Nanoporous Au Thin Films on Si Photoelectrodes for Selective and Efficient Photoelectrochemical CO2 Reduction

An Si photoelectrode with a nanoporous Au thin film for highly selective and efficient photoelectrochemical (PEC) CO₂ reduction reaction (CO₂RR) is presented. The nanoporous Au thin film is formed by electrochemical reduction of an anodized Au thin film. The electrochemical treatments of the Au thin film critically improve CO₂ reduction catalytic activity of Au catalysts and exhibit CO Faradaic efficiency of 96% at 480 mV of overpotential. To apply the electrochemical pretreatment of Au films for PEC CO₂RR, a new Si photoelectrode design with mesh‐type co‐catalysts independently wired at the front and the back of the photoelectrode is demonstrated. Due to the superior CO₂RR activity of the nanoporous Au mesh and high photovoltage from Si, the Si photoelectrode with the nanoporous Au thin film mesh shows conversion of CO₂ to CO with 91% Faradaic efficiency at positive potential than the CO₂/CO equilibrium potential.     

Air Plasma Activation of Catalytic Sites in a Metal‐Cyanide Framework for Efficient Oxygen Evolution Reaction

Targeted activation of highly ordered and distributed metal sites in nanoporous frameworks is a generic strategy to develop high‐performance catalysts. The key challenge is to achieve such activation without damaging the frameworks. Here it is demonstrated that atmospheric‐pressure low‐temperature plasma generated in air improve catalytic properties of an Fe/Co bimetallic cyanide framework through the specific “soft” incorporation of reactive oxygen species without affecting the framework structure. The bonding and oxidative states of the high‐density catalytic metal sites in the framework are modified while the nanoporous nature of the framework is retained, which leads to superior catalytic performance for the oxygen evolution reaction at high current densities close to the operation conditions of commercial alkaline electrolyzers.     

Electrodeposited MnOx Films from Ionic Liquid for Electrocatalytic Water Oxidation

A novel method for the electrodeposition of highly active water oxidation catalysts is described. The manganese oxide (MnO_x) films are electrodeposited on fluorine tin oxide (FTO) glass substrate at high temperature (120 °C) from an ionic liquid electrolyte (ethylammonium nitrate). A range of analytical techniques, including X‐ray absorption spectroscopy (XAS), X‐ray diffraction (XRD), and energy‐dispersive X‐ray analyzer (EDX), indicate that the valence state of manganese in the deposited films can be controlled by changing the electrolyte composition. Along with the different phase compositions, a number of different morphologies including nanowires, nanoparticles, nanofibers as well as highly open and dense structures are obtained by varying the acidity of the electrolyte. The effect of morphology and chemical composition on the catalytic activity towards water oxidation is investigated. The film composed of Mn₃O₄ shows low catalytic activities, while the films composed of birnessite‐like manganese oxide phase and Mn₂O₃ exhibit high catalytic activities for water oxidation. The catalytic activities are also affected by the surface morphology, i.e., a higher surface area and more open structure shows a higher catalytic activity. High rates of oxygen production are observed from MnO_x films prepared in a neutral electrolyte.     

Nanoporous PtAg and PtCu alloys with hollow ligaments for enhanced electrocatalysis and glucose biosensing

Nanoporous silver (NPS) and copper (NPC) obtained by dealloying AgAl and CuAl alloys, respectively, were used as both three-dimensional templates and reducing agents for the fabrication of nanoporous PtAg (NPS-Pt) and PtCu (NPC-Pt) alloys with hollow ligaments by a simple galvanic replacement reaction with H(2)PtCl(6). Electron microscopy and X-ray diffraction characterizations demonstrate that NPS and NPC with similar ligament sizes (30-50 nm) have different effects on the formed hollow nanostructures. For NPS-Pt, the shell of the hollow ligament is seamless. However, the shell of NPC-Pt is comprised of small pores and alloy nanoparticles with a size of ～3 nm. The as-prepared NPS-Pt and NPC-Pt exhibit remarkably improved electrocatalytic activities towards the oxidation of ethanol and H(2)O(2) compared with state-of-the-art Pt/C catalyst, and can be used for sensitive electrochemical sensing applications. The hierarchical nanoporous structure also provides a good microenvironment for enzymes. After immobilization of glucose oxidase (GOx), the enzyme modified nanoporous electrode can sensitively detect glucose in a wide linear range (0.6-20 mM).     

A Comprehensive Review on Controlling Surface Composition of Pt‐Based Bimetallic Electrocatalysts

With increasing energy demands worldwide, significant efforts have been made to develop superior electrocatalysts for efficient energy conversion systems. Among all the electrocatalysts exploited, Pt‐based bimetallic nanomaterials stand out by virtue of their high catalytic activity and relatively low cost due to the introduction of a nonprecious metal component. It should be noted that electrocatalytic reactions only take place on the surface of catalysts, so investigations of the surface composition of Pt‐based bimetallic nanomaterials are necessary for practical electrocatalysts. In this review, recent studies on controlling the surface composition of Pt‐based bimetallic catalysts for the oxygen reduction reaction, formic acid electrooxidation, and ethanol electrooxidation are summarized. The controlling strategies, including the chemical method and the electrochemical method, are discussed. The impacts of surface composition compositions on the electrocatalytic performance are also discussed. Finally, the challenges and future directions for controlling the surface composition of Pt‐based bimetallic nanomaterials are addressed.     

Engineering Multimetallic Aerogels for pH‐Universal HER and ORR Electrocatalysis

The advent of noble metal aerogels (NMAs), that feature the high catalytic activity of noble metals and unique structural attributes of aerogels, has stimulated research on a new class of outstanding electrocatalysts. However, limited by the available compositions, the explored electrocatalytic reactions on NMAs are highly restricted and certain important electrochemical processes have not been investigated. Here, an effective gelation approach is demonstrated by using a strong salting‐out agent (i.e., NH₄F), thereby expanding the composition of NMAs to various multimetallic systems and providing a platform to investigate composition‐dependent electrocatalytic performance of NMAs. Combining structural features of aerogels and optimized chemical compositions, the Au–Pt and Au–Rh aerogel catalysts manifest remarkable pH‐universal (pH = 0–14) performance surpassing commercial Pt/C and many other nanoparticle (NP)‐based catalysts in the electrocatalytic oxygen reduction reaction, hydrogen evolution reaction, and water splitting, displaying enormous potential for the electrochemical hydrogen production, fuel cells, etc.     

Highly Efficient Oxygen Reduction Reaction Activity of Graphitic Tube Encapsulating Nitrided CoxFey Alloy

Nonprecious metals are promising catalysts to avoid the sluggish oxygen reduction reaction (ORR) in next‐generation regenerative fuel cells or metal–air batteries. Therefore, development of nonprecious metal catalysts for ORR is highly desirable. Herein, precise tuning of the atomic ratio of Fe and Co encapsulated in melamine‐derived nitrogen‐rich graphitic tube (NGT) is reported. The Co_1.08Fe_3.34 hybrid with metal? nitrogen bonds ( 1 : Co_1.08Fe_3.34@NGT) shows remarkable ORR catalytic activities (80 mV higher in onset potential and 50 mV higher in half‐wave potential than those of state‐of‐the‐art commercial Pt/C catalysts), high current density, and stability. In acidic solution, 1 also shows compatible performance to commercial Pt/C in terms of ORR activity, current density, stability, and methanol tolerance. The high ORR activity is ascribed to the co‐existence of Fe? N, Co? N, and sufficient metallic FeCo alloys which favor faster electron movement and better adsorption of oxygen molecules on the catalyst surface. In the alkaline anion exchange membrane fuel cell setup, this cell delivers the power density of 117 mW cm^?2, demonstrating its potential use for energy conversion and storage applications.     

Ruthenium‐Based Single‐Atom Alloy with High Electrocatalytic Activity for Hydrogen Evolution

Highly efficient and stable catalysts for the hydrogen evolution reaction, especially in alkaline conditions are crucial for the practical demands of electrochemical water splitting. Here, the synthesis of a novel RuAu single‐atom alloy (SAA) by laser ablation in liquid is reported. The SAA exhibits a high stability and a low overpotential, 24 mV@10 mA cm^?2, which is much lower than that of a Pt/C catalyst (46 mV) in alkaline media. Moreover, the turnover frequency of RuAu SAA is three times that of Pt/C catalyst. Density functional theory computation indicates the excellent catalytic activity of RuAu SAAs originates from the relay catalysis of Ru and Au active sites. This work opens a new avenue toward high‐performance SAAs via fast quenching of immiscible metals.     

Surface‐Modified Porous Carbon Nitride Composites as Highly Efficient Electrocatalyst for Zn‐Air Batteries

Porous carbon nitride (PCN) composites are fabricated using a top‐down strategy, followed by additions of graphene and CoS_x nanoparticles. This subsequently enhances conductivity and catalytic activity of PCN (abbreviated as CoS_x@PCN/rGO) and is achieved by one‐step sulfuration of PCN/graphene oxides (GO) composite materials. As a result, the as‐prepared CoS_x@PCN/rGO catalysts display excellent activity and stability toward both oxygen evolution and reduction reactions, surpassing electrocatalytic performance shown by state‐of‐the‐art Pt, RuO₂ and other carbon nitrides. Remarkably, the CoS_x@PCN/rGO bifunctional activity allows for applications in zinc‐air batteries, which show better rechargeability than Pt/C. The enhanced catalytic performance of CoS_x@PCN/rGO can primarily be attributed to the highly porous morphology and sufficiently exposed active sites that are favorable for electrocatalytic reactions.     

Spontaneous Growth of 3D Framework Carbon from Sodium Citrate for High Energy‐ and Power‐Density and Long‐Life Sodium‐Ion Hybrid Capacitors

Carbon sheets with 3D architectures, large graphitic interlayer spacing, and high electrical conductivity are highly expected to be an ideal anode material for sodium‐ion hybrid capacitors (SIHCs). Pursuing a simple synthesis methodology and advancing it from the laboratory to industry is of great importance. In this study, a new approach is presented to prepare 3D framework carbon (3DFC) with the above integrated advantages by a direct calcination of sodium citrate without aid of any additional carbon source, template, or catalyst. The first‐principle calculations verify that the large interlayer spacing and the curvature structure of 3DFC facilitate the sodium ion insertion/extraction. As a consequence, the optimal 3DFC sample exhibits high reversible capacity as well as excellent rate and cycling performance. On this basis, a dual‐carbon SIHC is fabricated by employing 3DFC as battery‐type anode and 3DFC‐derived nanoporous carbon as capacitor‐type cathode. It is able to deliver high energy‐ and power‐density feature as well as outstanding long‐term cycling stability in the potential range of 0–4.0 V. This study may open an avenue for developing high‐performance carbon electrode materials and pushes the practical applications of SIHCs a decisive step forward.     

High‐Temperature Atomic Mixing toward Well‐Dispersed Bimetallic Electrocatalysts

Supported bimetallic alloy nanoparticles are of great interest in various catalytic applications due to the synergistic effects between different metals for improved catalytic performance. However, it still remains a challenge to efficiently synthesize atomically mixed alloy nanoparticles with uniform dispersion onto a desired substrate. Here, in situ, rapid synthesis of atomically mixed bimetallic nanoparticles well‐dispersed on a conductive carbon network via a 1 s high‐temperature pulse (HTP, ≈1550 K, duration 1 s, the rate of 10⁴ K s^?1) is reported. The high temperature facilitates the total (atomic) mixing of different metals, while the rapid quenching ensures the uniform dispersion of nanoparticles with fine features such as twin boundaries and stacking faults, which are potentially beneficial to their catalytic performance. By varying the ratio of the precursor salts and parameters in the HTP process, the composition, size, and morphology of the resultant nanoparticles can easily be tuned. Moreover, the synthesized bimetallic (PdNi) nanoparticles demonstrate excellent electrocatalytic performance for the hydrogen evolution reaction and hydrogen peroxide electrooxidation. This work provides a general strategy for a facile and rapid synthesis of bimetallic nanoparticles directly from their salts for a range of emerging applications.     

Effect of temperature,Si/Al and metal loading on the positioning of Pt atoms in MOR-type zeolites

Metropolis Monte Carlo (MMC) and molecular dynamics (MD) simulations were performed to study the feasibility of synthesising Pt nanowires inside the pores of zeolites with the MOR framework, such as mordenite. Results show that the temperature, the silicon to aluminium ratio (Si/Al) of the zeolite and the Pt metal loading have an important combined effect on the positioning of Pt atoms inside the framework. MMC simulations indicate that low Si/Al and high metal loadings promote the positioning of Pt atoms inside the main pore channels, which are the places where metal nanowires could be formed. On the other hand, high Si/Al and low metal loadings favour the positioning of Pt atoms in the side pockets of the MOR structure. For Pt loadings of 5% (mol/mol), the guest metal atoms were positioned mainly in the main pore channels for all conditions studied. MD simulation results are in agreement with MMC simulations, showing that when Si/Al = ∞, the trend of single Pt atoms is to move towards the side pockets of the MOR framework, while for Si/Al = 5, the Pt atoms remain in the main pore channel of the structure. Temperature had the effect of increasing the mobility of Pt atoms through the MOR framework.     

Pt‐Ir‐Pd Trimetallic Nanocages as a Dual Catalyst for Efficient Oxygen Reduction and Evolution Reactions in Acidic Media

The development of dual catalysts with high efficiency toward oxygen reduction and evolution reactions (ORR and OER) in acidic media is a significant challenge. Here an active and durable dual catalyst based upon cubic Pt₃₉Ir₁₀Pd₁₁ nanocages with an average edge length of 12.3 nm, porous walls as thin as 1.0 nm, and well‐defined {100} facets is reported. The trimetallic nanocages perform better than all the reported dual catalysts in acidic media, with a low ORR‐OER overpotential gap of only 704 mV at a Pt‐Ir‐Pd loading of 16.8 µg_Pt+Ir+Pd cm^?2_geo. For ORR at 0.9 V, when benchmarked against the commercial Pt/C and Pt‐Pd nanocages, the trimetallic nanocages exhibit an enhanced mass activity of 0.52 A mg^?1_Pt+Ir+Pd (about four and two times as high as those of the Pt/C and Pt‐Pd nanocages) and much improved durability. For OER, the trimetallic nanocages show a remarkable mass activity of 0.20 A mg^?1_Pt+Ir at 1.53 V, which is 16.7 and 4.3 fold relative to those of the Pt/C and Pt‐Pd nanocages, respectively. These improvements can be ascribed to the highly open structure of the nanocages, and the possible electronic coupling between Ir and Pt atoms in the lattice.     

Mesoporous Decoration of Freestanding Palladium Nanotube Arrays Boosts the Electrocatalysis Capabilities toward Formic Acid and Formate Oxidation

Fabricating high‐performance electrocatalysts is the most critical step in commercializing direct formic acid or formate fuel cells. In this work, a dual‐template electrodeposition method is used to create freestanding mesoporosity decorated palladium nanotube arrays (P‐PdNTA) as a bifunctional electrocatalyst toward formic acid and formate oxidation (FAO/FOR). The phytantriol‐based soft template modifies the superficial chemistry of aluminum anodic oxide inner surfaces, thereby facilitating the regulated electrodeposition of highly stable palladium nanotubes. The sacrifice of the soft template generates substantial mesoporosity on the nanotubes, resulting in a 189% increase in the electrochemically active surface area with respect to the mesopore‐free PdNTA baseline. In addition, the soft template significantly increases the density of catalytically active sites per unit area via perturbation on routine nanotube growth, as evidenced by the doubled areal catalytic activity of P‐PdNTA versus PdNTA. Remarkably, the P‐PdNTA delivered gravimetric catalytic currents of 3.65 and 3.87 A mg^?1 for FAO and FOR, which are 8.5 and 6.5 times higher, respectively, than those of commercial Pt/C. These values are among the most favorable reported and benefit from the unique synergy of fast substance transport, large electrochemical active surface area and high areal population of catalytically active sites.     

In Situ Exfoliating and Generating Active Sites on Graphene Nanosheets Strongly Coupled with Carbon Fiber toward Self‐Standing Bifunctional Cathode for Rechargeable Zn–Air Batteries

The self‐standing electrode nanomaterials with highly effective bifunctional electrocatalysis for oxygen reduction and evolution reactions (ORR/OER) are important for practical applications in metal–air batteries. Herein, a defect‐enriched and pyridinic‐N (PN) dominated bifunctional electrocatalyst with novel core–shell architecture (DN‐CP@G) is successfully fabricated by in situ exfoliating graphene from carbon paper followed by high temperature ammonia treatment. Benefitting from its strongly coupled core–shell structure, abundant defective sites and high‐content PN dopants, the DN‐CP@G displays an excellent electrocatalytic (ORR and OER) activity and stability in alkaline media, which are comparable to commercial Pt/C and Ir/C catalysts. The experiment, and theoretical calculations demonstrate that the electrocatalytic activities of carbon materials strongly depend on their defective sites and PN dopants. By directly using DN‐CP@G as a self‐standing electrode, the assembled zinc–air battery demonstrates a high discharge performance and outstanding long‐term cycle stability with at least 250 cycles, which is much superior to the mixed Pt/C and Ir/C electrodes. Remarkably, the DN‐CP@G based all‐solid‐state battery also reveals a good discharge and cycle performance. A facile and cost‐efficient approach to prepare highly effective bifunctional self‐standing electrode is provided by in situ generation of active sites on carbon support for metal–air batteries.     

Highly sensitive and selective uric acid biosensor based on RF sputtered NiO thin film

Present study highlights the importance of RF sputtered NiO thin film deposited on platinum coated glass substrate (NiO/Pt/Ti/glass) as a potential matrix for the realization of highly sensitive and selective uric acid biosensor. Uricase has been immobilized successfully onto the surface of NiO matrix by physical adsorption technique. The prepared bioelectrode (uricase/NiO/Pt/Ti/glass) is utilized for sensing uric acid using the cyclic voltammetry and UV visible spectroscopy techniques. The bioelectrode is found to exhibit highly efficient sensing response characteristics with high sensitivity of 1278.48 μA/mM; good linearity of 0.05-1.0 mM, and very low Michaelis-Menten constant (k(m)) of 0.17 mM indicating high affinity of uricase towards the analyte. The enhanced response is due to the development of NiO matrix with good electron transport property and nanoporous morphology for effective loading of enzyme with preferred orientation.     

Engineering Multifunctional Collaborative Catalytic Interface Enabling Efficient Hydrogen Evolution in All pH Range and Seawater

Developing electrocatalysts with high compatibility to the reaction systems with complicated chemical properties represents an important frontier of catalyst design. Herein, a strategy by engineering a multifunctional collaborative catalytic interface to propel the hydrogen evolution reaction (HER) in the full pH range and seawater is reported. Collaborative catalytic interfaces among MXene, bimetallic carbide, and hybridized carbon are demonstrated to afford overall enhancement in electrical conductivity, exposure of reactive sites, water dissociation kinetics, H⁺/water adsorption, and intermediate H binding capability, which satisfy highly variable chemical environment for HER under different pH conditions. Therefore, the HER performance of resultant electrocatalysts can compete with commercial Pt/C in 0.5 m H₂SO₄ or 1.0 m KOH but outperform it under pH 2.2–11.2. They also show exceptional performance for HER in natural seawater with stringent requirements in catalytic activity and stability, exhibiting the best combination of Pt‐like activity, long durability (225 h, 64 times that of Pt/C), and 98% Faradaic efficiency, comparable with commercial Pt/C and the best documented electrocatalysts by far. This work may shed fresh light into the design of effective electrocatalytic interface for regulating the energy chemistry over wide operation conditions, and also inspires the exploration of hydrogen energy utilization technologies and beyond.     

Boosting the Performance of WO3/n‐Si Heterostructures for Photoelectrochemical Water Splitting: from the Role of Si to Interface Engineering

Metal oxide/Si heterostructures make up an exciting design route to high‐performance electrodes for photoelectrochemical (PEC) water splitting. By monochromatic light sources, contributions of the individual layers in WO₃/n‐Si heterostructures are untangled. It shows that band bending near the WO₃/n‐Si interface is instrumental in charge separation and transport, and in generating a photovoltage that drives the PEC process. A thin metal layer inserted at the WO₃/n‐Si interface helps in establishing the relation among the band bending depth, the photovoltage, and the PEC activity. This discovery breaks with the dominant Z‐scheme design idea, which focuses on increasing the conductivity of an interface layer to facilitate charge transport, but ignores the potential profile around the interface. Based on the analysis, a high‐work‐function metal is predicted to provide the best interface layer in WO₃/n‐Si heterojunctions. Indeed, the fabricated WO₃/Pt/n‐Si photoelectrodes exhibit a 2 times higher photocurrent density at 1.23 V versus reversible hydrogen electrode (RHE) and a 10 times enhancement at 1.6 V versus RHE compared to WO₃/n‐Si. Here, it is essential that the native SiO₂ layer at the interface between Si and the metal is kept in order to prevent Fermi level pinning in the Schottky contact between the Si and the metal.     

Free‐Standing 3D Nanoporous Duct‐Like and Hierarchical Nanoporous Graphene Films for Micron‐Level Flexible Solid‐State Asymmetric Supercapacitors

High energy density and power density within a limited volume of flexible solid‐state supercapacitors are highly desirable for practical applications. Here, free‐standing high‐quality 3D nanoporous duct‐like graphene (3D‐DG) films are fabricated with high flexibility and robustness as the backbones to deposit flower‐like MnO₂ nanosheets (3D‐DG@MnO₂). The 3D‐DG is the ideal support for the deposition of large amount of active materials because of its large surface area, appropriate pore structure, and negligible volume compared with other kinds of carbon backbones. Moreover, the 3D‐DG preserve the distinctive 2D coherent electronic properties of graphene, in which charge carriers move rapidly with a small resistance through the high‐quality and continuous chemical vapor deposition‐grown graphene building blocks, which results in a high rate performance. Marvelously, ultrathin (≈50 μm) flexible solid‐state asymmetric supercapacitors (ASCs) using 3D‐DG@MnO₂ as the positive electrode and 3D hierarchical nanoporous graphene films as the negative electrode display ultrahigh volumetric energy density (28.2 mW h cm^?3) and power density (55.7 W cm^?3) at 2.0 V. Furthermore, as‐prepared ASCs show high cycle stability clearly demonstrating their broad applications as power supplies in wearable electronic devices.