Highly Dispersed Pd-CeO2 Nanoparticles Supported on N-Doped Core–Shell Structured Mesoporous Carbon for Methanol Oxidation in Alkaline Media

Modulating d-Orbital electronic configuration via metal-metal oxide interactions for boosting electrocatalytic methanol oxidation

Coordinating the interfacial interaction between Pt-based nanoparticles (NPs) and supports is a significant strategy for the modulation of d-orbital electronic configuration and the adsorption behaviors of intermediates, which is of critical importance for boosting electrocatalytic performance. Herein, we demonstrated a specific synergy effect between the ordered PtFe intermetallic and neighboring oxygen vacancies (Ov), which provides an "ensemble reaction pool" to balance the barriers of both the activity, stability, and CO poisoning issues for the methanol oxidation reaction (MOR). In our proposed "ensemble reaction pool", the deprotonation of methanol occurs on the Pt site to form the intermediate *CO, where the strain derived from the PtFe intermetallic could alter the d-orbital electronic configuration of Pt, intrinsically weakening the *CO adsorption energy, and Ov in CeO2 promote hydroxyl species (*OH) adsorption, which will react with *CO, facilitating the dissociative adsorption of *CO, thus cooperatively enhancing the performance of MOR. The X-ray absorption fine structure (XAFS) analyses reveal the electron transfer in CeO2 and then convert Ce4+ to Ce3+. The density functional theory (DFT) calculations revealed that introducing Fe induces strain could modify the d-band center of Pt, and thus lower the energy barrier of the potential-determining step. Meanwhile, the introduction of CeO2 can favor the *OH adsorption, speeding up the oxidation and removal of *CO blocked at the Pt site. Furthermore, the determined atomic arrangement and surface composition of PtFe intermetallic further guarantee the stability of MOR by suppressing less-noble metal into the electrolyte.

Spatial Identification of Mott-Schottky Effect at Electrocatalytic Pd/Metal Oxide Interfaces for the Oxygen Reduction Reaction

To elucidate the microstructure and charge transfer behavior at the interface of Pd/metal oxide semiconductor (MOS) catalysts and systematically explore the crucial role of the Mott-Schottky effect in the oxygen reduction reaction (ORR) electrocatalysis process, this study established a testing system for spatially identifying Mott-Schottky effects and electronic properties at Pd/MOS interfaces, leveraging highly sensitive Kelvin probe force microscopy (KPFM). This system enabled visualization and quantification of the surface potential difference and Mott-Schottky barrier height (ΦSBH) at the Pd/MOS heterojunction interfaces. Furthermore, a series of Pd/MOS Mott-Schottky catalysts were constructed based on differences in work functions between Pd and n-type MOS. The abundant oxygen vacancies in these catalysts facilitated the adsorption and activation of oxygen molecules. Notably, the intensity of the built-in electric field in the Pd/MOS Mott-Schottky catalysts was calculated through surface potential and zeta potential analysis, systematically correlating the Mott-Schottky effect at the heterojunction interface of Pd/MOS with ORR activity and kinetics. By comprehensively exploring the correlation between the Mott-Schottky effect and ORR performance in Pd/MOS catalysts using the KPFM testing system, this study provides necessary tools and approaches for a deep understanding of heterogeneous interface charge transfer mechanisms, as well as for optimizing catalyst design and enhancing ORR performance.

Advancements in Noble Metal-Decorated Porous Carbon Nanoarchitectures: Key Catalysts for Direct Liquid Fuel Cells

Noble-metal nanocrystals have emerged as essential electrode materials for catalytic oxidation of organic small molecule fuels in direct liquid fuel cells (DLFCs). However, for large-scale commercialization of DLFCs, adopting cost-effective techniques and optimizing their structures using advanced matrices are crucial. Notably, noble metal-decorated porous carbon nanoarchitectures exhibit exceptional electrocatalytic performances owing to their three-dimensional cross-linked porous networks, large accessible surface areas, homogeneous dispersion (of noble metals), reliable structural stability, and outstanding electrical conductivity. Consequently, they can be utilized to develop next-generation anode catalysts for DLFCs. Considering the recent expeditious advancements in this field, this comprehensive review provides an overview of the current progress in noble metal-decorated porous carbon nanoarchitectures. This paper meticulously outlines the associated synthetic strategies, precise microstructure regulation techniques, and their application in electrooxidation of small organic molecules. Furthermore, the review highlights the research challenges and future opportunities in this prospective research field, offering valuable insights for both researchers and industry experts.

Rare earth oxide based electrocatalysts: synthesis, properties and applications

As an important strategic resource, rare earths (REs) constitute 17 elements in the periodic table, namely 15 lanthanides (Ln) (La-Lu, atomic numbers from 57 to 71), scandium (Sc, atomic number 21) and yttrium (Y, atomic number 39). In the field of catalysis, the localization and incomplete filling of 4f electrons endow REs with unique physical and chemical properties, including rich electronic energy level structures, variable coordination numbers, etc., making them have great potential in electrocatalysis. Among various RE catalytic materials, rare earth oxide (REO)-based electrocatalysts exhibit excellent performances in electrocatalytic reactions due to their simple preparation process and strong structural variability. At the same time, the electronic orbital structure of REs exhibits excellent electron transfer ability, which can reduce the band gap and energy barrier values of rate-determining steps, further accelerating the electron transfer in the electrocatalytic reaction process; however, there is a lack of systematic review of recent advances in REO-based electrocatalysis. This review systematically summarizes the synthesis, properties and applications of REO-based nanocatalysts and discusses their applications in electrocatalysis in detail. It includes the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR), methanol oxidation reaction (MOR), nitrogen reduction reaction (NRR) and other electrocatalytic reactions and further discusses the catalytic mechanism of REs in the above reactions. This review provides a timely and comprehensive summary of the current progress in the application of RE-based nanomaterials in electrocatalytic reactions and provides reasonable prospects for future electrocatalytic applications of REO-based materials.

Interface Charge Distribution Engineering of Pd-CeO2 /C for Efficient Carbohydrazide Oxidation Reaction

Carbohydrazide electrooxidation reaction (COR) is a potential alternative to oxygen evolution reaction in water splitting process. However, the sluggish kinetics process impels to develop efficient catalysts with the aim of the widespread use of such catalytic system. Since COR concerns the adsorption/desorption of reactive species on catalysts, the electronic structure of electrocatalyst can affect the catalytic activity. Interface charge distribution engineering can be considered to be an efficient strategy for improving catalytic performance, which facilitates the cleavage of chemical bond. Herein, highly dispersed Pd nanoparticles on CeO2 /C catalyst are prepared and the COR catalytic performance is investigated. The self-driven charge transfer between Pd and CeO2 can form the local nucleophilic and electrophilic region, promoting to the adsorption of electron-withdrawing and electron-donating group in carbohydrazide molecule, which facilitates the cleavage of C-N bond and the carbohydrazide oxidation. Due to the local charge distribution, the Pd-CeO2 /C exhibits superior COR catalytic activity with a potential of 0.27 V to attain 10 mA cm-2 . When this catalyst is used for energy-efficient electrolytic hydrogen production, the carbohydrazide electrolysis configuration exhibits a low cell voltage (0.6 V at 10 mA cm-2 ). This interface charge distribution engineering can provide a novel strategy for improving COR catalytic activity.

Cerium oxide boosted CoFe-N codoped carbon nanotubes with abundant oxygen-vacancies toward efficient oxygen reduction and methanol oxidation reaction

In this study, we designed a novel strategy that utilizes N-doped carbon nanotubes as the chemical bond supporter to stabilize ultrafine CoFe alloy and introduces secondary CeO2 active sites into the hybrid, resulting in the formation of CeO2/CoFe-NCNTs heterostructures with exceptional bifunctional electrocatalytic capabilities. To be specific, solution dispersion and high-temperature calcination methods were employed to create the CoFe-NCNTs active sites through the introduction of ethylenediamine into the network interstitials of Co-EDTA and Fe-EDTA. The CeO2/CoFe-NCNTs hybrid not only promotes oxygen absorption and conversion of intermediates, but also accelerates charge transfer capability, thus enhancing oxygen reduction reaction (ORR) performance, while simultaneously inducing boosted the methanol oxidation reaction (MOR) activity. Moreover, the well-dispersed CoFe nanoparticles within the hybrid hold significant potential for establishing metal-nitrogen bonds with the N-doped carbon nanotube network, resulting in efficient catalytic behavior driven by synergistic effects with CeO2 nanoparticles, which contributes to reactant activation. As expected, the resultant CeO2/CoFe-NCNTs-2 exhibits remarkable electrocatalytic performance, with a current density of 281.40 mA cm-2 at a scan rate of 200 mV s-1 and a low Tafel slope (71.3 mV dec-1) for MOR, as well as achieving excellent half-wave potential and onset potential values of 0.834 and 0.90 V (vs. RHE) for ORR. Additionally, it exhibits durable cycle stability for both MOR and ORR, retaining 92.8% and 96.4% of its initial current density during the I-t test, respectively. This work establishes a highly efficient bifunctional earth-abundant electrocatalysts for both anode and cathode reactions in methanol fuel cells.

Interfacial engineering of nickel selenide with CeO2 on N-doped carbon nanosheets for efficient methanol and urea electro-oxidation

The design of low cost, high efficiency electrocatalysts for methanol oxidation reactions (MOR) and urea oxidation reactions (UOR) is a pressing need to address the energy crisis and water pollution. In the present work, we developed Cerium dioxide (CeO2) and nickel selenide (Ni0.85Se) nanoparticles integrated into three-dimensional N-doped carbon nanosheets to be used as efficient and stable bifunctional electrocatalysts for MOR and UOR. By optimizing the selenization temperature, the CeO2-modified Ni0.85Se obtained at selenization temperature of 550 °C (CeO2-Ni0.85Se-550-NC) has the best MOR and UOR electrochemical performance. The CeO2-Ni0.85Se-550-NC potential only requires 1.309 V (MOR) and 1.294 V (UOR) to reach 10 mA cm-2, respectively. The DFT study reveals that CeO2-Ni0.85Se-550-NC has the best reaction path with the synergistic effect between CeO2 and Ni0.85Se. The outstanding catalytic performance of CeO2-Ni0.85Se-550-NC may be due to the cointeraction between CeO2 and Ni0.85Se, allowing more defects that function as catalytic sites while promoting fast electron transfer in the N-doped carbon substrate.

Defect-Engineered Charge Transfer in a PtCu/PrxCe1-xO2 Carbon-Free Catalyst for Promoting the Methanol Oxidation and Oxygen Reduction Reactions

Platinum (Pt) and Pt-based alloys have been extensively studied as efficient catalysts for both the anode and cathode of direct methanol fuel cells (DMFC). Defect engineering has been revealed to be practicable in tuning the charge transfer between Pt and transition metals/supports, which leads to the charge density rearrangement and facilitates the electrocatalytic performance. Herein, Pr-doped CeO2 nanocubes were used as the noncarbon support of a PtCu catalyst. The concentration and structure of oxygen vacancy (Vo) defects were engineered by Pr doping. Besides the Vo monomer, the oxygen vacancy with a linear structure is also observed, leading to the one-dimensional PtCu. The Vo concentration shows the volcanic scenario as Pr increased. Accordingly, the activities of PtCu/PrxCe1-xO2 toward methanol oxidation and oxygen reduction reactions exhibit the volcanic scenario. PtCu/Pr0.15Ce0.85O2 exhibits the optimal catalytic performance with the specific activity 3.57 times higher than that of Pt/C toward MOR and 1.34 times higher toward ORR. The MOR and ORR mass activities of PtCu/Pr0.15Ce0.85O2 reached 1.05 and 0.12 A·mg-1, which are 3.09 and 0.92 times the values of Pt/C, respectively. The abundant Vo afforded surplus electrons, which tailored the electron transfer between PtCu and PrxCe1-xO2, leading to enhanced catalytic performance of PtCu/PrxCe1-xO2. DFT calculations on PtCu/Pr0.15Ce0.85O2 revealed that Pr doping reduced the band gap of CeO2 and lowered the overpotential.

Ni dispersed ultrathin carbon nanosheets as bi-functional oxygen electrocatalyst induced from graphite-like porous supramolecule

Excellent porosity and accessibility are key requirements during carbon-based materials design for energy conversion applications. Herein, a Ni-based porous supramolecular framework with graphite-like morphology (Ni-SOF) was rationally designed as a carbon precursor. Ultrathin carbon nanosheets dispersed with Ni nanoparticles and Ni-Nx sites (Ni@NiNx-N-C) were obtained via in-situ exfoliation during pyrolysis. Due to the hetero-porous structure succeeding from Ni-SOF, the Ni@NiNx-N-C catalyst showed outstanding bifunctional oxygen electrocatalytic activity with a narrow gap of 0.69 V between potential to deliver 10 mA cm-2 oxygen evolution and half-wave potential of oxygen reduction reaction, which even surpassed the Pt/C + IrO2 pair. Therefore, the corresponding zinc-air battery exhibited excellent power output and stability. The multiple Ni-based active sites, the unique 2D structure with a high graphitization degree and large specific surface area synergistically contributed to the excellent bifunctional electrocatalytic activity of Ni@NiNx-N-C. This work provided a novel viewpoint for the development of carbon-based electrocatalyst.

Electro-oxidation Reaction of Methanol over Reducible Ce1-x-yNixSryO2-δ: A Mechanistic Probe of Participation of Lattice Oxygen

Methanol oxidation reaction crucially depends on the formation of -OOH species over the catalyst's surface. Ni-based catalysts are by far the choice of materials, where the redox couple of Ni²⁺/Ni³⁺ facilitates the formation of -OOH species by surface reconstructions. However, it is challenging to oxidize Ni²⁺ as it generates charge-transfer orbitals near the Fermi energy level. One possible solution is to substitute Ni²⁺ with a reducible oxide support, which will not only facilitate the Ni²⁺ → Ni³⁺ oxidation but also adsorb oxygenated species like -OOH at a lower potential owing to its oxophilicity. This work shows with the help of structural and surface studies that the reducible CeO₂ support in Ni and Sr co-doped Ce_1-x-yNi_xSr_yO_2-δ solid solution can easily facilitate Ni²⁺ → Ni³⁺ oxidation as well as evolution of lattice oxygen during the methanol oxidation reaction. While the Ni³⁺ species helped in formation of -OOH surface intermediates, the evolved lattice oxygen eased the CO oxidation process in order to bring out the better CO-tolerant methanol oxidation activity over Ce_1-x-yNi_xSr_yO_2-δ. The study shows the unique importance of the electronic interactions between the active site and support and involvement of lattice oxygen in the methanol oxidation reaction.

Nickel -supported PdM (M = Au and Ag) nanodendrites as formate oxidation (electro)catalytic anodes for direct fuel cells and hydrogen generation at room temperature

The study provides a proof of concept for the first time that unique palladium-gold (PdAu) and palladium-silver (PdAg) nanodendrites are bifunctional catalytic active sites for formate oxidation reactions (FORs) and formate dehydrogenation reactions (FDRs). The unique nanodendritic structure was developed via a simple galvanic displacement reaction for the direct growth of PdAu and PdAg nanodendrites on a nickel foam (PdAu/NiNF and PdAg/NiNF). These PdAu/NiNF and PdAg/NiNF electrodes exhibited 2.32 and 1.59 times higher specific activity than that of the commercial Pd/C electrode and promising stability toward FORs. Moreover, the PdAu/NiNF and PdAg/NiNF nanodendrites were also highly active and selective catalysts for hydrogen generation from a formate solution with turnover frequency (TOF) values of 311 h^-1 and 287 h^-1 respectively. Impressively, a passive air-breathing formate fuel cell with PdAu/NiNF used as an anode can yield an open-circuit voltage of 1.12 V and a peak power density of 21.7 mW cm^-2, which outperforms most others reported in the literature. PdAu and PdAg nanodendritic catalysts supported on a nickel foam demonstrate an open structure and uniform catalyst distribution and offer a promising nanoalloy for air-breathing formate fuel cells and on-site chemical hydrogen production systems.

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.

Toward Electrocatalytic Methanol Oxidation Reaction: Longstanding Debates and Emerging Catalysts

The study of direct methanol fuel cells (DMFCs) has lasted around 70 years, since the first investigation in the early 1950s. Though enormous effort has been devoted in this field, it is still far from commercialization. The methanol oxidation reaction (MOR), as a semi-reaction of DMFCs, is the bottleneck reaction that restricts the overall performance of DMFCs. To date, there has been intense debate on the complex six-electron reaction, but barely any reviews have systematically discussed this topic. To this end, the controversies and progress regarding the electrocatalytic mechanisms, performance evaluations as well as the design science toward MOR electrocatalysts are summarized. This review also provides a comprehensive introduction on the recent development of emerging MOR electrocatalysts with a focus on the innovation of the alloy, core-shell structure, heterostructure, and single-atom catalysts. Finally, perspectives on the future outlook toward study of the mechanisms and design of electrocatalysts are provided.

Carbon-Supported PdCu Alloy as Extraordinary Electrocatalysts for Methanol Electrooxidation in Alkaline Direct Methanol Fuel Cells

Palladium (Pd) nanostructures are highly active non-platinum anodic electrocatalysts in alkaline direct methanol fuel cells (DMFCs), and their electrocatalytic performance relies highly on their morphology and composition. This study reports the preparation, characterizations, and electrocatalytic properties of palladium-copper alloys loaded on the carbon support. XC-72 was used as a support, and hydrazine hydrate served as a reducing agent. Pd_xCu_y/XC-72 nanoalloy catalysts were prepared in a one-step chemical reduction process with different ratios of Pd and Cu. A range of analytical techniques was used to characterize the microstructure and electronic properties of the catalysts, including transmission electron microscopy (TEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma emission spectroscopy (ICP-OES). Benefiting from excellent electronic structure, Pd₃Cu₂/XC-72 achieves higher mass activity enhancement and improves durability for MOR. Considering the simple synthesis, excellent activity, and long-term stability, Pd_xCu_y/XC-72 anodic electrocatalysts will be highly promising in alkaline DMFCs.

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

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

Fabrication of Mn3O4-CeO2-rGO as Nanocatalyst for Electro-Oxidation of Methanol

Recently, the use of metal oxides as inexpensive and efficient catalysts has been considered by researchers. In this work, we introduce a new nanocatalyst including a mixed metal oxide, consisting of manganese oxide, cerium oxide, and reduced graphene oxide (Mn₃O₄-CeO₂-rGO) by the hydrothermal method. The synthesized nanocatalyst was evaluated for the methanol oxidation reaction. The synergetic effect of metal oxides on the surface of rGO was investigated. Mn₃O₄-CeO₂-rGO showed an oxidation current density of 17.7 mA/cm² in overpotential of 0.51 V and 91% stability after 500 consecutive rounds of cyclic voltammetry. According to these results, the synthesized nanocatalyst can be an attractive and efficient option in the methanol oxidation reaction process.

Pt/Mn3O4 cubes with high anti-poisoning ability for C1 and C2 alcohol fuel oxidation

Pt particles anchored onto Mn₃O₄ cubes were found to have high anti-CO poisoning abilities for C1- and C2-alcohol fuel oxidations in acid electrolyte, due to an electronic effect that enriched the surfaces of the Pt particles with electrons and due to the oxophilicity of Mn₃O₄ in the system.

High-Entropy Alloys for Electrocatalysis: Design, Characterization, and Applications

High-entropy alloys (HEAs) are expected to function well as electrocatalytic materials, owing to their widely adjustable composition and unique physical and chemical properties. Recently, HEA catalysts are extensively studied in the field of electrocatalysis; this motivated the authors to investigate the relationship between the structure and composition of HEAs and their electrocatalytic performance. In this review, the latest advances in HEA electrocatalysts are systematically summarized, with special focus on nitrogen fixation, the carbon cycle, water splitting, and fuel cells; in addition, by combining this with the characterization and analysis of HEA microstructures, rational design strategies for optimizing HEA electrocatalysts, including controllable preparation, component regulation, strain engineering, defect engineering, and theoretical prediction are proposed. Moreover, the existing issues and future trends of HEAs are predicted, which will help further develop these high-entropy materials.

Pd17Se15 alloy on Se sphere with high anti-poisoning ability for alcohol fuel electrooxidation

Electron-deficient effect of Pd in the Pd17Se15 catalyst effectively weakens the adsorption of CO poisoning species and enhances the electrocatalytic performance of alcohol electrooxidation in an alkaline medium.

ZrO2/CeO2/polyacrylic acid nanocomposites with alkaline phosphatase-like activity for sensing

In the present work, we synthesized ZrO₂/CeO₂/polyacrylic acid (PAA) nanocomposites (nanozyme) with phosphatase-like activity. ZrO₂ evenly distributed in CeO₂ nanorods considered as lewis acids to enhance the phosphatase-like activity of CeO₂ nanorods. Furthermore, PAA was used to coat ZrO₂/CeO₂/ nanorods and improve the dispersion, stability and robustness. The ZrO₂/CeO₂/PAA nanocomposites had 100% enhanced phosphatase-like activity compared with CeO₂ nanorods and excellent adaptability in a wide pH range from 4.0 to 12.0. ZrO₂/CeO₂/PAA nanocomposites could hydrolyze methyl parathion (MP) to p-nitrophenol (p-NP) with bright yellow color for colorimetric detection. The developed colorimetric detection system showed a linear response from 7.60 × 10^-11-7.60 × 10^-8 M with a detection limit of 0.021 nM and was successfully applied for the determination of MP in corn samples.

A theoretical study of the electrochemical reduction of CO2 on cerium dioxide supported palladium single atoms and nanoparticles

Pd/CeO₂ catalysts show superior catalytic performance owing to their optimal cycling activity and stability. In this study, single-atom Pd and eight-atom Pd nanoparticle clusters were supported on the surface of CeO₂(110) to investigate the effect of loaded-metal size on the catalytic performance of the Pd-CeO₂ system for CO₂ reduction. We investigated the CO₂ reduction reaction (CRR) that produces C₁ products (CO, HCOOH, CH₃OH, and CH₄) on Pd₈/CeO₂ and Pd/CeO₂ by density functional theory. The structures, CO₂ adsorption configurations, and CO₂ reduction mechanisms of these two electrocatalysts were systematically studied. Subsequently, different reduction pathways on Pd₈/CeO₂ and Pd/CeO₂ were investigated to identify the optimal reaction pathway for further assessment. The results showed that both of these catalysts are more selective towards the production of CH₃OH than CH₄. Moreover, compared to Pd/CeO₂ and Pd₄/CeO₂ (from a previously reported study) the production of CH₃OH via the CRR on Pd₈/CeO₂ exhibited the lowest limiting potential. These results demonstrate the superiority of Pd₈/CeO₂ as an electrocatalyst for the electrochemical reduction of CO₂ to CH₃OH.

Advanced Nanocarbons for Enhanced Performance and Durability of Platinum Catalysts in Proton Exchange Membrane Fuel Cells

Insufficient stability of current carbon supported Pt and Pt alloy catalysts is a significant barrier for proton-exchange membrane fuel cells (PEMFCs). As a primary degradation cause to trigger Pt nanoparticle migration, dissolution, and aggregation, carbon corrosion remains a significant challenge. Compared with enhancing Pt and PtM alloy particle stability, improving support stability is rather challenging due to carbon's thermodynamic instability under fuel cell operation. In recent years, significant efforts have been made to develop highly durable carbon-based supports concerning innovative nanostructure design and synthesis along with mechanistic understanding. This review critically discusses recent progress in developing carbon-based materials for Pt catalysts and provides synthesis-structure-performance correlations to elucidate underlying stability enhancement mechanisms. The mechanisms and impacts of carbon support degradation on Pt catalyst performance are first discussed. The general strategies are summarized to tailor the carbon structures and strengthen the metal-support interactions, followed by discussions on how these designs lead to enhanced support stability. Based on current experimental and theoretical studies, the critical features of carbon supports are analyzed concerning their impacts on the performance and durability of Pt catalysts in fuel cells. Finally, the perspectives are shared on future directions to develop advanced carbon materials with favorable morphologies and nanostructures to increase Pt utilization, strengthen metal-support interactions, facilitate mass/charge transfer, and enhance corrosion resistance.

Efficient synergism of V2O5 and Pd for alkaline methanol electrooxidation

Efficient synergism of high valence state V and Pd nanoparticles imparted their high catalytic performance and anti-poisoning ability for alkaline methanol electrooxidation.

Stability-Enhanced α-Ni(OH)2 Pillared by Metaborate Anions for Pseudocapacitors

α-Ni(OH)₂ is an ideal candidate material for a supercapacitor except for its low conductivity and poor stability. In this work, BO₂^--intercalated α-Ni_xCo_(1-x)(OH)₂ is synthesized by a hydrothermal method at a low cost. The Co dopant can decrease the charge-transfer resistance and enhance the cyclic stability. The special unsaturated electronic state of BO₂^- enhances the bonding with metal ions and attracts water molecules. Thus, the BO₂^- ions support the hydroxide layers as pillars and create efficient paths for proton transportation, optimizing the utilization of α-Ni(OH)₂. The three-dimensional (3D) flowerlike morphology supplies an enormous number of active sites, and r-GO is added to improve the conductivity. As a result, the modified α-Ni(OH)₂ exhibits the specific capacitance of 2179, 1592, and 1423 F·g^-1 at 1, 20, and 40 A·g^-1, respectively, showing improved rate performance. Matching with the commercial activated carbon (AC) as an anode, the asymmetric capacitor delivers an energy density of 40.66 W·h·kg^-1 when its power density is 187.06 W·kg^-1. Meanwhile, it retains 81.5% capacitance of the initial cycle at 5 A·g^-1 after 3000 cycles. With conductivity enhanced and structure stabilized, the modified α-Ni(OH)₂ confronts broader fields of application.

Porous PdAg alloy nanostructures with a concave surface for efficient electrocatalytic methanol oxidation

Tuning the composition and surface structure of the metal nanocrystals offered viable avenues for enhancing catalytic performances. Herein, we report a facile one-pot strategy for the formation of PdAg porous alloy nanostructures (PANs) with a concave surface. Due to their highly open nanostructures and tunable d-band center features, PdAg PANs exhibit superior electrocatalytic activity and long-term durability than Pd nanoparticles (NPs) and Pd/C for methanol oxidation reaction (MOR) in alkaline media. Our results provide a feasible and efficient approach for the controlled synthesis of high-performance Pd-based nanomaterials for alkaline MOR.

Hollow Pd/Te nanorods for the effective electrooxidation of methanol

Methanol electrooxidation is significant in realizing effective C1 liquid fuel applications. Herein, hollow Pd/Te nanorods were fabricated and evaluated for methanol oxidation, and they were found to exhibit high catalytic efficiency for methanol oxidation in alkaline electrolyte compared to Pd or Pd/C catalysts. The hybrid structure of hexagonal crystal Te and face-centered cubic Pd was formed by microwave assisted Pd nanoparticle deposition over the surface of Te nanorods. Strong electronic effects and facile oxophilic properties were indicated in the Pd/Te system by spectroscopic analysis, which mainly accounts for the high catalytic performance for methanol oxidation. Specifically, they showed a peak current density of 90.1 mA cm^-2 for methanol oxidation, around 3.5 times higher than that of commercial Pd/C (26.3 mA cm^-2). High catalytic stability was also observed for Pd/Te, with a current retention of 64.3% after 3600 s of chronoamperometric testing, much higher than for Pd catalysts (20.1%). High anti-CO poisoning ability of the Pd/Te catalyst was demonstrated in the CO-stripping voltammetry results, and faster catalytic kinetics were also observed for this catalyst system. The electron-rich state of Pd and high active site exposure are responsible for the high performance of the Pd/Te catalyst in methanol oxidation.

Tunable Electronic Metal-Support Interactions on Ceria-Supported Noble-Metal Nanocatalysts in Controlling the Low-Temperature CO Oxidation Activity

A fundamental study on the metal-support interactions of supported metal catalysts is of great importance for developing heterogeneous catalysts with high performance, is still attracting and challenging in many heterogeneous catalytic reactions. In this work, we report the catalytic performances of CeO₂-supported noble-metal catalysts among single atoms, subnanoclusters (∼1 nm), and nanoparticles (2.2-2.7 nm) upon low-temperature CO oxidation reaction between 50 and 250 °C. The subnanoclusters and nanoparticles of Ru, Rh, and Ir showed much higher activities than those of the single atoms, while a Pd single-atom catalyst was more active than Pd subnanoclusters and nanoparticles. According to the results of multiple ex situ and in situ characterizations, the much different activities of Ru, Rh, Ir, and Pd were derived from the alterable electronic metal-support interactions (EMSI), which determine the concurrent reaction pathway including the famous Mars van Krevelen mechanism and carbonate-intermediate route on the most active metal sites of M^δ+ (0 < δ < 1) for Ru, Rh, and Ir and Pd²⁺ for Pd. Also, the moderate EMSI of CeO₂-supported Rh subnanoclusters furthest benefited activation of the adsorbed CO molecule and ensured it the highest activity among CeO₂-supported Ru, Rh, and Ir catalysts with similar metal deposit sizes.

Flexible synthesis of Au@Pd core-shell mesoporous nanoflowers for efficient methanol oxidation

The design of bimetallic core-shell nanostructures with mesoporous surfaces is considered significant to strengthen the catalytic activity and stability for direct methanol fuel cells. Here, we report a flexible method to synthesize Au@Pd core-shell mesoporous nanoflowers (Au@mPd NFs) with Au core coated with mesoporous Pd nano-petals, in which polymeric micelle-assembled structures are used as templates to induce the formation of mesopores. Benefiting from the electronic and structural effects, Au@mPd NFs show excellent electrocatalytic activity and stability for methanol oxidation reaction in alkaline electrolytes. This study demonstrates a versatile strategy for the fabrication of core-shell mesoporous nanoflowers with adjustable composition.

Advanced Electrocatalysis for Energy and Environmental Sustainability via Water and Nitrogen Reactions

Clean and efficient energy storage and conversion via sustainable water and nitrogen reactions have attracted substantial attention to address the energy and environmental issues due to the overwhelming use of fossil fuels. These electrochemical reactions are crucial for desirable clean energy technologies, including advanced water electrolyzers, hydrogen fuel cells, and ammonia electrosynthesis and utilization. Their sluggish reaction kinetics lead to inefficient energy conversion. Innovative electrocatalysis, i.e., catalysis at the interface between the electrode and electrolyte to facilitate charge transfer and mass transport, plays a vital role in boosting energy conversion efficiency and providing sufficient performance and durability for these energy technologies. Herein, a comprehensive review on recent progress, achievements, and remaining challenges for these electrocatalysis processes related to water (i.e., oxygen evolution reaction, OER, and oxygen reduction reaction, ORR) and nitrogen (i.e., nitrogen reduction reaction, NRR, for ammonia synthesis and ammonia oxidation reaction, AOR, for energy utilization) is provided. Catalysts, electrolytes, and interfaces between the two within electrodes for these electrocatalysis processes are discussed. The primary emphasis is device performance of OER-related proton exchange membrane (PEM) electrolyzers, ORR-related PEM fuel cells, NRR-driven ammonia electrosynthesis from water and nitrogen, and AOR-related direct ammonia fuel cells.

Rod-like MnO2 boost Pd/reduced graphene oxide nanocatalyst for ethylene glycol electrooxidation

Anode catalyst is one of the core components of fuel cell, but its poor catalytic activity, short lifespan, and high price are tricky problems to the commercialization of fuel cell. Herein, a novel rod-like MnO₂ decorated reduced graphene oxide (RGO) supported Pd hybrid (Pd/RGO-MnO₂) has been designed, which manifests more negative onset oxidation potential, higher peak current density, and better long-term stability relative to Pd/RGO and pure Pd catalysts when serving for ethylene glycol electrooxidation. This enhancement may be due to the addition of MnO₂, which can effectively promote the adsorption of hydroxyl at a lower potential and produce a strong electronic interaction with Pd, as confirmed by X-ray photoelectron spectroscopy (XPS) technique. In view of its excellent performance and low cost, Pd/RGO-MnO₂ is considered to be a potential and effective anode catalyst for DEGFCs.

Nitrogen modulated NiMoO4 with enhanced activity for the electrochemical oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

NiMoO4 catalyst modified with nitrogen can significantly improve the electrocatalytic oxidation performance of HMF to FDCA.

In situ electrochemical redox tuning of Pd-Co hybrid electrocatalysts for high-performance methanol oxidation: Strong metal-support interaction

Construction of strong metal-support interaction (SMSI) is of fundamental interest in the preparation of supported metal nanoparticle catalysts with enhanced catalytic activity. Herein, we report a facile in situ electrochemical redox tuning approach to build strong interactions between metals and supports. As for a typical example, a composite electrocatalyst of Pd-Co hybrid nanoparticles directly developed on Ni substrate is found to follow a distinct surface self-reconstruction process in alkaline media via an in situ electrochemical redox procedure, which results in structural transition from the original nanoparticles (NPs) to nanosheets (NSs) coupled with a phase transformation of the Co component, Co → CoO/Co(OH)₂. The SMSI is observed in the electrochemically tuned Pd-Co hybrid system and leads to significantly enhanced catalytic activity for methanol oxidation reaction (MOR) due to the modified atomic/electronic structure, increased surface area, and more exposed electroactive sites. Compared with commercial Pd/C catalyst, the electrochemically tuned Pd-Co hybrid catalyst with SMSI exhibits superior catalytic activity (2330 mA∙mg_Pd^-1) and much better stability (remains 503 mA∙mg_Pd^-1 after 1000 cycles and 172 mA∙mg_Pd^-1 after 5000 s), and therefore has great potential in practical applications.

Noble Metal Aerogels

Noble metal-based nanomaterials have been a hot research topic during the past few decades. Particularly, self-assembled porous architectures have triggered tremendous interest. At the forefront of porous nanostructures, there exists a research endeavor of noble metal aerogels (NMAs), which are unique in terms of macroscopic assembly systems and three-dimensional (3D) porous network nanostructures. Combining excellent features of noble metals and the unique structural traits of porous nanostructures, NMAs are of high interest in diverse fields, such as catalysis, sensors, and self-propulsion devices. Regardless of these achievements, it is still challenging to rationally design well-tailored NMAs in terms of ligament sizes, morphologies, and compositions and profoundly investigate the underlying gelation mechanisms. Herein, an elaborate overview of the recent progress on NMAs is given. First, a simple description of typical synthetic methods and some advanced design engineering are provided, and then, the gelation mechanism models of NMAs are discussed in detail. Furthermore, promising applications particularly focusing on electrocatalysis and biosensors are highlighted. In the final section, brief conclusions and an outlook on the existing challenges and future chances of NMAs are also proposed.

Biomimetic Au/CeO2 Catalysts Decorated with Hemin or Ferrous Phthalocyanine for Improved CO Oxidation via Local Synergistic Effects

Biomimetic catalysts have drawn broad research interest owing to both high specificity and excellent catalytic activity. Herein, we report a series of biomimetic catalysts by the integration of biomolecules (hemin or ferrous phthalocyanine) onto well-defined Au/CeO₂, which leads to the high-performance CO oxidation catalysts. Strong electronic interactions among the biomolecule, Au, and CeO₂ were confirmed, and the CO uptake over hemin-Au/CeO₂ was roughly about 8 times greater than Au/CeO₂. Based on the Au/CeO₂(111) and hemin-Au/CeO₂(111) models, the density functional theory calculations reveal the mechanisms of the biomolecules-assisted catalysis process. The theoretical prediction suggests that CO and O₂ molecules preferentially bind to the surface of noncontacting Au atoms (low-coordinated sites) rather than the biomolecule sites, and the accelerating oxidation of Au-bound CO occurs via either the Langmuir-Hinshelwood mechanism or the Mars-van Krevelen mechanism. Accordingly, the findings provide useful insights into developing biomimetic catalysts with low cost and high activity.

Accelerating charge transfer to enhance H2 evolution of defect-rich CoFe2O4 by constructing a Schottky junction

We demonstrate a charge transfer boosted hydrogen (H2) evolution of transition metal oxides via a Schottky junction. The FeNi and metallic defect-rich CoFe2O4 (DCF) as well as semiconducting nitrogen-doped carbon (NC), named as FeNi/DCF/NC, possessed only 6.5% charge transfer resistance of DCF. Theoretical calculations indicate that the enhanced electron movement happened from FeNi/DCF to NC. The H2 evolution activity of FeNi/DCF/NC showed 5.8-fold improvement compared to that of DCF at the overpotential of 400 mV in 1.0 M KOH. This work provides an effective way to enhance the electrocatalytic activity of oxides for the H2 evolution reaction and related reactions.