatalytic activity toward ethanol oxidation of alloyed Pd₃Pb/Pd-15 NSA can reach up to 2886 mA mg^-1, which is approximately 2.8 times that of the pure Pd NSA counterpart (1020 mA mg^-1). The Pd₃Pb/Pd NSAs are favorable in a high catalytic temperature, high KOH concentration, and high ethanol concentration.

Atomically Isolated Rh Sites within Highly Branched Rh2 Sb Nanostructures Enhance Bifunctional Hydrogen Electrocatalysis

Breaking the bottleneck of hydrogen oxidation/evolution reactions (HOR/HER) in alkaline media is of tremendous importance for the development of anion exchange membrane fuel cells/water electrolyzers. Atomically dispersed active sites are known to exhibit excellent activity and selectivity toward diverse catalytic reactions. Here, a class of unique Rh₂ Sb nanocrystals with multiple nanobranches (denoted as Rh₂ Sb NBs) and atomically dispersed Rh sites are reported as promising electrocatalysts for alkaline HOR/HER. Rh₂ Sb NBs/C exhibits superior HER performance with a low overpotential and a small Tafel slope, outperforming both Rh NBs/C and commercial Pt/C. Significantly, Rh₂ Sb NBs show outstanding HOR performance of which the HOR specific activity and mass activity are about 9.9 and 10.1 times to those of Rh NBs/C, and about 4.2 and 3.7 times to those of Pt/C, respectively. Strikingly, Rh₂ Sb NBs can also exhibit excellent CO tolerance during HOR, whose activity can be largely maintained even at 100 ppm CO impurity. Density functional theory calculations reveal that the unsaturated Rh sites on Rh₂ Sb NBs surface are crucial for the enhanced alkaline HER and HOR activities. This work provides a unique catalyst design for efficient hydrogen electrocatalysis, which is critical for the development of alkaline fuel cells and beyond.

Construction of Pd-Zn dual sites to enhance the performance for ethanol electro-oxidation reaction

Rational design and synthesis of superior electrocatalysts for ethanol oxidation is crucial to practical applications of direct ethanol fuel cells. Here, we report that the construction of Pd-Zn dual sites with well exposure and uniformity can significantly improve the efficiency of ethanol electro-oxidation. Through synthetic method control, Pd-Zn dual sites on intermetallic PdZn nanoparticles, Pd-Pd sites on Pd nanoparticles and individual Pd sites are respectively obtained on the same N-doped carbon coated ZnO support. Compared with Pd-Pd sites and individual Pd sites, Pd-Zn dual sites display much higher activity for ethanol electro-oxidation, exceeding that of commercial Pd/C by a factor of ~24. Further computational studies disclose that Pd-Zn dual sites promote the adsorption of ethanol and hydroxide ion to optimize the electro-oxidation pathway with dramatically reduced energy barriers, leading to the superior activity. This work provides valuable clues for developing high-performance ethanol electro-oxidation catalysts for fuel cells.

Highly Porous Pt2Ir Alloy Nanocrystals as a Superior Catalyst with High-Efficiency C-C Bond Cleavage for Ethanol Electrooxidation

Achieving high catalytic performance with high CO₂ selectivity is critical for commercialization of direct ethanol fuel cells. Here, we report carbon-supported highly porous Pt₂Ir alloy nanocrystals (p-Pt₂Ir/C) for an ethanol oxidation reaction (EOR) that displays nearly 7.2-fold enhancement in mass activity and promotes antipoisoning ability and durability for the EOR as compared with the commercial Pt/C-JM. Moreover, the catalyst exhibits high CO₂ selectivity, 3.4-fold at 0.65 V (vs. SCE) and 4.1-fold at 0.75 V (vs. SCE) higher as compared with the carbon-supported porous Pt nanocrystals (p-Pt/C). The highly porous structure is composed of interconnected one-dimensional (1D) rough branches with an average diameter of only 1.9 nm, largely promoting Pt utilization efficiency and accelerating mass transfer. The 1D rough branch surface exposed many atomic steps/corners endowed with abundant high activity sites. Alloying with Ir can significantly improve the antipoisoning ability, durability, and C-C bond cleavage ability, thereby evidently enhancing its EOR performance.

Kinetically Controlled Synthesis of Rhodium Nanocrystals with Different Shapes and a Comparison Study of Their Thermal and Catalytic Properties

We report the synthesis of Rh nanocrystals with different shapes by controlling the kinetics involved in the growth of preformed Rh cubic seeds. Specifically, Rh nanocrystals with cubic, cuboctahedral, and octahedral shapes can all be obtained from the same cubic seeds under suitable reduction kinetics for the precursor. The success of such a synthesis also relies on the use of a halide-free precursor to avoid oxidative etching, as well as the involvement of a sufficiently high temperature to remove Br^- ions from the seeds while ensuring adequate surface diffusion. The availability of Rh nanocrystals with cubic and octahedral shapes allows for an evaluation of the facet dependences of their thermal and catalytic properties. The data from in situ electron microscopy studies indicate that the cubic and octahedral Rh nanocrystals can keep their original shapes up to 700 and 500 °C, respectively. When tested as catalysts for hydrazine decomposition, the octahedral nanocrystals exhibit almost 4-fold enhancement in terms of H₂ selectivity relative to the cubic counterpart. As for ethanol oxidation, the order is reversed, with the cubic nanocrystals being about three times more active than the octahedral sample.

A Tensile-Strained Pt-Rh Single-Atom Alloy Remarkably Boosts Ethanol Oxidation

The rational design and control of electrocatalysts at single-atomic sites could enable unprecedented atomic utilization and catalytic properties, yet it remains challenging in multimetallic alloys. Herein, the first example of isolated Rh atoms on ordered PtBi nanoplates (PtBi-Rh₁ ) by atomic galvanic replacement, and their subsequent transformation into a tensile-strained Pt-Rh single-atom alloy (PtBi@PtRh₁ ) via electrochemical dealloying are presented. Benefiting from the Rh₁ -tailored Pt (110) surface with tensile strain, the PtBi@PtRh₁ nanoplates exhibit record-high and all-round superior electrocatalytic performance including activity, selectivity, stability, and anti-poisoning ability toward ethanol oxidation in alkaline electrolytes. Density functional theory calculations reveal the synergism between effective Rh₁ and tensile strain in boosting the adsorption of ethanol and key surface intermediates and the CC bond cleavage of the intermediates. The facile synthesis of the tensile-strained single-atom alloy provides a novel strategy to construct model nanostructures, accelerating the development of highly efficient electrocatalysts.

Recent Advances in Amino-Based Molecules Assisted Control of Noble-Metal Electrocatalysts

Morphology-control synthesis is an effective means to tailor surface structure of noble-metal nanocrystals, which offers a sensitive knob for tuning their electrocatalytic properties. The functional molecules are often indispensable in the morphology-control synthesis through preferential adsorption on specific crystal facets, or controlling certain crystal growth directions. In this review, the recent progress in morphology-control synthesis of noble-metal nanocrystals assisted by amino-based functional molecules for electrocatalytic applications are focused on. Although a mass of noble-metal nanocrystals with different morphologies have been reported, few review studies have been published related to amino-based molecules assisted control strategy. A full understanding for the key roles of amino-based molecules in the morphology-control synthesis is still necessary. As a result, the explicit roles and mechanisms of various types of amino-based molecules, including amino-based small molecules and amino-based polymers, in morphology-control of noble-metal nanocrystals are summarized and discussed in detail. Also presented in this progress are unique electrocatalytic properties of various shaped noble-metal nanocrystals. Particularly, the optimization of electrocatalytic selectivity induced by specific amino-based functional molecules (e.g., polyallylamine and polyethyleneimine) is highlighted. At the end, some critical prospects, and challenges in terms of amino-based molecules-controlled synthesis and electrocatalytic applications are proposed.

Selective Ethanol Oxidation Reaction at the Rh-SnO2 Interface

Direct ethanol fuel cells (DEFCs) are regarded as an attractive power source with high energy density, bio-renewability, and convenient storage and transportation. However, the anodic reaction of DEFCs, that is, the ethanol oxidation reaction (EOR), suffers from poor efficiency due to the low selectivity to CO₂ (C1 pathway) and high selectivity to CH₃ COOH (C2 pathway). In this study, the selective EOR to CO₂ can be achieved at the Rh-SnO₂ interface in SnO₂ -Rh nanosheets (NSs). The optimized catalyst of 0.2SnO₂ -Rh NSs/C exhibits excellent alkaline EOR performance with a mass activity of 213.2 mA mg_Rh ^-1 and a Faraday efficiency of 72.8% for the C1 pathway, which are 1.7 and 1.9 times higher than those of Rh NSs/C. Mechanism studies indicate that the strong synergy at the Rh-SnO₂ interface significantly promotes the breaking of CC bond of C₂ H₅ OH to form CO₂ , and facilitates oxidation of the poisonous intermediates (^* CO and ^* CH₃ ) to suppress the deactivation of the catalyst. This work not only provides a highly selective, active, and stable catalyst for the EOR, but also promotes fundamental research for the design of efficient catalysts via interface modification.

A Phosphorus-Doped Ag@Pd Catalyst for Enhanced CC Bond Cleavage during Ethanol Electrooxidation

Ethanol is preferred to be oxidized into CO₂ for the construction of a high-performance direct ethanol fuel cell since this complete ethanol oxidation reaction (EOR) transfers 12 electrons. However, this EOR is sluggish and has the low activity as well as poor selectivity. To promote such a favorable EOR, more exactly the cleavage selectivity of CC bonds in ethanol, phosphorus-doped silver-core-and-Pd-shell catalysts (denoted as Ag@PdP) are designed and synthesized. In the alkaline media, a Ag@Pd₂ P_0.2 catalyst is superior toward EOR into CO₂ . It exhibits seven times higher mass activity and six times higher selectivity than the benchmark Pd/C catalyst. As confirmed by means of density functional theory calculation and in situ Fourier-transform infrared spectroscopy, such high performance stems from an increased adsorption energy of OH radicals on the Pd active sites. Meanwhile, the tensile strain effect of a core-shell structure of this Ag@Pd₂ P_0.2 catalyst favors the formation of adsorbed CH₃ CO intermediate, the key species for the enhanced C-C cleavage into CO₂ , instead of acetate. The proposed way to design and synthesize such high-performance EOR catalysts will explore the practical applications of direct alkaline ethanol fuel cells.

Shedding Light on the Role of Misfit Strain in Controlling Core-Shell Nanocrystals

Heteroepitaxial modification of nanomaterials has become a powerful means to create novel functionalities for various applications. One of the most elementary factors in heteroepitaxial nanostructures is the misfit strain arising from mismatched lattices of the constituent parts. Misfit strain not only dictates epitaxy kinetics for diversifying nanocrystal morphologies but also provides rational control over materials properties. In recent years, advances in chemical synthesis along with the rapid development of electron microscopy and X-ray diffraction techniques have enabled a substantial understanding of strain-related processes, which offers theoretical foundation and experimental guidance for researchers to refine heteroepitaxial nanostructures and their properties. Herein, recent investigations on heterogeneous core-shell nanocrystals containing misfit strains are summarized, with a focus on the mechanistic understanding of strain and strain-induced effects such as tuning the epitaxial habit, modulating the optical emission, and enhancing the catalytic activity and magnetic coercivity.

Kinetically Manipulating the Nucleus Attachment to Create Atypical Defective Rh-Pt Alloyed Nanostructures as Active Electrocatalysts

Defective metal nanostructures have attracted great attention due to the striking catalytic behavior of the defect sites. Atypical metal nanocrystals generated from attached nuclei can accommodate abundant grain boundaries (GBs) and twin boundaries (TBs). However, the understanding of their growth-mechanism and precisely synthetic control over such defective nanocrystals are still scarce. Herein, using the Rh-Pt nanoalloy as a model system, we systematically demonstrate that a prudent control of the reaction kinetics can manipulate the metal nucleation and nucleus attachment to create atypical nanocrystals, including small isolated nanoparticles (NPs), defect-rich wavy nanowires (WNWs), and {100} facet-bounded spliced nanocubes (SNCs). In the ethanol oxidation electrocatalysis, the Rh₄₇ Pt₅₃ WNWs featured with abundant TBs and GBs show the greatest mass activity (0.655 A ⋅ mg^-1 _Pt , 2.9 times to the commercial Pt/C) and durability. Our work captures the core of reaction kinetics on regulating the nucleus attachment and enables the rational control over the nanocrystal morphology and defect.

Ethanol Electrooxidation on Rhodium-Lead Catalysts in Alkaline Media: High Mass Activity, Long-Term Durability, and Considerable CO2 Selectivity

Rhodium (Rh)-based catalysts may solve the long-standing inefficient oxidation of ethanol for direct ethanol fuel cells (DEFCs); however, the performance of ethanol oxidation reaction (EOR) on existing Rh-based catalysts are far limited. Herein, the Rh-Pb catalysts are synthesized by building Pb and Pb oxide around Rh nanodomain, which shows highly efficient splitting CC bond and facile further oxidation of as-generated C1 intermediates (CO_ad and CH_x fragments). It exhibits an ever-highest EOR peak mass activity of ≈2636 mA mg^-1 _Rh among Rh-based catalysts in alkaline media. Meanwhile, its anodic current remains ≈50% even after a 4 h durability test at 0.53 V versus RHE. As for the C1-pathway selectivity, in situ infrared adsorption spectral (IRAS) results demonstrate that it could significantly improve the production of CO₂ . More directly, the apparent faraday efficiency of EOR C1 pathway is estimated to be as high as 20% (at 0.53 V versus RHE). This Rh-Pb catalyst could hold great promise for developing the commercial DEFCs.

Density Functional Theoretical Study on the Electronic Structure of Rh2O7 + with Low Oxidation States

Rh₂O _n ⁺ (n = 2-10) species are prepared by the reaction of the laser-ablated rhodium atoms with oxygen; furthermore, they are characterized by employing time-of-flight mass spectroscopy. To reveal the stable electronic structure, in this study, we performed the density functional theory calculations for the possible isomers of Rh₂O₇ ⁺. A total of 29 geometries were obtained including cyclic Rh₂O₃, cyclic Rh₂O₂, and ring-opening structures with doublet, quartet, sextet, and octet states. It is noteworthy that no Rh-Rh bond was observed for all the optimized Rh₂O₇ ⁺ isomers including oxides, peroxides, superoxides, and oxygen groups. The optimized geometries were also confirmed to exhibit minimum structural energies by employing harmonic frequency analysis at the same energy level. Generally, two types of oxygen-bridged geometries were discovered with cyclic and pseudo-linear Rh₂O₇ ⁺, which contained one or more than one O₂ groups. It is concluded that the cyclic structure comprises a lower energy than that observed in pseudo-linear structures. In addition, Rh₂O₇ ⁺ tends to be unstable when the coordination groups change from O₂ to O₂ ^- unit. Finally, the localized orbital bonding analysis indicates that Rh has oxidation states of 1 or 2 in cyclic Rh₂O₇ ⁺ structures; this is true even in the presence of O^2-, O₂ ^-, and O₂ ^2- groups.

Edge Enrichment of Ultrathin 2D PdPtCu Trimetallic Nanostructures Effectuates Top-Ranked Ethanol Electrooxidation

Atomic edge sites on two-dimensional (2D) nanomaterials display striking catalytic behavior, whereas edge engineering for 2D metal nanocatalysts remains an insurmountable challenge. Here we advance a one-pot synthesis of ultrathin 2D PdPtCu trimetallic nanosheets and nanorings with escalating low-coordinated edge proportions from 11.74% and 23.11% to 45.85% as cutting-edge ethanol oxidation reaction (EOR) electrocatalysts. This in situ edge enrichment hinges on a competitive surface capping and etching strategy with integrated manipulation of the reaction kinetics. Electrocatalysis tests demystify an edge-relied EOR performance, where the edge-richest 9.0 nm-Pd₆₁Pt₂₂Cu₁₇ nanorings attain an exceptional activity (12.42 A mg^-1_Pt+Pd, 20.2 times that of commercial Pt/C) with substantially improved durability. Molecularly mechanistic studies certify that the unsaturated edge sites on these 2D catalysts prevail, triggering the C-C bond scission and succeeding CO removal to facilitate a 12-electron-transferring EOR process. This study introduces the "metal-edge-driven" concept and enables the "edge sites on 2D multimetallic nanocatalysts" technique to design versatile heterocatalysts.

Integrating Rh Species with NiFe-Layered Double Hydroxide for Overall Water Splitting

NiFe-layered double hydroxide (LDH) is thought of as a promising bifunctional water-splitting catalyst, owing to its excellent performances for alkaline oxygen evolution reactions (OERs). However, it shows extremely poor activity toward hydrogen evolution reactions (HERs) due to the weak hydrogen adsorption. We demonstrated that the integration of Rh species and NiFe-LDH can dramatically improve its HER kinetics without sacrificing the OER performance. The Rh species were initially integrated into NiFe-LDH as oxidized dopants and metallic clusters (< 1 nm). In 1 M KOH electrolyte, an overpotential of 58 mV is needed to catalyze 10 mA cm^-2 HER current density. Furthermore, this catalyst only requires 1.46 V to drive an electrolyzer at 10 mA cm^-2. A strong interaction between metallic Rh clusters and NiFe hydroxide during the HER process is revealed. The theoretical calculation shows the Rh ions replace Fe ions as the major active sites that are responsible for OERs.

Pore structure dependent activity and durability of mesoporous rhodium nanoparticles towards the methanol oxidation reaction

A significant porous structure effect of mesoporous rhodium nanoparticles on the electrocatalytic methanol oxidation reaction was reported.

Cyanogel auto-reduction induced synthesis of PdCo nanocubes on carbon nanobowls: a highly active electrocatalyst for ethanol electrooxidation

Direct ethanol fuel cells (DEFCs) with a high conversion efficiency are quite promising candidates for energy conversion devices. Herein, we have successfully synthesized PdCo alloy nanocubes supported on carbon nanobowl (denoted as Pd₂Co₁/CNB) nanohybrids by using the cyanogel auto-reduction method at high temperature. The morphology, composition and structure of Pd₂Co₁/CNB nanohybrids are characterized in detail, revealing that PdCo nanocubes have a high alloying degree and special {110} facets. In cyclic voltammetry measurements, Pd₂Co₁/CNB nanohybrids show a mass activity of 1089.0 A g _Pd^-1 and a specific activity of 40.03 mA cm^-2 for ethanol electrooxidation at peak potential, which are much higher than that of the commercial Pd/C electrocatalyst (278.2 A g_Pd^-1 and 8.22 mA cm^-2). Additionally, chronoamperometry measurements show that Pd₂Co₁/CNB nanohybrids have excellent durability for ethanol electrooxidation. A high alloying degree, special {110} facets and the CNB supporting material contribute to the high activity and durability of Pd₂Co₁/CNB nanohybrids, making them a highly promising Pt-alternative electrocatalyst for ethanol electrooxidation in DEFCs.