Ternary Palladium-Boron-Phosphorus Alloy Mesoporous Nanospheres for Highly Efficient Electrocatalysis

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.

One-Pot Synthesis of Pd Nanoparticles Supported on Carbide-Derived Carbon for Oxygen Reduction Reaction

We explored two methods for synthesizing Pd nanoparticles using three different carbide-derived carbon (CDC) support materials, one of which was nitrogen-doped. These materials were studied for oxygen reduction reaction (ORR) in 0.1 M KOH solution, and the resulting CDC/Pd catalysts were characterized using TEM, XRD, and XPS. The citrate method and the polyol method using polyvinylpyrrolidone (PVP) as a capping agent were employed to elucidate the impact of the support material on the final catalyst. The N-doping of the CDC material resulted in smaller Pd nanoparticles, but only in the case of the citrate method. This suggests that the influence of support is weaker when using the polyol method. The citrate method with CDC1, which is predominantly microporous, led to a higher degree of agglomeration and formation of larger particles in comparison to supports, which possessed a higher degree of mesoporosity. We achieved smaller Pd particle sizes using citrate and NaBH4 compared to the ethylene glycol PVP method. Pd deposited on CDC2 and CDC3 supports showed similar specific activity (SA), suggesting that the N-doping did not significantly influence the ORR process. The highest SA value was observed for CDC1/Pd_Cit, which could be attributed to the formation of larger Pd particles and agglomerates.

Crystalline-Amorphous Heterophase PdMoCrW Tetrametallene: Highly Efficient Oxygen Reduction Electrocatalysts for a Long-Term Zn-Air Battery

Metallenes have received sustained attention owing to their unique microstructure characteristics and compelling catalytic applications, but the synthesis of multielement crystalline-amorphous metallenes remains a formidable challenge. Herein, we report a one-step wet chemical reduction method to synthesize composition-tunable crystalline-amorphous heterophase PdMoCrW tetrametallene. As-synthesized PdMoCrW tetrametallene is composed of approximately six to seven atomic layers and has flexible crimpiness, a crystalline-amorphous heterophase structure, and high-valence metal species. Time-dependent experiments show that PdMoCrW tetrametallene follows a three-step growth mechanism that includes nucleation, lateral growth, and atom diffusion, respectively. The novel ultrathin structure, optimized Pd electronic structure, and hydrophilic surface together greatly promote the activity and stability of PdMoCrW tetrametallene in the alkaline oxygen reduction reaction. Pd75.9Mo9.4Cr8.9W5.8/C exhibits excellent mass and specific activities of 2.81 A mgPd-1 and 4.05 mA cm-2, which are 20.07/14.46 and 23.42/16.20 times higher than those of commercial Pt/C and Pd/C, respectively. Furthermore, a Zn-air battery assembled using Pd75.9Mo9.4Cr8.9W5.8/C as a cathode catalyst achieves a peak power density of 156 mW cm-2 and an ultralong durability of 329 h. This study reports an effective strategy for constructing crystalline-amorphous quaternary metallenes to advance non-Pt electrocatalysts toward oxygen reduction reaction (ORR) performance and for a Zn-air battery.

Ordered Mesoporous Crystalline Frameworks Toward Promising Energy Applications

Ordered mesoporous crystalline frameworks (MCFs), which possess both functional frameworks and well-defined porosity, receive considerable attention because of their unique properties including high surface areas, large pore sizes, tailored porous structures, and compositions. Construction of novel crystalline mesoporous architectures that allows for rich accessible active sites and efficient mass transfer is envisaged to offer ample opportunities for potential energy-related applications. In this review, the rational synthesis, unique structures, and energy applications of MCFs are the main focus. After summarizing the synthetic approaches, an emphasis is placed on the delicate control of crystallites, mesophases, and nano-architectures by concluding basic principles and showing representative examples. Afterward, the currently fabricated components of MCFs such as metals, metal oxides, metal sulfides, and metal-organic frameworks are described in sequence. Further, typical applications of MCFs in rechargeable batteries, supercapacitors, electrocatalysis, and photocatalysis are highlighted. This review ends with the possible development and synthetic challenges of MCFs as well as a future prospect for high-efficiency energy applications, which underscores a pathway for developing advanced materials.

Two-dimensional mesoporous metals: a new era for designing functional electrocatalysts

Two-dimensional (2D) mesoporous metals contribute a unique class of electrocatalyst materials for electrochemical applications. The penetrated mesopores of 2D mesoporous metals expose abundant accessible undercoordinated metal sites, while their 2D nanostructures accelerate the transport of electrons and reactants. Therefore, 2D mesoporous metals have exhibited add-in structural functions with great potential in electrocatalysis that not only enhance electrocatalytic activity and stability but also optimize electrocatalytic selectivity. In this Perspective, we summarize recent progress in the design, synthesis, and electrocatalytic performance of 2D mesoporous metals. Four main strategies for synthesizing 2D mesoporous metals, named the CO (and CO container) induced route, halide ion-oriented route, interfacial growth route, and metal oxide atomic reconstruction route, are presented in detail. Moreover, electrocatalytic applications in several important reactions are summarized to highlight the add-in structural functions of 2D mesoporous metals in enhancing electrochemical activity, stability, and selectivity. Finally, current challenges and future directions are discussed in this area. This Perspective offers some important insights into both fundamental investigations and practical applications of novel high-performance functional electrocatalysts.

High entropy alloying strategy for accomplishing quintuple-nanoparticles grafted carbon towards exceptional high-performance overall seawater splitting

High entropy alloys (HEAs), a novel class of material, have been explored in terms of their excellent mechanical properties. Seawater electrolysis is a step towards sustainable production of carbon-neutral fuels such as H2, O2, and industrially demanding Cl2. Herein, we report a practically viable FeCoNiMnCr HEA nanoparticles system grafted on a conductive carbon matrix for promising seawater electrolysis. The comprehensive kinetics analysis of the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and chlorine evolution reaction (CER) confirms the effectiveness of our system. As an electrocatalyst, HEAs grafted on carbon black show trifunctionality with promising kinetics, selectivity and enduring performance, towards seawater splitting. We optimize high entropy alloy decorated/grafted carbon black (HEACB) catalysts, studying their synthesis temperature to scrutinize the effect of alloy formation variation on the catalysis efficacy. During the catalysis, selectivity between two mutually competing reactions, CER and OER, in the electrochemical catalysis of seawater is controlled by the reaction media pH. We employ Mott-Schottky measurements to probe the band structure of the intrinsically induced metal-semiconductor junction in the HEACB catalyst, where the carrier density and flat band potential are optimized. The HEACB sample provides promising results towards overall seawater electrolysis with a net half-cell potential of about 1.65 V with good stability, which strongly implies its broad practical applicability.

A general protocol for precise syntheses of ordered mesoporous intermetallic nanoparticles

Intermetallic nanomaterials consist of two or more metals in a highly ordered atomic arrangement. There are many possible combinations and morphologies, and exploring their properties is an important research area. Their strict stoichiometry requirement and well-defined atom binding environment make intermetallic compounds an ideal research platform to rationally optimize catalytic performance. Making mesoporous intermetallic materials is a further advance; crystalline mesoporosity can expose more active sites, facilitate the mass and electron transfer, and provide the distinguished mesoporous nanoconfinement environment. In this Protocol, we describe how to prepare ordered mesoporous intermetallic nanomaterials with controlled compositions, morphologies/structures and phases by a general concurrent template strategy. In this approach, the concurrent template used is a hybrid of mesoporous platinum or palladium and Korea Advanced Institute of Science and Technology-6 (KIT-6) (meso-Pt/KIT-6 or meso-Pd/KIT-6) that can be transformed by the second precursors under reducing conditions. The second precursor can either be a second metal or a metalloid/non-metal, e.g., boron/phosphorus. KIT-6 is a silica scaffold that is removed using NaOH or HF to form the mesoporous product. Procedures for example catalytic applications include the 3-nitrophenylacetylene semi-hydrogenation reaction, p-nitrophenol reduction reaction and electrochemical hydrogen evolution reaction. The synthetic strategy for preparation of ordered mesoporous intermetallic nanoparticles would take almost 5 d; the physical characterization by electron microscope, X-ray diffraction and inductively coupled plasma-mass spectrometry takes ~2 days and the function characterization depends on the research question, but for catalysis it takes 1-5 h.

B-Doping-Induced Lattice Expansion of Pd Metallene Nanoribbons for Oxygen Reduction Reaction

Pd-based metallene is regarded as an efficient catalyst in the field of oxygen reduction reaction (ORR) because of its fantastic physicochemical features. The morphological structure control, lattice strain engineering, and electronic structure modulation of Pd-based metallene are effective tactics to enhance its electrocatalytic performance. In this work, we fabricate atomically thin B-doped Pd metallene nanoribbons (B-Pd MNRs) for efficient alkaline ORR. The atomically thin nanoribbon structure of B-Pd MNRs can expose many surface atoms as catalytically active sites. Moreover, the incorporation of boron effectively induces the lattice expansion and modulates the electronic structure of Pd, which can synergistically weaken the adsorption of intermediate species on B-Pd MNRs. Therefore, the B-Pd MNRs display excellent activity and durability for ORR. This work opens an avenue to the synthesis of atomically thin heteroatom-doped metallene nanoribbons for energy electrocatalytic applications.

Abundant Exterior/Interior Active Sites Enable Three-Dimensional PdPtBiTe Dumbbells C-C Cleavage Electrocatalysts for Actual Alcohol Fuel Cells

Developing high-activity electrocatalysts is of great significance for the commercialization of direct alcohol fuel cells (DAFCs), but it still faces challenges. Herein, three-dimensional (3D) porous PdPtBiTe dumbbells (DBs) were successfully fabricated via the visible photoassisted method. The alloying effect, defect-rich surface/interface and nanoscale cavity, and open pores make the 3D PdPtBiTe DBs a comprehensive and remarkable electrocatalyst for the C1-C3 alcohol (ethanol, ethylene glycol, glycerol, and methanol) oxidation reaction (EOR, EGOR, GOR, and MOR, respectively) in an alkaline electrolyte, and the results of in situ Fourier transform infrared spectra revealed a superior C-C bond cleavage ability. The 3D PdPtBiTe DBs exhibit ultrahigh EOR, EGOR, GOR, and MOR mass activities of 25.4, 23.2, 16.8, and 18.3 A mgPd + Pt-1, respectively, considerably surpassing those of the commercial Pt/C and Pd/C. Moreover, the mass peak power densities of 3D PdPtBiTe DBs in actual ethanol, ethylene glycol, glycerol, or methanol fuel cells increase to 409.5, 501.5, 558.0, or 601.3 mW mgPd + Pt-1 in O2, respectively. This study provides a new class of multimetallic nanomaterials as state-of-the-art multifunctional anode electrocatalysts for actual DAFCs.

Synthesis and Evaluation of Alginate-Based Nanogels as Sustained Drug Carriers for Caffeine

The objective of this study is to design a polymeric network of nanogels for sustained release of caffeine. Therefore, alginate-based nanogels were fabricated by a free-radical polymerization technique for the sustained delivery of caffeine. Polymer alginate was crosslinked with monomer 2-acrylamido-2-methylpropanesulfonic acid by crosslinker N',N'-methylene bisacrylamide. The prepared nanogels were subjected to sol-gel fraction, polymer volume fraction, swelling, drug loading, and drug release studies. A high gel fraction was seen with the increasing feed ratio of polymer, monomer, and crosslinker. Greater swelling and drug release were observed at pH 4.6 and 7.4 as compared to pH 1.2 due to the deprotonation and protonation of functional groups of alginate and 2-acrylamido-2-methylpropanesulfonic acid. An increase was observed in swelling, loading, and release of the drug with the incorporation of a high feed ratio of polymer and monomer, while a reduction was seen with the increase in crosslinker feed ratio. Similarly, an HET-CAM test was used to evaluate the safety of the prepared nanogels, which showed that the prepared nanogels have no toxic effect on the chorioallantoic membrane of fertilized chicken eggs. Similarly, different characterizations techniques such as FTIR, DSC, SEM, and particle size analysis were carried out to determine the development, thermal stability, surface morphology, and particle size of the synthesized nanogels, respectively. Thus, we can conclude that the prepared nanogels can be used as a suitable agent for the sustained release of caffeine.

Sulfur and phosphorus co-doping optimized electronic structure and modulated intermediate affinity on PdSP metallene for ethanol-assisted energy-saving H2 production

Coupling cathodic hydrogen evolution reaction (HER) and anodic electrochemical oxidation of organic small molecules in a co-electrolysis system could simultaneously realize high-value chemical generation and energy-saving hydrogen production, which, however, require high-performance electrocatalysts. In this work, we developed a one-step solvothermal method to synthesize S, P-co-doped Pd metallene (PdSP metallene) and employed it as a bifunctional electrocatalyst for both the HER and ethanol oxidation reaction (EOR). The co-doping of S and P atoms into Pd metallene could introduce multiple active sites and increase the electrochemically-active surface area. Moreover, the electronic interactions between Pd, S, and P atoms could regulate the electronic structure of the active sites and modulate the intermediate affinity on the resultant PdSP metallene, thus boosting the electrocatalytic HER and EOR performance. In the HER-EOR co-electrolysis system with bifunctional PdSP metallene electrocatalysts, only a 0.88 V of electrolysis voltage was required to fulfill 10 mA cm^-2 current density, much lower than that of pure water electrolysis (1.41 V) using the same electrocatalysts.

Subnanoscale Dual-Site Pd-Pt Layers Make PdPtCu Nanocrystals CO-Tolerant Bipolar Effective Electrocatalysts for Alcohol Fuel Cell Devices

Finding a high-performance low-Pt bipolar electrocatalyst in actual direct alcohol fuel cells (DAFCs) remains challenging and desirable. Here, we developed a crystalline PdPtCu@amorphous subnanometer Pd-Pt "dual site" layer core-shell structure for the oxygen reduction reaction (ORR) and alcohol (methanol, ethylene glycol, glycerol, and their mixtures) oxidation reaction (AOR) in an alkaline electrolyte (denoted D-PdPtCu). The prepared D-PdPtCu/C achieved a direct 4-electron ORR pathway, a full oxidation pathway for AOR, and high CO tolerance. The ORR mass activity (MA) of D-PdPtCu/C delivered a 52.8- or 59.3-fold increase over commercial Pt/C or Pd/C, respectively, and no activity loss after 20000 cycles. The D-PdPtCu/C also exhibited much higher AOR MA and stability than Pt/C or Pd/C. Density functional theory revealed the intrinsic nature of a subnanometer Pd-Pt "dual site" surface for ORR and AOR activity enhancement. The D-PdPtCu/C as an effective bipolar electrocatalyst yielded higher peak power densities than commercial Pt/C in actual DAFCs.

Microporous PdCuB nanotag-based electrochemical aptasensor with Au@CuCl2 nanowires interface for ultrasensitive detection of PD-L1-positive exosomes in the serum of lung cancer patients

Programmed cell death ligand 1 protein-positive (PD-L1⁺) exosomes have been found to be a potential biomarker for the diagnosis of non-small cell lung cancer (NSCLC). However, the development of highly sensitive detection technique for PD-L1⁺ exosomes is still a challenge in clinical applications. Herein, a sandwich electrochemical aptasensor based on ternary metal-metalloid palladium-copper-boron alloy microporous nanospheres (PdCuB MNs) and Au@CuCl₂ nanowires (NWs) was designed for the detection of PD-L1⁺ exosomes. The excellent peroxidase-like catalytic activity of PdCuB MNs and the high conductivity of Au@CuCl₂ NWs endow the fabricated aptasensor with intense electrochemical signal, thus enabling the detection of low abundance exosomes. The analytical results revealed that the aptasensor maintained favorable linearity over a wide concentration range of 6 orders of magnitude and reached a low detection limit of 36 particles/mL. The aptasensor is successfully applied to the analysis of complex serum samples and achieves the accurate identification of clinical NSCLC patients. Overall, the developed electrochemical aptasensor provides a powerful tool for early diagnosis of NSCLC.

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.

Highly Selective Pd Nanosheet Aerogel Catalyst with Hybrid Strain Induced by Laser Irradiation and P Doping Postprocess

Strain engineering of electrocatalysts provides an effective strategy to improve the intrinsic catalytic activity. Here, the defect-rich crystalline/amorphous Pd nanosheet aerogel with hybrid microstrain and lattice strain is synthesized by combining laser irradiation and phosphorus doping methods. The surface strain exhibited by the microstrain and lattice strain shifts the d-band center of the electrocatalyst, enhancing the adsorption of intermediates in the ethanol oxidation reaction and thus improving the catalytic performances. The measured mass activity, specific activity and C1-path selectivity of the Pd nanosheet aerogel are 4.48, 3.06, and 5.06 times higher than those of commercial Pd/C, respectively. These findings afford a new strategy for the preparation of highl activity and C1 pathway selective catalysts and provide insight into the catalytic mechanism of strain-rich heterojunction materials based on tunable surface strain values.

Synthesis and Study of Palladium Mono- and Bimetallic (with Ag and Pt) Nanoparticles in Catalytic and Membrane Hydrogen Processes

A controlled strategy for the electrochemical synthesis of mono- and bimetallic nanoparticles with a unique and complex morphology has been developed. The investigation of the effect of changing the surfactant concentration and current density regulating the medium pH has revealed the fundamental patterns of nanoparticle growth. The developed method has allowed to synthesis of nanoparticles with a controlled pentabranched structure for the monometallic palladium as well as for favorable combinations of metals-Pd-Ag and Pd-Pt. The obtained nanoparticles were investigated in alkaline methanol oxidation. The results demonstrated quite high catalytic activity up to 83.51 mA cm^-2 and long-term stability, which are caused by the increase in electrochemically active surface area by increasing the active center's number. This was made possible due to the creation of unusual nanoparticle morphology, namely the presence of high-energy high-index facets. The developed nanoparticles were also studied as a modifying coating for hydrogen-permeable membranes in the processes of hydrogen transport. The membranes coated with the nanoparticles demonstrated sufficiently high hydrogen flux up to 11.33 mmol s^-1 m^-2 and high H₂/N₂ selectivity up to 2254. Such results can be explained by the obvious acceleration of surface processes through the application of the developed nanoparticles. The novel synthesis strategy can potentially be extended to other metal nanoparticle systems. Thus it can be an effective way to solve relevant problems of design of controlled synthetic methods allowing the nanoparticle morphology tuning according to the required functional properties.

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.

B, P-co-doped PdCu nanothorn assemblies for enhanced oxygen reduction electrolysis

Nonmetal doping is a promising strategy to improve electrocatalytic performance of noble metal based catalysts for oxygen reduction reaction (ORR). Herein, we report a facile method to fabricate PdCuBP nanothorn assemblies (PdCuBP NTAs) by co-doping B and P into pre-synthesized PdCu NTAs using NaBH₄and NaH₂PO₂as B source and P source, respectively. The metal-nonmetal structure and multi-branched morphology can optimize oxygen adsorption energy and avoid catalyst migration, agglomeration and Ostwald ripening. As such, the obtained PdCuBP NTAs exhibit efficient activity and excellent long-term stability for ORR. This research offers an excellent strategy for co-doping nonmetal elements into metal nanocrystals with controllable composition and structure to improve electrocatalytic ORR performance.

Highly efficient oxygen evolution reaction enabled by phosphorus-boron facilitating surface reconstruction of amorphous high-entropy materials

Efficient, cost-effective and durable electrocatalysts are highly required to overcome the slow kinetics and high overpotential of oxygen evolution reaction (OER). Here we report a series of novel amorphous high-entropy borophosphate catalysts FeCoNiMBPO_x (M = Mg, Al, Cr, Mn) prepared by a low-temperature reduction method. The leaching of boron and phosphorus accelerates the surface self-reconstruction of FeCoNiMnBPO_x, and the subsequently formed high-oxidation-state metal-OOH species is beneficial to improve the catalyst performance. Moreover, the unique amorphous structure with abundant defects provides more active sites for OER. As a return, all the samples exhibit excellent OER activity and stability. Among them, FeCoNiMnBPO_x with the highest conductivity and the largest electrochemical active surface area (ECSA) exhibits the best electrocatalytic performance, requiring only low overpotentials of 248 mV and 294 mV to reach current densities of 10 mA cm^-2 and 100 mA cm^-2, respectively. This sample also shows an exceptional durability for 50 h without a significant increase in potential, which is superior to that of the benchmark RuO₂ electrocatalyst. The combination of the adsorbate evolution mechanism (AEM) and the lattice oxygen-mediated mechanism (LOM) are responsible for the excellent catalyst performance. This work provides new ideas for designing high-activity multiple-element catalysts.

Noble-Metal-Based Hollow Mesoporous Nanoparticles: Synthesis Strategies and Applications

As second-generation mesoporous materials, mesoporous noble metals (NMs) are of significant interest for their wide applications in catalysis, sensing, bioimaging, and biotherapy owing to their structural and metallic features. The introduction of interior hollow cavity into NM-based mesoporous nanoparticles (MNs), which subtly integrate hierarchical hollow and mesoporous structure into one nanoparticle, produces a new type of hollow MNs (HMNs). Benefiting from their higher active surface, better electron/mass transfer, optimum electronic structure, and nanoconfinement space, NM-based HMNs exhibit their high efficiency in enhancing catalytic activity and stability and tuning catalytic selectivity. In this review, recent progress in the design, synthesis, and catalytic applications of NM-based HMNs is summarized, including the findings of the groups. Five main strategies for synthesizing NM-based HMNs, namely silica-assisted surfactant-templated nucleation, surfactant-templated sequential nucleation, soft "dual"-template, Kirkendall effect in synergistic template, and galvanic-replacement-assisted surfactant template, are described in detail. In addition, the applications in ethanol oxidation electrocatalysis and hydrogenation reactions are discussed to highlight the high activity, enhanced stability, and optimal selectivity of NM-based HMNs in (electro)catalysis. Finally, the further outlook that may lead the directions of synthesis and applications of NM-based HMNs is prospected.

Mesoporous Gold Nanostructures: Synthesis and Beyond

Mesoporous metal nanostructures have offered multiple advantages that cannot be realized elsewhere. These materials have been attracting more research attention in catalysis and electrocatalysis owing to their functional structures and compositions. Of the various mesoporous metals available, mesoporous gold (mesoAu) nanostructures are of special interest in surface-enhanced Raman scattering (SERS) and related applications because of their strong electromagnetic field (localized surface plasmon resonance). In the last few decades, various synthesis strategies have been developed to prepare mesoAu nanostructures with controllable morphologies that exhibit fascinating physicochemical properties and increase applications in SERS, catalysis, and electrocatalysis. In this Perspective, we systematically summarize recent advances in synthesis and applications of mesoAu nanostructures. Four synthesis strategies, including dealloying, nanocasting, electrochemical deposition, and intermediate template, are discussed in detail. Moreover, physicochemical properties and promising applications of mesoAu nanostructures are presented. Finally, we describe current challenges and give a general outlook to explore further directions in synthesis and applications of mesoAu nanostructures.

Recent advances in fuel cell reaction electrocatalysis based on porous noble metal nanocatalysts

As the center of fuel cells, electrocatalysts play a crucial role in determining the conversion efficiency from chemical energy to electrical energy. Therefore, the development of advanced electrocatalysts with both high activity and stability is significant but challenging. Active site, mass transport, and charge transfer are three central factors influencing the catalytic performance of electrocatalysts. Endowed with rich available surface active sites, facilitated electron transfer and mass diffusion channels, and highly active components, porous noble metal nanomaterials are widely considered as promising electrocatalysts toward fuel cell-related reactions. The past decade has witnessed great achievements in the design and fabrication of advanced porous noble metal nanocatalysts in the field of electrocatalytic fuel oxidation reaction (FOR) and oxygen reduction reaction (ORR). Herein, the recent research advances regarding porous noble metal nanocatalysts for fuel cell-related reactions are reviewed. In the discussions, the inherent structural features of porous noble metal nanostructures for electrocatalytic reactions, advanced synthetic strategies for the fabrication of porous noble metal nanostructures, and the structure-performance relationships are also provided.

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.

Self-electrochemiluminescence biosensor based on CRISPR/Cas12a and PdCuBP@luminol nanoemitter for highly sensitive detection of cytochrome c oxidase subunit III gene of acute kidney injury

The cytochrome c oxidase subunit III (COX III) gene is a powerful biomarker for the early diagnosis of acute kidney injury. However, current methods for COX III gene detection are usually laborious and time-consuming, with limited sensitivity. Herein, we report a novel self-electrochemiluminescence (ECL) biosensor for highly sensitive detection of the COX III gene based on CRISPR/Cas12a and nanoemitters of luminol-loaded multicomponent metal-metalloid PdCuBP alloy mesoporous nanoclusters. The nanoemitter with excellent self-ECL in neutral media exhibited a high specific surface area for binding luminol and outstanding oxidase-like catalytic activity toward dissolved O₂. Meanwhile, the CRISPR/Cas12a system, as a target-trigger, was employed to specifically recognize the COX III gene and efficiently cleave the interfacial quencher of dopamine-labeled hairpin DNA. As a result, the ECL biosensor showed superior analytical performance for COX III gene detection without exogenous coreactant. Benefiting from the high-efficiency ECL emission of the nanoemitter and Cas12a-mediated interfacial cleavage of the quencher, the developed ECL biosensor exhibited high sensitivity to COX III with a low detection limit of 0.18 pM. The established ECL biosensing method possessed excellent practical performance in urine samples. Meaningfully, the proposed strategy presents promising prospects for nucleic acid detection in the field of clinical diagnostics.

Emerging interstitial/substitutional modification of Pd-based nanomaterials with nonmetallic elements for electrocatalytic applications

Palladium (Pd)-based nanomaterials have been identified as potential candidates for various types of electrocatalytic reaction, but most of them typically exhibit unsatisfactory performances. Recently, extensive theoretical and experimental studies have demonstrated that the interstitial/substitutional modification of Pd-based nanomaterials with nonmetallic atoms (H, B, C, N, P, S) has a significant impact on their electronic structure and thus leads to the rapid development of one kind of promising catalyst for various electrochemical reactions. Considering the remarkable progress in this area, we highlight the most recent progress regarding the innovative synthesis and advanced characterization methods of nonmetallic atom-doped Pd-based nanomaterials and provide insights into their electrochemical applications. What's more, the unique structure- and component-dependent electrochemical performance and the underlying mechanisms are also discussed. Furthermore, a brief conclusion about the recent progress achieved in this field as well as future perspectives and challenges are provided.

Ultrathin Twisty PdNi Alloy Nanowires as Highly Active ORR Electrocatalysts Exhibiting Morphology-Induced Durability over 200 K Cycles

Even though the anion exchange membrane fuel cells have many advantages, the stability of their electrocatalysts for oxygen reduction reaction (ORR) has remained remarkably poor. We report here on the ultrathin twisty PdNi-alloy nanowires (NWs) exhibiting a very low reaction overpotential with an E_1/2 ∼ 0.95 V versus RHE in alkaline media maintained over 200 K cycles, the highest ever recorded for an electrocatalyst. The mass activity of the used NWs is >10 times higher than fresh commercial Pt/C. Therein, Ni improves the Pd d-band center for a more efficient ORR, and its leaching continuously regenerates the surface active sites. The twisty nanowire morphology imparts multiple anchor points on the electrode surface to arrest their detachment or coalescence and extra stability from self-entanglement. The significance of the NW morphology was further confirmed from the high-temperature durability studies. The study demonstrates that tailoring the number of contact points to the electrode-surface may help realize commercial-grade stability in the highly active electrocatalysts.

A dual-signal electrochemical immunosensor for the detection of HPV16 E6 oncoprotein based on PdBP dendritic ternary nanospheres and MBSi-Chi nanocomposites

A dual-signal electrochemical immunosensor was fabricated to detect HPV16 E6 oncoprotein for the first time, which meets the requirements for a quick and sensitive detection.

Mesoporous Noble Metal-Metalloid/Nonmetal Alloy Nanomaterials: Designing Highly Efficient Catalysts

Mesoporous metals have received increasing attention in catalysis and related applications because of their novel physicochemical properties and functional geometric features. Control of multicomponent compositions and crystalline structures of mesoporous metals is critical for their applications. Recently, mesoporous metals have gradually expanded from traditional metal-metal alloys to metal-metalloid/nonmetal alloys with random solids and/or ordered intermetallics. As new, highly efficient nanocatalysts, mesoporous metal-metalloid/nonmetal alloys not only increase the utilization efficiency of precious noble metals and accelerate electron/mass transfer but also introduce new functions and optimize the surface electronic structure of metal sites, all of which enhance their catalytic activity and stability and tune their catalytic selectivity. In this Perspective, we focus on the latest developments in this area, including the findings from our group regarding the rational design and targeted synthesis of mesoporous noble metal-metalloid/nonmetal alloy nanocatalysts. We summarize the current synthetic strategies for mesoporous noble metal-metalloid/nonmetal alloys and discuss key effects of crystalline mesoporosity and metalloid/nonmetal alloys in enhancing catalytic performances of noble metal catalysts. We also describe the current bottlenecks and major challenges to explore further directions in synthesis and applications of mesoporous noble metal-metalloid/nonmetal alloys.

Regulating the Electron Localization of Metallic Bismuth for Boosting CO2 Electroreduction

Electrochemical reduction of CO₂ to formate is economically attractive but improving the reaction selectivity and activity remains challenging. Herein, we introduce boron (B) atoms to modify the local electronic structure of bismuth with positive valence sites for boosting conversion of CO₂ into formate with high activity and selectivity in a wide potential window. By combining experimental and computational investigations, our study indicates that B dopant differentiates the proton participations of rate-determining steps in CO₂ reduction and in the competing hydrogen evolution. By comparing the experimental observations with the density functional theory, the dominant mechanistic pathway of B promoted formate generation and the B concentration modulated effects on the catalytic property of Bi are unravelled. This comprehensive study offers deep mechanistic insights into the reaction pathway at an atomic and molecular level and provides an effective strategy for the rational design of highly active and selective electrocatalysts for efficient CO₂ conversion.

Mesoporosity-Enabled Selectivity of Mesoporous Palladium-Based Nanocrystals Catalysts in Semihydrogenation of Alkynes

We reported mesoporosity engineering as a general strategy to promote semihydrogenation selectivity of palladium (Pd)-based nanobundles catalysts. The best mesoporous PdP displayed full conversion, remarkable activity, excellent selectivity, and high stability in semihydrogenation of 1-phenyl-1-propyne, all of which are remarkably better than commercial Lindlar catalysts. Mechanistic investigations ascribed high semihydrogenation selectivity to continuous crystalline framework and penetrated mesoporous channel of catalysts that weakened the adsorption and interaction capacity of alkenes and thus inhibited over-hydrogenation of alkenes to industrially unfavorable alkanes. Density functional theory calculations further demonstrated that convex crystalline mesoporosity of nanobundles catalysts electronically optimized the coordination environment of Pd active sites and energetically changed hydrogenation trends, resulting in a superior semihydrogenation selectivity to targeted alkenes.

Recent Advances in Electrocatalysts for Proton Exchange Membrane Fuel Cells and Alkaline Membrane Fuel Cells

The rapid progress of proton exchange membrane fuel cells (PEMFCs) and alkaline exchange membrane fuel cells (AMFCs) has boosted the hydrogen economy concept via diverse energy applications in the past decades. For a holistic understanding of the development status of PEMFCs and AMFCs, recent advancements in electrocatalyst design and catalyst layer optimization, along with cell performance in terms of activity and durability in PEMFCs and AMFCs, are summarized here. The activity, stability, and fuel cell performance of different types of electrocatalysts for both oxygen reduction reaction and hydrogen oxidation reaction are discussed and compared. Research directions on the further development of active, stable, and low-cost electrocatalysts to meet the ultimate commercialization of PEMFCs and AMFCs are also discussed.

Structural Modulation on NiCo2 S4 Nanoarray by N Doping to Enhance 2e-ORR Selectivity for Photothermal AOPs and Zn-O2 Batteries*

As a H₂ O₂ generator, a 2e^- oxygen reduction reaction active electrocatalyst plays an important role in the advanced oxidation process to degrade organic pollutants in sewage. To enhance the tendency of NiCo₂ S₄ towards the 2e^- reduction reaction, N atoms are doped in its structure and replace S^2- . The result implies that this weakens the interaction between NiCo₂ S₄ and OOH*, suppresses O-O bond breaking and enhances H₂ O₂ selectivity. This electrocatalyst also shows photothermal effect. Under photothermal heating, H₂ O₂ produced by the oxidation reduction reaction can decompose and releaseOH, which degrades organic pollutants through the advanced oxidation process. Photothermal effect induced by the advance oxidation process shows obvious advantages over the traditional Fenton reaction, such as wide pH adaptation scope and low secondary pollutant due to its Fe²⁺ free character. With Zn as anode and the electrocatalyst as cathode material, a Zn-O₂ battery is assembled. It achieves electricity generation and photothermal effect induced by the advance oxidation process simultaneously.

Recent advances in phosphorus containing noble metal electrocatalysts for direct liquid fuel cells

Direct liquid fuel cells (DLFCs) are considered as satisfactory alternatives to traditional fossil fuels owing to their unique advantages, e.g. environmental friendliness and easy storage. Noble metal catalysts are widely used to improve the efficiency of DLFCs. However, the high cost, low utilization and poor stability of noble metals restricted their practical applications. Therefore, it is of great significance to explore cost-effective electrocatalysts and further improve their electrocatalytic performance. Reducing the content of noble metals by adding low-priced phosphorus (P) has been considered as an effective strategy, which is able to enhance their electrocatalytic activity and anti-poisoning ability through effectively changing the electronic density of active sites. In the past few years, tremendous P containing catalysts have been synthesized and utilized in DLFCs. In this review, we summarize the fundamentals of electrochemical reactions and present recent progress in P containing noble metal catalysts for DLFCs, including the discussion of their shape, composition and the relationship between P and active sites. Finally, the challenges and some potential directions in this field are pointed out.

Nonmetal-doping of noble metal-based catalysts for electrocatalysis

In response to the shortage of fossil fuels, efficient electrochemical energy conversion devices are attracting increasing attention, while the limited electrochemical performance and high cost of noble metal-based electrode materials remain a daunting challenge. The electrocatalytic performance of electrode materials is closely bound with their intrinsic electronic/ionic states and crystal structures. Apart from the nanoscale design and conductive composite strategies, heteroatom doping, particularly for nonmetal doping (e.g., hydrogen, boron, sulfur, selenium, phosphorus, and tellurium), is also another effective strategy to greatly promote the intrinsic activity of the electrode materials by tuning their atomic structures. From the perspective of electrocatalytic reactions, the effective atomic structure regulation could induce additional active sites, create rich defects, and optimize the adsorption capability, thereby contributing to the promotion of the electrocatalytic performance of noble metal-based electrocatalysts. Encouraged by the great progress achieved in this field, we have reviewed recent advancements in nonmetal doping for electrocatalytic energy conversion. Specifically, the doping effect on the atomic structure and intrinsic electronic/ionic state is also systematically illustrated and the relationship with the electrocatalytic performance is also investigated. It is believed that this review will provide guidance for the development of more efficient electrocatalysts.

Atomic Regulation of PGM Electrocatalysts for the Oxygen Reduction Reaction

With the increasing enthusiasm for the hydrogen economy and zero-emission fuel cell technologies, intensive efforts have been dedicated to the development of high-performance electrocatalytic materials for the cathodic oxygen reduction reaction (ORR). Some major fundamental breakthroughs have been made in the past few years. Therefore, reviewing the most recent development of platinum-group-metal (PGM) ORR electrocatalysts is of great significance to pushing it forward. It is known that the ORR on the fuel cell electrode is a heterogeneous reaction occurring at the solid/liquid interface, wherein the electron reduces the oxygen along with species in the electrolyte. Therefore, the ORR kinetic is in close correlation with the electronic density of states and wave function, which are dominated by the localized atomic structure including the atomic distance and coordination number (CN). In this review, the recent development in the regulation over the localized state on the catalyst surface is narrowed down to the following structural factors whereby the corresponding strategies include: the crystallographic facet engineering, phase engineering, strain engineering, and defect engineering. Although these strategies show distinctive features, they are not entirely independent, because they all correlate with the atomic local structure. This review will be mainly divided into four parts with critical analyses and comparisons of breakthroughs. Meanwhile, each part is described with some more specific techniques as a methodological guideline. It is hoped that the review will enhance an insightful understanding on PGM catalysts of ORR with a visionary outlook.

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.

Porous Noble Metal Electrocatalysts: Synthesis, Performance, and Development

Active sites (intrinsic activity, quantity, and distribution), electron transfer, and mass diffusion are three important factors affecting the performance of electrocatalysts. Composed of highly active components which are built into various network structures, porous noble metal is an inherently promising electrocatalysts. In recent years, great efforts have been made to explore new efficient synthesis methods and establish structural-performance relationships in the field of porous noble metal electrocatalysis. In this review, the very recent progress in strategies for preparing porous noble metal, including innovation and deeper understanding of traditional methods is summarized. A discussion of relationship between porous noble metal structure and electrocatalytic performance, such as accessibility of active sites, connectivity of skeleton structures, channels dimensions, and hierarchical structures, is provided.

Mesoporous Palladium-Boron-Sulfur Alloy Nanospheres for Efficient Hydrogen Evolution

Ternary noble metal-metalloid-nonmetal PdBS alloy mesoporous nanospheres (MSs) with three-dimensional central-radial pore channels were prepared for an electrocatalytic hydrogen evolution reaction. The synthesis was performed via precise control in the reduction and nucleation growth of ternary PdBS alloy MSs along confined cylinder mesophases assembled by amphiphilic dioctadecyldimethylammonium chloride. The resultant PdBS alloy MSs disclosed a remarkably improved electrocatalytic performance due to their structural and compositional synergies. This finding extended our knowledge on the rational design and targeted synthesis of novel noble metal-metalloid-nonmetal alloys with desired structures and morphologies for catalysis and other applications.

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.