Atomically deviated Pd-Te nanoplates boost methanol-tolerant fuel cells

Tuning Crystal Phase of Palladium-Selenium Nanowires for Enhanced Ethylene Glycol Electrocatalytic Oxidation

Alcohol electrooxidation is pivotal for a sustainable energy economy. However, designing efficient electrocatalysts for this process is still a formidable challenge. Herein, palladium-selenium nanowires featuring distinct crystal phases: monoclinic Pd7Se2 and tetragonal Pd4.5Se for ethylene glycol electrooxidation reaction (EGOR) are synthesized. Notably, the supported monoclinic Pd7Se2 nanowires (m-Pd7Se2 NWs/C) exhibit superior EGOR activity, achieving a mass activity (MA) and specific activity (SA) of 10.4 A mgPd -1 (18.7 mA cm-2), which are 8.0 (6.7) and 10.4 (8.2) times versus the tetragonal Pd4.5Se and commercial Pd/C and surpass those reported in the literature. Furthermore, m-Pd7Se2 NWs/C displays robust catalytic activity for other alcohol electrooxidation. Comprehensive characterization and density functional theory (DFT) calculations reveal that the enhanced electrocatalytic performance is attributed to the increased formation of Pd0 on the high-index facets of the m-Pd7Se2 NWs, which lowers the energy barriers for the C─C bond dissociation in CHOHCHOH* and the CO* oxidation to CO2*. This study provides palladium-based alloy electrocatalysts exhibiting the highest mass activity reported to date for the electrooxidation of ethylene glycol, achieved through the crystalline phase engineering strategy.

Phosphorus-Doping Enables the Superior Durability of a Palladium Electrocatalyst towards Alkaline Oxygen Reduction Reactions

The sluggish kinetics of oxygen reduction reactions (ORRs) require considerable Pd in the cathode, hindering the widespread of alkaline fuel cells (AFCs). By alloying Pd with transition metals, the oxygen reduction reaction's catalytic properties can be substantially enhanced. Nevertheless, the utilization of Pd-transition metal alloys in fuel cells is significantly constrained by their inadequate long-term durability due to the propensity of transition metals to leach. In this study, a nonmetallic doping strategy was devised and implemented to produce a Pd catalyst doped with P that exhibited exceptional durability towards ORRs. Pd3P0.95 with an average size of 6.41 nm was synthesized by the heat-treatment phosphorization of Pd nanoparticles followed by acid etching. After P-doping, the size of the Pd nanoparticles increased from 5.37 nm to 6.41 nm, and the initial mass activity (MA) of Pd3P0.95/NC reached 0.175 A mgPd-1 at 0.9 V, slightly lower than that of Pd/C. However, after 40,000 cycles of accelerated durability testing, instead of decreasing, the MA of Pd3P0.95/NC increased by 6.3% while the MA loss of Pd/C was 38.3%. The durability was primarily ascribed to the electronic structure effect and the aggregation resistance of the Pd nanoparticles. This research also establishes a foundation for the development of Pd-based ORR catalysts and offers a direction for the future advancement of catalysts designed for practical applications in AFCs.

Eggshell-Like Carbon Microspheres with Curvature Scheme: Distorted Energy Band and Atomic Charge Waves-Driven High Performance for Zinc-Air Battery

A metal-free nanocarbon with an eggshell structure is synthesized from chitosan (CS) and natural spherical graphite (NSG) as a cathode electrocatalyst for clean zinc-air batteries and fuel cells. It is developed using CS-derived carbons as an eggshell, covering NSG cores. The synthesis involves the in situ growth of CS on NSG, followed by ammonia-assisted pyrolysis for carbonization. The resulting catalyst displays a curved structure and completely coated NSG, showing superior oxygen reduction reaction (ORR) performance. In 1 M NaOH, the ORR half-wave potential reached 0.93 V, surpassing the commercial Pt/C catalyst by 50 mV. Furthermore, a zinc-air battery featuring the catalyst achieves a peak power density of 167 mW cm-2 with excellent stability, outperforming the Pt/C. The improved performance of the eggshell carbons can be attributed to the distorted energy band of the active sites in the form of N-C moieties. More importantly, the curved thin eggshells induce built-in electric fields that can promote electron redistribution to generate atomic charge waves around the N-C moieties on the carbon shells. As a result, the high positively charged and stable C+ sites adjacent to N atoms optimize the adsorption strength of oxygen molecules, thereby facilitating performance.

Surface-Enriched Single-Bi-Atoms Tailoring of Pt Nanorings for Direct Methanol Fuel Cells with Ultralow-Pt-Loading

Single-atom decorating of Pt emerges as a highly effective strategy to boost catalytic properties, which can trigger the most Pt active sites while blocking the smallest number of Pt atoms. However, the rational design and creation of high-density single-atoms on Pt surface remain as a huge challenge. Herein, a customized synthesis of surface-enriched single-Bi-atoms tailored Pt nanorings (SE-Bi1/Pt NRs) toward methanol oxidation is reported, which is guided by the density functional theory (DFT) calculations suggesting that a relatively higher density of Bi species on Pt surface can ensure a CO-free pathway and accelerate the kinetics of *HCOOH formation. Decorating Pt NRs with dense single-Bi-atoms is achieved by starting from PtBi intermetallic nanoplates (NPs) with intrinsically isolated Bi atoms and subsequent etching and annealing treatments. The SE-Bi1/Pt NRs exhibit a mass activity of 23.77 A mg-1 Pt toward methanol oxidation in alkaline electrolyte, which is 2.2 and 12.8 times higher than those of Pt-Bi NRs and Pt/C, respectively. This excellent activity endows the SE-Bi1/Pt NRs with a high likelihood to be used as a practical anodic electrocatalyst for direct methanol fuel cells （DMFCs） with high power density of 85.3 mW cm-2 and ultralow Pt loading of 0.39 mg cm-2.

Modulating Electronic Structure and Atomic Insights into the Novel Hierarchically Porous PdCuFe Trimetallic Alloy Aerogel for Efficient Oxygen Reduction

The high cost of noble Pd/Pt required for the oxygen reduction reaction (ORR) in the cathode restricts the wide applications of fuel cells. In this study, the synthesis of a novel Pd3CuFe0.5 aerogel electrocatalyst is successfully demonstrated using self-assembly and lyophilization techniques, employing a mild reducing agent. The resulting aerogel electrocatalyst exhibits a distinctive 3D network structure, possessing a substantial BET-specific surface area of 75.19 m2 g-1. It is worth noting that the optimized Pd3CuFe0.5 aerogel demonstrates exceptional ORR performance with a high half-wave potential of 0.92 V versus RHE, a significant limiting current density of 7.6 mA cm-2, and the excellent electrocatalytic stability, superior to the reported noble metal electrocatalysts, with the ORR activity decays only 4.9% after 16 000 s. In addition, the Pd3CuFe0.5 aerogel electrocatalyst shows superior cycling stability for ≈120 h at a charge/discharge current density of 10 mA cm-2, indicating its promising application in fuel cells. Furthermore, the resulting composite aerogel possesses excellent hydrogen evolution reaction and ethanol oxidation reaction activity. The density functional theory calculations show that the partial oxidation of Pd3CuFe0.5 aerogel leads to a negative shift of the d-band center, which energetically optimizes the binding strength of *O intermediates, therefore accelerating the ORR activity.

Mixed-Dimensional Partial Dealloyed PtCuBi/C as High-Performance Electrocatalysts for Methanol Oxidation with Enhanced CO Tolerance

Developing efficient electrocatalysts for methanol oxidation reaction (MOR) is crucial in advancing the commercialization of direct methanol fuel cells (DMFCs). Herein, carbon-supported 0D/2D PtCuBi/C (0D/2D PtCuBi/C) catalysts are fabricated through a solvothermal method, followed by a partial electrochemical dealloying process to form a novel mixed-dimensional electrochemically dealloyed PtCuBi/C (0D/2D D-PtCuBi/C) catalysts. Benefiting from distinctive mixed-dimensional structure and composition, the as-obtained 0D/2D D-PtCuBi/C catalysts possess abundant accessible active sites. The introduction of Cu as a water-activating element weakens the COads, and oxophilic metal Bi facilitates the OHads, thereby enhancing its tolerance to CO poisoning and promoting MOR activity. The X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure spectroscopy (XAFS) collectively reveal the electron transfer from Cu and Bi to Pt, the electron-enrichment effect induced by dealloying, and the strong interactions among Pt-M (Cu, Pt, and Bi) multi-active sites, which improve the tuning of the electronic structure and enhancement of electron transfer ability. Impressively, the optimized 0D/2D D-PtCuBi/C catalysts exhibit the superior mass activity (MA) of 17.68 A mgPt -1 for MOR, which is 14.86 times higher than that of commercial Pt/C. This study offers a proposed strategy for Pt-based alloy catalysts, enabling their use as efficient anodic materials in fuel cell applications.

Lattice-Strained Metallic Aerogels as Efficient and Anti-Poisoning Electrocatalysts for Oxygen Reduction Reaction

Lattice strain engineering optimizes the interaction between the catalytic surface and adsorbed molecules. This is done by adjusting the electron and geometric structure of the metal site to achieve high electrochemical performance, but, to date, it has been rarely reported on anti-poisoned oxygen reduction reaction (ORR). Herein, lattice-strained Pd@PdBiCo quasi core-shell metallic aerogels (MAs) were designed by "one-pot and two-step" method for anti-poisoned ORR. Pd@PdBiCo MAs/C maintain their original activity (1.034 A mgPd -1 ) in electrolytes with CH3 OH and CO at 0.85 V vs. reversible hydrogen electrode (RHE), outperforming the commercial Pd/C (0.156 A mgPd -1 ), Pd MAs/C (0.351 A mgPd -1 ), and PdBiCo MAs/C (0.227 A mgPd -1 ). Moreover, Pd@PdBiCo MAs/C also show high stability and anti-poisoning with negligible activity decay after 8000 cycles in 0.1 m KOH+0.3 m CH3 OH. These results of X-ray photoelectron spectroscopy, CO stripping, and diffuses reflectance FTIR spectroscopy reveal that the tensile strain and strong interaction between different elements of Pd@PdBiCo MAs/C effectively optimize the electronic structure to promote O2 adsorption and activation, while suppressing CH3 OH oxidation and CO adsorption, leading to high ORR activity and anti-poisoning property. This work inspires the rational design of MAs in fuel cells and beyond.

Metal nitrides for seawater electrolysis

Electrocatalytic high-throughput seawater electrolysis for hydrogen production is a promising green energy technology that offers possibilities for environmental and energy sustainability. However, large-scale application is limited by the complex composition of seawater, high concentration of Cl- leading to competing reaction, and severe corrosion of electrode materials. In recent years, extensive research has been conducted to address these challenges. Metal nitrides (MNs) with excellent chemical stability and catalytic properties have emerged as ideal electrocatalyst candidates. This review presents the electrode reactions and basic parameters of the seawater splitting process, and summarizes the types and selection principles of conductive substrates with critical analysis of the design principles for seawater electrocatalysts. The focus is on discussing the properties, synthesis, and design strategies of MN-based electrocatalysts. Finally, we provide an outlook for the future development of MNs in the high-throughput seawater electrolysis field and highlight key issues that require further research and optimization.

Nanoscale Metal Particle Modified Single-Atom Catalyst: Synthesis, Characterization, and Application

Single-atom catalysts (SACs) have attracted considerable attention in heterogeneous catalysis because of their well-defined active sites, maximum atomic utilization efficiency, and unique unsaturated coordinated structures. However, their effectiveness is limited to reactions requiring active sites containing multiple metal atoms. Furthermore, the loading amounts of single-atom sites must be restricted to prevent aggregation, which can adversely affect the catalytic performance despite the high activity of the individual atoms. The introduction of nanoscale metal particles (NMPs) into SACs (NMP-SACs) has proven to be an efficient approach for improving their catalytic performance. A comprehensive review is urgently needed to systematically introduce the synthesis, characterization, and application of NMP-SACs and the mechanisms behind their superior catalytic performance. This review first presents and classifies the different mechanisms through which NMPs enhance the performance of SACs. It then summarizes the currently reported synthetic strategies and state-of-the-art characterization techniques of NMP-SACs. Moreover, their application in electro/thermo/photocatalysis, and the reasons for their superior performance are discussed. Finally, the challenges and perspectives of NMP-SACs for the future design of advanced catalysts are addressed.

Plasma-Induced Formation of Pt Nanoparticles with Optimized Surface Oxidation States for Methanol Oxidation and Oxygen Reduction Reactions to Achieve High-Performance DMFCs

Plasma treatment and reduction are used to synthesize Pt nanoparticles (NPs) on nitrogen-doped carbon nanotubes (p-Pt/p-NCNT) with a low Pt content. In particular, the plasma treatment is used to treat the NCNT to give it with more surface defects, facilitating a better growth of the Pt NPs, while the plasma reduction produces the Pt NPs with a reduced fraction of the surface atoms at the high oxidation states, increasing the catalytic activities of the p-Pt@p-NCNT. Even at the low Pt content (7.8 wt.%), the p-Pt@p-NCNT shows superior catalytic activities and good stabilities for methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). The density functional theory (DFT) calculations indicate that the defects generated in the plasma treatment can help the growth of the Pt NPs on the NCNTs, leading to the stronger electronic coupling between Pt and NCNT and the increased stability of the catalyst. The plasma reduction can give the Pt NPs with optimized surface oxidation states, decreasing the energy barriers of the rate-determining steps for MOR and ORR. When used as the anode and cathode catalysts for the direct methanol fuel cells (DMFCs), the p-Pt@p-NCNT exhibits a higher maximum power density of 81.9 mW cm-2  at 80 °C and shows good durability.

Porous, Ultrathin PtAgBiTe Nanosheets for Direct Hydrazine Hydrate Fuel Cell Devices

Ultrathin 2D nanomaterials have attracted extensive attention due to their fascinating applications in sustainable and clean-energy-related devices, but obtaining ultrathin 2D multimetallic polycrystalline structures with large lateral dimensions remains a challenge. In this study, ultrathin 2D porous PtAgBiTe and PtBiTe polycrystalline nanosheets (PNSs) are obtained via a visible-light-photoinduced Bi2 Te3 -nanosheet-mediated route. The PtAgBiTe PNSs are assembled by sub-5 nm grains with widths beyond 700 nm. Strain and ligand effects originating from the porous, curly polycrystalline structure endow the PtAgBiTe PNSs with robust hydrazine hydrate oxidation reaction activity. Theoretical research demonstrates that the modified Pt activates the N-H bonds in N2 H4 during the reaction, and strong hybridization between Pt-5d and N-2p facilitates dehydrogenation while reducing energy consumption. The peak power densities of the PtAgBiTe PNSs in actual hydrazine-O2 /air fuel cell devices are boosted to 532.9/315.9 mW cm-2 , while those of the commercial Pt/C are 394.7/157.9 mW cm-2 . This work provides a strategy not only for preparing ultrathin multimetallic PNSs but also for finding promising electrocatalysts for actual hydrazine fuel cells.

Bimetallic Nanoalloy Catalysts for Green Energy Production: Advances in Synthesis Routes and Characterization Techniques

Bimetallic Nanoalloy catalysts have diverse uses in clean energy, sensing, catalysis, biomedicine, and energy storage, with some supported and unsupported catalysts. Conventional synthetic methods for producing bimetallic alloy nanoparticles often produce unalloyed and bulky particles that do not exhibit desired characteristics. Alloys, when prepared with advanced nanoscale methods, give higher surface area, activity, and selectivity than individual metals due to changes in their electronic properties and reduced size. This review demonstrates the synthesis methods and principles to produce and characterize highly dispersed, well-alloyed bimetallic nanoalloy particles in relatively simple, effective, and generalized approaches and the overall existence of conventional synthetic methods with modifications to prepare bimetallic alloy catalysts. The basic concepts and mechanistic understanding are represented with purposely selected examples. Herein, the enthralling properties with widespread applications of nanoalloy catalysts in heterogeneous catalysis are also presented, especially for Hydrogen Evolution Reaction (HER), Oxidation Reduction Reaction (ORR), Oxygen Evolution Reaction (OER), and alcohol oxidation with a particular focus on Pt and Pd-based bimetallic nanoalloys and their numerous fields of applications. The high entropy alloy is described as a complicated subject with an emphasis on laser-based green synthesis of nanoparticles and, in conclusion, the forecasts and contemporary challenges for the controlled synthesis of nanoalloys are addressed.

Bismuth Incorporation in Palladium Hydride for the Electrocatalytic Ethanol Oxidation with Enhanced CO Tolerance

Introducing nonmetal and oxophilic metal into palladium (Pd)-based catalysts is beneficial for boosting electrocatalysis, especially regarding the improvement of mass activity (MA) and CO tolerance. Herein, the stable bismuth-doped palladium hydride (Bi/PdH) networks have been successfully fabricated through a simple one-step method. The intercalation of interstitial H atoms expands the lattice of Pd, and the doping of oxophilic metal Bi restrains the adsorption of poisonous intermediates on the surface of Pd, thereby improving the activity and durability of the as-prepared catalysts in the ethanol oxidation reaction (EOR). The obtained Bi/PdH networks manifest a remarkable MA of 8.51 A·mgPd-1, which is 11.18 times higher than that of commercial Pd/C (0.76 A·mgPd-1). The CO-stripping analysis results indicate that Bi doping can significantly prohibit CO adsorption on the surface of the Bi/PdH networks. The density functional theory (DFT) calculations also reveal that Bi doping enhances the OH* adsorption on the catalyst surface and mitigates the interaction between Pd and CO* intermediates, providing deeper insights into the origin of the enhanced EOR activity and CO tolerance. This work describes an impactful path for producing high-performance and durable PdH-based nanocatalysts.

Sub-Monolayer SbOx on PtPb/Pt Nanoplate Boosts Direct Formic Acid Oxidation Catalysis

To promote the commercialization of direct formic acid fuel cell (DFAFC), it is vital to explore new types of direct formic acid oxidation (FAOR) catalysts with high activity and direct pathway. Here, we report the synthesis of intermetallic platinum-lead/platinum nanoplates inlaid with sub-monolayer antimony oxide surface (PtPb/Pt@sub-SbOx NPs) for efficient catalytic applications in FAOR. Impressively, they can achieve the remarkable FAOR specific and mass activities of 28.7 mA cm-2 and 7.2 A mgPt-1, which are 151 and 60 times higher than those of the state-of-the-art commercial Pt/C, respectively. Furthermore, the X-ray photoelectron spectroscopy and X-ray absorption spectroscopy results collectively reveal the optimization of the local coordination environment by the surface sub-monolayer SbOx, along with the electron transfer from Pb and Sb to Pt, driving the predominant dehydrogenation process. The sub-monolayer SbOx on the surface can effectively attenuate the CO generation, largely improving the FAOR performance of PtPb/Pt@sub-SbOx NPs. This work develops a class of high-performance Pt-based anodic catalyst for DFAFC via constructing the unique intermetallic core/sub-monolayer shell structure.

Coordination Engineering of Dual Co, Ni Active Sites in N-Doped Carbon Fostering Reversible Oxygen Electrocatalysis

The development of affordable and non-noble-metal-based reversible oxygen electrocatalysts is required for renewable energy conversion and storage systems like metal-air batteries (MABs). However, the nonbifunctionality of most of the catalysts impedes their use in rechargeable MAB applications. Moreover, the loss of active sites also affects the long-term performance of the electrocatalyst toward oxygen electrocatalysis. In this work, we report a simplistic yet controllable chemical approach for the synthesis of dual transitional metals such as cobalt, nickel, and nitrogen-doped carbon (CoNi-NC) as bifunctional electrode materials for rechargeable zinc-air batteries (ZABs). The spatially isolated Ni-N4 and Co-N4 active units were rendered for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively. The individual efficacy of both reversible reactions enables an ΔE value of ∼0.72 V, which outperforms several bifunctional electrocatalysts reported in the literature. The half-wave potential (E1/2) and overpotential were achieved at 0.83 V and 330 mV (vs RHE) for ORR and OER, respectively. The peak power density of ZAB equipped with the CoNi-NC catalyst was calculated to be 194 mW cm-2. The present strategy for the synthesis of bifunctional electrocatalysts with dual active sites offers prospects for developing electrochemical energy storage and conversion systems.

Platinum-Lead-Bismuth/Platinum-Bismuth Core/Shell Nanoplate Achieves Complete Dehydrogenation Pathway for Direct Formic Acid Oxidation Catalysis

Designing platinum (Pt)-based formic acid oxidation reaction (FAOR) catalysts with high performance and high selectivity of direct dehydrogenation pathway for direct formic acid fuel cell (DFAFC) is desirable yet challenging. Herein, we report a new class of surface-uneven PtPbBi/PtBi core/shell nanoplates (PtPbBi/PtBi NPs) as the highly active and selective FAOR catalysts, even in the complicated membrane electrode assembly (MEA) medium. They can achieve unprecedented specific and mass activities of 25.1 mA cm^-2 and 7.4 A mg_Pt^-1 for FAOR, 156 and 62 times higher than those of commercial Pt/C, respectively, which is the highest for a FAOR catalyst by far. Simultaneously, they show highly weak adsorption of CO and high dehydrogenation pathway selectivity in the FAOR test. More importantly, the PtPbBi/PtBi NPs can reach the power density of 161.5 mW cm^-2, along with a stable discharge performance (45.8% decay of power density at 0.4 V for 10 h), demonstrating great potential in a single DFAFC device. The in situ Fourier transform infrared spectroscopy (FTIR) and X-ray absorption spectroscopy (XAS) results collectively reveal a local electron interaction between PtPbBi and PtBi. In addition, the high-tolerance PtBi shell can effectively inhibit the production/adsorption of CO, resulting in the complete presence of the dehydrogenation pathway for FAOR. This work demonstrates an efficient Pt-based FAOR catalyst with 100% direct reaction selectivity, which is of great significance for driving the commercialization of DFAFC.

A universal synthesis of ultrathin Pd-based nanorings for efficient ethanol electrooxidation

Metallic nanorings (NRs) with open hollow structures are of particular interest in energy-related catalysis due to their unique features, which include the high utilization of active sites and facile accessibility for reactants. However, there is still a lack of general methods for synthesizing Pd-based multimetallic NRs with a high catalytic performance. Herein, we develop a template-directed strategy for the synthesis of ultrathin PdM (M = Bi, Sb, Pb, BiPb) NRs with a tunable size. Specifically, ultrathin Pd nanosheets (NSs) are used as a template to steer the deposition of M atoms and the interatomic diffusion between Pd and M, subsequently resulting in the hollow structured NRs. Taking the ethanol oxidation reaction (EOR) as a proof-of-concept application, the PdBi NRs deliver a substantially improved activity relative to the Pd NSs and commercial Pd/C catalysts, simultaneously showing outstanding stability and CO tolerance. Mechanistically, density functional theory (DFT) calculations disclose that the incorporation of Bi reduces the energy barrier of the rate-determining step in the EOR C₂-path, which, together with the high ratio of exposed active sites, endows the PdBi NRs with an excellent EOR activity. We believe that our work can illuminate the general synthesis of multimetallic NRs and the rational design of advanced electrocatalysts.

Two-dimensional template-directed synthesis of one-dimensional kink-rich Pd3Pb nanowires for efficient oxygen reduction

Developing facile synthetic strategies toward ultrafine one-dimensional (1D) nanowires (NWs) with rich catalytic hot spots is pivotal for exploring effective heterogeneous catalysts. Herein, we demonstrate a two-dimensional (2D) template-directed strategy for synthesizing 1D kink-rich Pd₃Pb NWs with abundant grain boundaries to serve as high-efficiency electrocatalysts toward oxygen reduction reaction (ORR). In this one-pot synthesis, ultrathin Pd nanosheets were initially generated, which then served as self-sacrificial 2D nano-templates. A dynamic equilibrium growth was subsequently established on the 2D Pd nanosheets through the center-selected etching of Pd atoms and edge-preferred co-deposition of Pd/Pb atoms. This was followed by the oriented attachment of the generated Pd/Pb alloy nanograins and fragments. Thus, kink-rich Pd₃Pb NWs with rich grain boundary defects were obtained in high yield, and these NWs were used as electrocatalytic active catalysts. The surface electronic interaction between Pd and Pb atoms effectively decreased the surface d-band center to weaken the binding of oxygen-containing intermediates toward improved ORR kinetics. Specifically, the kink-rich Pd₃Pb NWs/C catalyst delivered outstanding ORR mass activity and specific activity (2.26 A⋅mg_Pd^-1 and 2.59 mA⋅cm^-2, respectively) in an alkaline solution. These values were respectively 13.3 and 10.8 times those of state-of-the-art commercial Pt/C catalyst. This study provides an innovative strategy for fabricating defect-rich low-dimensional nanocatalysts for efficient energy conversion catalysis.

Ultrafine Core@Shell Cu1Au1@Cu1Pd3 Nanodots Synergized with 3D Porous N-Doped Graphene Nanosheets as a High-Performance Multifunctional Electrocatalyst

Rationally combining designed supports and metal-based nanomaterials is effective to synergize their respective physicochemical and electrochemical properties for developing highly active and stable/durable electrocatalysts. Accordingly, in this work, sub-5 nm and monodispersed nanodots (NDs) with the special nanostructure of an ultrafine Cu₁Au₁ core and a 2-3-atomic-layer Cu₁Pd₃ shell are synthesized by a facile solvothermal method, which are further evenly and firmly anchored onto 3D porous N-doped graphene nanosheets (NGS) via a simple annealing (A) process. The as-obtained Cu₁Au₁@Cu₁Pd₃ NDs/NGS-A exhibits exceptional electrocatalytic activity and noble-metal utilization toward the alkaline oxygen reduction, methanol oxidation, and ethanol oxidation reactions, showing dozens-fold enhancements compared with commercial Pd/C and Pt/C. Besides, it also has excellent long-term electrochemical stability and electrocatalytic durability. Advanced and comprehensive experimental and theoretical analyses unveil the synthetic mechanism of the special core@shell nanostructure and further reveal the origins of the significantly enhanced electrocatalytic performance: (1) the prominent structural properties of NGS, (2) the ultrasmall and monodispersed size as well as the highly uniform morphology of the NDs-A, (3) the special Cu-Au-Pd alloy nanostructure with an ultrafine core and a subnanometer shell, and (4) the strong metal-support interaction. This work not only develops a facile method for fabricating the special metal-based ultrafine-core@ultrathin-shell nanostructure but also proposes an effective and practical design paradigm of comprehensively and rationally considering both supports and metal-based nanomaterials for realizing high-performance multifunctional electrocatalysts, which can be further expanded to other supports and metal-based nanomaterials for other energy-conversion or environmental (electro)catalytic applications.

Introducing Te for boosting electrocatalytic reactions

The deployment of robust catalysts for electrochemical reactions is a critical topic for energy conversion techniques. Te-based nanomaterials have attracted increasing attention for their application in electrochemical reactions due to their positive influence on the electrocatalytic performance induced by their distinctive electronic and physicochemical properties. Herein, we have summarized the recent progress on Te-based nanocatalysts for electrocatalytic reactions by primarily focusing on the positive influence of Te on electrocatalysts. Firstly, Te-based nanomaterials can serve as an ideal template for the construction of well-defined nanostructures. Secondly, Te doping can significantly modify the electronic structure of the host catalyst, thereby, leading to the optimization of binding strength with intermediates. Furthermore, the Te etching strategy can also create a high density of surface defects, thereby leading to substantial improvement in the electrocatalytic performance. Additionally, many representative Te-based nanocatalysts for electrocatalytic reactions are also summarized and systematically discussed. Finally, a conclusive and perspective discussion is also provided to provide guidance for the future development of more efficient electrocatalysts.

Advances in platinum-based and platinum-free oxygen reduction reaction catalysts for cathodes in direct methanol fuel cells

Direct methanol fuel cells (DMFCs) have been the focus of future research because of their simple structure, abundant fuel sources, high energy conversion efficiency and low cost. Among the components in DMFC, the activity and stability of the cathode catalyst is the key to the performance and lifetime of the DMFCs. Oxygen reduction reaction (ORR) is an important electrode reaction on DMFC cathode. It is known that Pt is widely used in the fabrication of ORR catalysts, but the limited earth storage of Pt and its high price limit the use of Pt-based commercial catalysts in DMFCs. To overcome these problems, advances have been made on new low Pt-based catalysts and Pt-free catalysts in recent years. In this article, the development of novel ORR catalysts and the carbon supports is reviewed and discussed.

Tannic acid modified PdAu alloy nanowires as efficient oxygen reduction electrocatalysts

Design of the structure, composition and interface of the catalysts is very important to improve oxygen reduction reaction (ORR) catalytic activity under alkaline environment. Herein, we propose a direct method to rapid synthesis of tannic acid (TA) modified PdAu alloy nanowires (PdAu@TA NWs). Compared with pure PdAu NWs and commercial Pt/C, the PdAu@TA NWs exhibit superior ORR electrocatalytic activity (mass activity: 0.73 A mg^-1_metaland specific activity: 3.50 mA cm^-2), stability, and methanol tolerance in an alkaline medium because PdAu@TA NWs possess sufficient active sites and synergistic effect that can effectively promote the oxygen reduction, inhibit the oxidation of the catalyst and improve the methanol tolerance of the catalyst. This synthetic method is a promising strategy to prepare metallic catalyst with surface functionalization.

Extraordinary p-d Hybridization Interaction in Heterostructural Pd-PdSe Nanosheets Boosts C-C Bond Cleavage of Ethylene Glycol Electrooxidation

Advanced electrocatalysts for complete oxidation of ethylene glycol (EG) in direct EG fuel cells are strongly desired owing to the higher energy efficiency. Herein, Pd-PdSe heterostructural nanosheets (Pd-PdSe HNSs) have been successfully fabricated via a one-step approach. These Pd-PdSe HNSs feature unique electronic and geometrical structures, in which unconventional p-d hybridization interactions and tensile strain effect co-exist. Compared with commercial Pd/C and Pd NSs catalysts, Pd-PdSe HNSs display 5.5 (6.6) and 2.5 (2.6) fold enhancement of specific (mass) activity for the EG oxidation reaction (EGOR). Especially, the optimum C1 pathway selectivity of Pd-PdSe HNSs reaches 44.3 %, illustrating the superior C-C bond cleavage ability. Electrochemical in situ FTIR spectroscopy and theoretical calculations demonstrate that the extraordinary p-d hybridization interaction and tensile strain effect could effectively reduce the activation energy of C-C bond breaking and accelerate CO* oxidation, boosting the complete oxidation of EG and improving the catalytic performance.

Electronic and Potential Synergistic Effects of Surface-Doped P-O Species on Uniform Pd Nanospheres: Breaking the Linear Scaling Relationship toward Electrochemical Oxygen Reduction

Developing efficient oxygen reduction reaction (ORR) electrocatalysts is critical to fuel cells and metal-oxygen batteries, but also greatly hindered by the limited Pt resources and the long-standing linear scaling relationship (LSR). In this study, ∼6 nm and highly uniform Pd nanospheres (NSs) having surface-doped (SD) P-O species are synthesized and evenly anchored onto carbon blacks, which are further simply heat-treated (HT). Under alkaline conditions, Pd/^SDP-O NSs/C-HT exhibits respective 8.7 (4.3)- and 5.0 (5.5)-fold enhancements in noble-metal-mass- and area-specific activity (NM-MSA and ASA) compared with the commercial Pd/C (Pt/C). It also possesses an improved electrochemical stability. Besides, its acidic ASA and NM-MSA are 2.9 and 5.1 times those of the commercial Pd/C, respectively, and reach 65.4 and 51.5% of those of the commercial Pt/C. Moreover, it also shows nearly ideal 4-electron ORR pathways under both alkaline and acidic conditions. The detailed experimental and theoretical analyses reveal the following: (1) The electronic effect induced by the P-O species can downshift the surface d-band center to weaken the intermediate adsorptions, thus preserving more surface active sites. (2) More importantly, the potential hydrogen bond between the O atom in the P-O species and the H atom in the hydrogen-containing intermediates can in turn stabilize their adsorptions, thus breaking the ORR LSR toward more efficient ORRs and 4-electron pathways. This study develops a low-cost and high-performance ORR electrocatalyst and proposes a promising strategy for breaking the ORR LSR, which may be further applied in other electrocatalysis.

Cr-Doped Pd Metallene Endows a Practical Formaldehyde Sensor New Limit and High Selectivity

Electrochemical sensors for detecting micromolecule organics are desirable for improving the perception of environmental quality and human health. However, currently, the electrochemical sensors for formaldehyde are substantially limited on the market due to the long-term unsolved problems of the low electrooxidation efficiency and CO poisoning issue of commercial Pd catalysts. Here, a 2D Cr-doped Pd metallene (Cr-Pdene) with few atomic layers is shown as an advanced catalyst for ultrasensitive and selective sensing of formaldehyde via a highly efficient formaldehyde electrooxidation. It is found that the doping of Cr into Pd metallene can efficiently optimize the electronic structure of Pd and weaken the interaction between Pd and CO, providing an anti-poisoning means to favor CO₂ production and suppress CO adsorption. The Cr-Pdene-based electrochemical sensor exhibits one order of magnitude higher detection range and, especially, much higher anti-interference for formaldehyde than that of the conventional sensors. Most importantly, it is demonstrated that the Cr-Pdene can be integrated into commercializable wireless sensor networks or handheld instruments for promising applications relating to the environment, health, and food.

A ternary PdNiMo alloy as a bifunctional nanocatalyst for the oxygen reduction reaction and hydrogen evolution reaction

Mo0.2Pd3Ni/NC shows superior electrochemical performances for both ORR and HER due to the charge redistribution among Ni, Pd, and Mo, tuning the electronic structure of Pd.

Noble Metal (Pt, Rh, Pd, Ir) Doped Ru/CNT Ultra-Small Alloy for Acidic Hydrogen Evolution at High Current Density

There are still great challenges to prepare high-efficiency Ru-based catalysts that are superior to Pt/C under acidic conditions, especially under high current conditions. In this work, a series of surfactant-free noble metal doped Ru/CNT (M-Ru/CNT, M = Pt, Rh, Pd, Ir, CNT stands for carbon nanotube) are prepared by microwave reduction method in 1 minute with ≈3-3.5 nm in size for the first time. In 0.5 m H₂ SO₄ , the overpotential of Pt-Ru/CNT (Pt: 4.94 at %) is only 12 mV. What's more, it also has much larger electrochemical surface area and intrinsic activity than Pt/C. Pt-Ru/CNT still has an ultra-small overpotential under high current density (113 mV at 500 mA cm^-2 , 155 mV at 1000 mA cm^-2 ). At the same time, it possesses excellent stability regardless of high current or low current after the durability test of 100 h. Theoretical calculation also deeply reveals that Ru is the main adsorption site of H⁺ . The comparison of the electronic structure of a series of noble metals adjusted by Ru shows that Pt has the most excellent Gibbs free energy of the adsorbed hydrogen and promotes the desorption of the product.

Ultrathin PdAuBiTe Nanosheets as High-Performance Oxygen Reduction Catalysts for a Direct Methanol Fuel Cell Device

Ultrathin 2D metal nanostructures have sparked a lot of research interest because of their improved electrocatalytic properties for fuel cells. So far, no effective technique for preparing ultrathin 2D Pd-based metal nanostructures with more than three compositions has been published. Herein, a new visible-light-induced template technique for producing PdAuBiTe alloyed 2D ultrathin nanosheets is developed. The mass activity of the PdAuBiTe nanosheets against the oxygen reduction reaction (ORR) is 2.48 A mg_Pd ^-1 , which is 27.5/17.7 times that of industrial Pd/C/Pt/C, respectively. After 10 000 potential cyclings, there is no decrease in ORR activity. The PdAuBiTe nanosheets exhibit high methanol tolerance and in situ anti-CO poisoning properties. The PdAuBiTe nanosheets, as cathode electrocatalysts in direct methanol fuel cells, can thus give significant improvement in terms of power density and durability. In O₂ /air, the power density can be increased to 235.7/173.5 mW cm^-2 , higher than that reported in previous work, and which is 2.32/3.59 times higher than Pt/C.

Anion Modulation of Pt-Group Metals and Electrocatalysis Applications

Pt-group metal (PGM) electrocatalysts with unique electronic structures and irreplaceable comprehensive properties play crucial roles in electrocatalysis. Anion engineering can create a series of PGM compounds (such as RuP₂ , IrP₂ , PtP₂ , RuB₂ , Ru₂ B₃ , RuS₂ , etc.) that provide a promising prospect for improving the electrocatalytic performance and use of Pt-group noble metals. This review seeks the electrochemical activity origin of anion-modulated PGM compounds, and systematically analyzes and summarizes their synthetic strategies and energy-relevant applications in electrocatalysis. Orientation towards the sustainable development of nonfossil resources has stimulated a blossoming interest in the design of advanced electrocatalysts for clean energy conversion. The anion-modulated strategy for Pt-group metals (PGMs) by means of anion engineering possesses high flexibility to regulate the electronic structure, providing a promising prospect for constructing electrocatalysts with superior activity and stability to satisfy a future green electrochemical energy conversion system. Based on the previous work of our group and others, this review summarizes the up-to-date progress on anion-modulated PGM compounds (such as RuP₂ , IrP₂ , PtP₂ , RuB₂ , Ru₂ B₃ , RuS₂ , etc.) in energy-related electrocatalysis from the origin of their activity and synthetic strategies to electrochemical applications including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), N₂ reduction reaction (NRR), and CO₂ reduction reaction (CO₂ RR). At the end, the key problems, countermeasures and future development orientations of anion-modulated PGM compounds toward electrocatalytic applications are proposed.

Single Mn Atom Anchored on Nitrogen-Doped Graphene as a Highly Efficient Electrocatalyst for Oxygen Reduction Reaction

Single Mn atom on nitrogen-doped graphene (MnN₄ -G) has exhibited good structural stability and high activity for the adsorption and dissociation of an O₂ molecule, becoming a promising single-atom catalyst (SAC) candidate for oxygen reduction reaction (ORR). However, the catalytic activity of MnN₄ -G for the ORR and the optimal reaction pathway remain obscure. In this work, density-functional theory calculations were employed to comprehensively investigate all the possible pathways and intermediate reactions of the ORR on MnN₄ -G. The feasible active sites and the most stable adsorption configurations of the intermediates and transition states during the ORR were identified. Screened from all the possibilities, three optimal four-electron O₂ hydrogenation pathways with an ultralow energy barrier of 0.13 eV were discovered that are energetically more favorable than direct O₂ dissociation pathways. Analysis of the free energy diagram further verified the thermodynamical feasibility of the three pathways. Thus, MnN₄ -G possesses superior ORR activity. This study provides a fundamental understanding of the design of highly efficient SACs for the ORR.

Lattice-strain and electron-density modulation of palladium nanocatalysts for highly efficient oxygen reduction

Designing efficient electrocatalysts for the oxygen reduction reaction (ORR) is crucial to enhance the energy efficiencies of metal-air batteries and fuel cells. Palladium (Pd) catalysts show great potential due to their high intrinsic activity towards ORR but suffer from inferior durability. Here, we aim to employ tin oxide (SnO₂) supports to tailor the lattice strain and electron density of Pd catalysts to enhance their ORR performance. By using electrospinning and solvothermal techniques, a hierarchical Pd/SnO₂ hybrid catalyst was facilely synthesized with Pd nanoparticles anchored onto both the inside and outside walls of nanotube-like SnO₂ supports. Owing to the SnO₂ supports and the endowing metal-support interactions, tensile-strain and electron-rich features were both verified for the Pd nanoparticles in the Pd/SnO₂ catalyst. In comparison, no such features were found for the Pd nanoparticles in the Pd/C catalyst. As a consequence, the Pd/SnO₂ hybrid catalyst exhibits 2.5-times higher mass activity than the Pd/C catalyst and greatly improved durability with a current decay of 4% loss over 50 h compared with that (18%) of the Pd/C catalyst.

Amplified Interfacial Effect in an Atomically Dispersed RuOx -on-Pd 2D Inverse Nanocatalyst for High-Performance Oxygen Reduction

Atomically dispersed oxide-on-metal inverse nanocatalysts provide a blueprint to amplify the strong oxide-metal interactions for heterocatalysis but remain a grand challenge in fabrication. Here we report a 2D inverse nanocatalyst, RuO_x -on-Pd nanosheets, by in situ creating atomically dispersed RuO_x /Pd interfaces densely on ultrathin Pd nanosheets via a one-pot synthesis. The product displays unexpected performance toward the oxygen reduction reaction (ORR) in alkaline medium, which represents 8.0- and 22.4-fold enhancement in mass activity compared to the state-of-the-art Pt/C and Pd/C catalysts, respectively, showcasing an excellent Pt-alternative cathode electrocatalyst for fuel cells and metal-air batteries. Density functional theory calculations validate that the RuO_x /Pd interface can accumulate partial charge from the 2D Pd host and subtly change the adsorption configuration of O₂ to facilitate the O-O bond cleavage. Meanwhile, the d-band center of Pd nanosubstrates is effectively downshifted, realizing weakened oxygen binding strength.

High-Index Faceted PdPtCu Ultrathin Nanorings Enable Highly Active and Stable Oxygen Reduction Electrocatalysis

Ultrathin nanosheet catalysts deliver great potential in catalyzing the oxygen reduction reaction (ORR), but encounter the ceiling of the surface atomic utilizations, thus presenting a challenge associated with further boosting catalytic activity. Herein, a kind of PdPtCu ultrathin nanorings with increased numbers of electrocatalytically active sites is reported, with the purpose of breaking the activity ceiling of conventional catalysts. The as-made PdPtCu nanorings possess abundant high-index facets at the edge of both the exterior and interior surfaces. An ultrahigh electrochemical active surface area of 92.2 m² g^-1 _PGM is achieved on this novel catalyst, much higher than that of the commercial Pt/C catalyst. The optimized Pd₃₉ Pt₃₃ Cu₂₈ /C shows a great enhanced ORR activity with a specific activity of 2.39 mA cm^-2 and a mass activity of 1.97 A mg^-1 _PGM at 0.9 V (versus RHE), as well as superior durability within 30 000 cycles. Density function theory calculations reveal that the high-index facets and alloying Cu atoms can optimize the oxygen adsorption energy, explaining the enhanced ORR activity. Overcoming a key technical barrier in sub-nanometer electrocatalysts, this work successfully introduces the hollow structures into the ultrathin nanosheets, heralding the exciting prospects of high-performance ORR catalysts in fuel cells.

NixCu1−x/CuO/Ni(OH)2 as highly active and stable electrocatalysts for oxygen evolution reaction

Ni–Cu alloy-based nanomaterials are representative cost-effective materials that have been widely used as highly active and stable electrocatalysts for electrochemical energy applications, such as the water oxidation reaction, the methanol/ethanol reaction and many other small molecule oxidation reactions.

Ultrasmall PdPtCo trimetallic nanorings with enriched low-coordinated edge sites and optimized compositions for effective oxygen reduction electrocatalysis

Ultrasmall two-dimensional Pd₅₅Pt₁₈Co₂₇ trimetallic alloy nanorings with enriched low-coordinated edge sites exhibit greatly enhanced ORR electrocatalytic activity.

Dual roles of underpotential deposition in the synthesis of tetrahexahedral Pd–Ag alloy nanocrystals

Underpotential deposition of Ag(i) not only selectively passivates the high-index facets of tetrahexahedral nanocrystals, but also leads to the formation of Pd–Ag alloy structures.