Rational Design and Facile Preparation of Palladium-Based Electrocatalysts for Small Molecules Oxidation

Direct liquid fuel cells (DLFCs) can convert the chemical energy of small organic molecules directly into electrical energy, which is a promising technique and always calls for electrocatalysts with high activity, stability and selectivity. Palladium (Pd)-based catalysts for DLFCs have been widely studied with the pursuit of ultra-high performance, however, most of the preparation routes require complex agents, multi-operation steps, even extreme experimental conditions, which are high-cost, energy-consuming, and not conducive to the scalable and sustainable production of catalysts. In this review, the recent progresses on not only the rational design strategies, but also the facile preparation methods of Pd-based electrocatalysts for small molecules oxidation reaction (SMOR) are comprehensively summarized. Based on the principles of green chemistry in material synthesis, the basic rules of "facile method" have been restricted, and the fabrication processes, perks and drawbacks, as well as practical applications of the "real" facile methods have been highlighted. The landscape of this review is to facilitate the mild preparation of efficient Pd-based electrocatalysts for SMOR, that is, to achieve a balance between "facile preparation" and "outstanding performance", thereby to stimulate the huge potential of sustainable nano-electrocatalysts in various research and industrial fields.

Functional surfactant-directing ultrathin metallic nanoarchitectures as high-performance electrocatalysts

Ultrathin nanosheets possess a distinctive structure characterized by an abundance of active sites fully accessible on their surface. Concurrently, their nanoscale thickness confers an extraordinarily high specific surface area and promising electronic properties. To date, numerous strategies have been devised for synthesizing precious metal nanosheets that exhibit excellent electrocatalytic performance. In this paper, recent progress in the controlled synthesis of two-dimensional, ultrathin nanosheets by a self-assembly mechanism using functional surfactants is reviewed. The aim is to highlight the key role of functional surfactants in the assembly and synthesis of two-dimensional ultrathin nanosheets, as well as to discuss in depth how to enhance their electrochemical properties, thereby expanding their potential applications in catalysis. We provide a detailed exploration of the mechanisms employed by several long-carbon chain surfactants commonly used in the synthesis of nanosheets. These surfactants exhibit robust electrostatic and hydrophobic effects, effectively confining the crystalline growth of metals along lamellar micelles. Moreover, we present an overview of the electrocatalytic performance demonstrated by the ultrathin nanosheets synthesized through this innovative pathway. Furthermore, it offers valuable insights that may pave the way for further exploration of more functional long-chain surfactants, leading to the synthesis of ultrathin nanosheets with significantly enhanced electrocatalytic performance.

Lattice engineering of noble metal-based nanomaterials via metal-nonmetal interactions for catalytic applications

Noble metal-based nanomaterials possess outstanding catalytic properties in various chemical reactions. However, the increasing cost of noble metals severely hinders their large-scale applications. A cost-effective strategy is incorporating noble metals with light nonmetal elements (e.g., H, B, C, N, P and S) to form noble metal-based nanocompounds, which can not only reduce the noble metal content, but also promote their catalytic performances by tuning their crystal lattices and introducing additional active sites. In this review, we present a concise overview of the recent advancements in the preparation and application of various kinds of noble metal-light nonmetal binary nanocompounds. Besides introducing synthetic strategies, we focus on the effects of introducing light nonmetal elements on the lattice structures of noble metals and highlight notable progress in the lattice strain engineering of representative core-shell nanostructures derived from these nanocompounds. In the meantime, the catalytic applications of the light element-incorporated noble metal-based nanomaterials are discussed. Finally, we discuss current challenges and future perspectives in the development of noble metal-nonmetal based nanomaterials.

A defect-enriched PdMo bimetallene for ethanol oxidation reaction and 4-nitrophenol reduction

A defect-enriched PdMo bimetallene (d-PdMo) was prepared by a one-pot wet chemical reaction followed by post-treatment of oxidative etching. The introduction of defects can tailor the electronic structure of PdMo bimetallene and the prepared d-PdMo bimetallene exhibited excellent performance in the ethanol oxidation reaction (EOR) and 4-nitrophenol (4-NP) reduction reaction.

Ultrathin PdPtP nanodendrites as high-activity electrocatalysts toward alcohol oxidation

PdPtP nanodendrites were prepared by a post-phosphating method. Due to their well-designed structure and composition, the EOR activity of the PtPdP NDs is significantly increased to 14.3 A mgPd+Pt-1, which is a significant improvement compared to commercial Pd/C catalysts. In addition, stability tests demonstrated their excellent catalytic activity and structural durability.

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.

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.

Pd-Sb Rhombohedra with an Unconventional Rhombohedral Phase as a Trifunctional Electrocatalyst

Crystal phase engineering is an important strategy for designing noble-metal-based catalysts with optimized activity and stability. From the thermodynamic point of view, it remains a great challenge to synthesize unconventional phases of noble metals. Here, a new class of Pd-based nanostructure with unconventional rhombohedral Pd₂₀ Sb₇ phase is successfully synthesized. Benefiting from the high proportion of the unique exposed Pd₂₀ Sb₇ (003) surface, Pd₂₀ Sb₇ rhombohedra display much enhanced ethanol oxidation reaction (EOR) and oxygen reduction reaction performance compared with commercial Pd/C. Moreover, Pd₂₀ Sb₇ rhombohedra are also demonstrated as an effective air cathode in non-aqueous Li-air batteries with an overpotential of only 0.24 V. Density functional theory calculations reveal that the unique exposed facets of Pd₂₀ Sb₇ rhombohedra can not only reduce the excessive adsorption of CH₃ CO* to CH₃ COOH on Pd for promoting EOR process, but also weaken CO binding and CO poisoning. This work provides a new class of unconventional intermetallic nanomaterials with enhanced electrocatalytic activity.

Ethanol-Induced Hydrogen Insertion in Ultrafine IrPdH Boosts pH-Universal Hydrogen Evolution

Engineering Pt-free catalysts for hydrogen evolution reaction (HER) with high activity and stability is of great significance in electrochemical hydrogen production. Herein, in situ chemical H intercalation into ultrafine Pd to activate this otherwise HER-inferior material to form the ultrafine IrPdH hydride as an efficient and stable HER electrocatalyst is proposed. The formation of PdIrH depends on a new hydrogenation strategy via using ethanol as the hydrogen resource. It is demonstrated that H atoms in IrPdH originate from the OH and CH₂  of ethanol, which fills the gap of ethanol as the hydrogen source for the preparation of Pd hydride. Thanks to the incorporation of H/Ir atoms and ultrafine structure, the IrPdH exhibits superior HER activity and stability in the whole pH range. The IrPdH delivers very low overpotentials of 14, 25 and 60 mV at a current density of 10 mA cm^-2 respectively in 0.5 m H₂ SO₄ , 1 m KOH, and 1 m PBS electrolytes, which are much better than those of commercial Pt/C and most reported noble metal electrocatalysts. Theoretical calculations confirm that interstitial hydrogen availably refines the electronic density of Pd and Ir sites, which optimizes the adsorption of *H and leads to the significant enhancement of HER performance.

Ternary PdCoP nanoparticles with nanopore structures: synergic boosting of electrocatalytic activity for ethanol oxidation

PdCoP nanoparticles (PdCoP NPs) with nanopore structures were synthesized by a facile one-pot solvothermal approach. Due to their unique geometric structures and the electronic and synergistic effects among multiple components, the optimized PdCoP NPs (PdCoP-NPs-1) show superior mass activity (5.97 A mg_Pd^-1) for the ethanol oxidation reaction under alkaline conditions.

Amorphous-crystalline PdRu bimetallene for efficient hydrogen evolution electrocatalysis

In this work, PdRu bimetallene is prepared by a wet-chemical method using CO as a structure-directing agent and reductant derived from the decomposition of W(CO)₆. The PdRu bimetallene exhibits excellent catalytic activity with a small overpotential of -32 mV compared to Pd metallene (-62 mV) at -10 mA cm^-2 in acidic conditions.

Low Pt-Doped Crystalline/Amorphous Heterophase Pd12P3.2 Nanowires as Efficient Catalysts for Methanol Oxidation

Pd-based catalysts are attractive anodic electrocatalysts for direct methanol fuel cells owing to their low cost and natural abundance. However, they suffer from sluggish reaction kinetic and insufficient electroactivity in methanol oxidation reaction (MOR). In this work, we developed a facile one-pot approach to fabricate low Pt-doped Pd₁₂P_3.2 nanowires with crystalline/amorphous heterophase (termed Pt-Pd₁₂P_3.2 NWs) for MOR. The unique crystalline/amorphous heterophase structures promote the catalytic activity by the plentiful active sites at the phase boundaries and/or interfaces and the synergistic effect between different phases. Moreover, the incorporation of trace Pt into Pd lattices modifies the electronic structure and improves the electron transfer ability. Therefore, the obtained Pt-Pd₁₂P_3.2 NWs display significantly enhanced electrocatalytic performance toward MOR with the mass activity of 2.35 A mg_Pd+Pt^-1, which is 9.0, 2.9, and 2.0 times higher than those of the commercial Pd/C (0.26 A mg_Pd^-1), Pd₁₂P_3.2 NWs (0.82 A mg_Pd^-1), and commercial Pt/C (1.19 A mg_Pt^-1). The high mass activity enables the Pt-Pd₁₂P_3.2 NWs to be the promising Pd-based catalysts for MOR.

Ultrathin RhCuAgPd/Pd nanowire heterostructures for ethylene glycol electrooxidation

Ultrathin RhCuAgPd/Pd nanowire heterostructures were prepared by a seed-mediated growth method. Due to the synergistic structural (including ultrathin NWs and interfaces) and compositional (Pd, Rh, Cu and Ag) advantages, the RhCuAgPd/Pd NWs exhibit superior electrocatalytic performance toward ethylene glycol oxidation under alkaline conditions, including high mass activity (6.63 A mg_Pd^-1), fine stability/durability and resistance to CO poisoning, favourable electrocatalytic kinetics and low activation energy values (18.64 kJ mol^-1).

Nickel chalcogenides as selective ethanol oxidation electro-catalysts and their structure-performance relationships

Five nickel chalcogenides have been studied and they showed high selectivity towards selective ethanol electro-oxidation to acetic acid. The activities of the different nickel chalcogenides are correlated with the Ni-Ni projected distances of the catalysts.

Kinetics-Controlled Synthesis of Gold-Silver Nanosheets with Abundant in-Plane Cracking and Their Trimetallic Derivatives for Plasmon-Enhanced Catalysis

Controlled synthesis of two-dimensional noble metal nanomaterials with in-plane branching morphology has been of great research interest recently, which yet achieves limited success for AuAg-based nanocrystals. Herein, we report the...

Amorphous Palladium-Based Alloy Nanoparticles as Highly Active Electrocatalysts for Ethanol Oxidation

Amorphous Pd-P metal-metalloid alloy nanoparticles showed higher electrochemical ethanol oxidation reaction performance than the crystalline Pd nanopartilces. The high performance was attributed to the rich defective coordination unsaturated sites and...

Rapid Aqueous Synthesis of Large-Size and Edge/Defect-Rich Porous Pd and Pd-Alloyed Nanomesh for Electrocatalytic Ethanol Oxidation

In this work, a facile aqueous synthesis strategy was used (complete in 5 min at room temperature) to produce large-size Pd, PdCu, and PdPtCu nanomeshes without additional organic ligands or solvent and the volume restriction of reaction solution. The obtained metallic nanomeshes possess graphene-like morphology and a large size of dozens of microns. Abundant edges (coordinatively unsaturated sites, steps, and corners), defects (twins), and mesopores are seen in the metallic ultrathin structures. The formation mechanism for porous Pd nanomeshes disclosed that they undergo oriented attachment growth along the ⟨111⟩ direction. Owing to structural and compositional advantages, PdCu porous nanomeshes with certain elemental ratios (e. g., Pd₈₇ Cu₁₃ ) presented enhanced electrocatalytic performance (larger mass activity, better CO tolerance and stability) toward ethanol oxidation.

Ultrathin and Wavy PdB Alloy Nanowires with Controlled Surface Defects for Enhanced Ethanol Oxidation Electrocatalysis

Engineering crystalline structures/defects and elemental compositions is synthetically critical to optimize surface features of noble metal nanocrystals and thus improve their catalytic performances in various reactions. In this manuscript, we report a facile one-step aqueous synthesis of one-dimensional (1D) noble metal-metalloid alloy nanowires (NWs) with an ultrathin and wavy morphology, controlled crystalline defects, and binary PdB compositions as a highly efficient catalyst toward the electrochemical ethanol oxidation reaction (EOR). We show that the utilization of hexadecylpyridinium chloride as functional surfactant is of great importance to confine in-the-columnar epitaxial nucleation of anisotropic ultrathin PdB NWs, while the attachment growth precisely controls their surface crystalline defects with a wavy morphology. Meanwhile, this strategy is synthetically universal and can be readily extended to engineer an ultrathin wavy morphology and crystalline defect of ternary PdMB (M = Cu and Pt) alloy NWs. Owing to multiple structural and compositional merits, resultant PdB alloy NWs synergistically expose more electrocatalytically active sites and also kinetically accelerate the removal of CO-related poisons, remarkably improving electrocatalytic EOR activity and stability compared to their counterpart catalysts. Besides, wavy PdB alloy NWs are also electrochemically more active for electrocatalytic oxidation of other alcohols (methanol, glycerol, and glucose). The findings reported here thus shed a bright light on rational design of the high-performance metal alloy catalysts for their potential applications in fine chemical synthesis, fuel cells, and beyond.