Ir-Doped CuPd Single-Crystalline Mesoporous Nanotetrahedrons for Ethylene Glycol Oxidation Electrocatalysis: Enhanced Selective Cleavage of C-C Bond.

The development of highly efficient electrocatalysts for complete oxidation of ethylene glycol (EG) in direct EG fuel cells is of decisive importance to hold higher energy efficiency. Despite some achievements, their progress, especially electrocatalytic selectivity to complete oxidated C1 products, is remarkably slower than expected. In this work, we developed a facile aqueous synthesis of Ir-doped CuPd single-crystalline mesoporous nanotetrahedrons (Ir-CuPd SMTs) as high-performance electrocatalyst for promoting oxidation cleavage of C-C bond in alkaline EG oxidation reaction (EGOR) electrocatalysis. The synthesis relied on precise reduction/co-nucleation and epitaxial growth of Ir, Cu and Pd precursors with cetyltrimethylammonium chloride as the mesopore-forming surfactant and extra Br- as the facet-selective agent under ambient conditions. The products featured concave nanotetrahedron morphology enclosed by well-defined (111) facets, single-crystalline and mesoporous structure radiated from the center, and uniform elemental composition without any phase separation. Ir-CuPd SMTs disclosed remarkably enhanced electrocatalytic activity and excellent stability as well as superior selectivity of C1 products for alkaline EGOR electrocatalysis. Detailed mechanism studies demonstrated that performance improvement came from structural and compositional synergies, which kinetically accelerated transports of electrons/reactants within active sites of penetrated mesopores and facilitated oxidation cleavage of high-energy-barrier C-C bond of EG for desired C1 products. More interestingly, Ir-CuPd SMTs performed well in coupled electrocatalysis of anode EGOR and cathode nitrate reduction, highlighting its high potential as bifunctional electrocatalyst in various applications.

Gradient three-dimensional current collector with lithiophilic nanolayer regulation for efficient lithium metal anode construction.

Metallic lithium (Li) is highly desirable for Li battery anodes due to its unique advantages. However, the growth of Li dendrites poses challenges for commercialization. To address this issue, researchers have proposed various three-dimensional (3D) current collectors. In this study, the selective modification of a 3D Cu foam scaffold with lithiophilic elements was explored to induce controlled Li deposition. The Cu foam was selectively modified with Ag and Sn to create uniform Cu foam (U-Cu) and gradient lithiophilic Cu foam (G-Cu) structures. Density Functional Theory (DFT) calculations revealed that Ag exhibited a stronger binding energy with Li compared to Sn, indicating superior Li induction capabilities. Electrochemical testing demonstrated that the half cell with the G-Cu@Ag electrode exhibited excellent cycling stability, maintaining 550 cycles with an average Coulombic efficiency (CE) of 97.35%. This performance surpassed that of both Cu foam and G-Cu@Sn. The gradient modification of the current collectors improved the utilization of the 3D scaffold and prevented Li accumulation at the top of the scaffold. Overall, the selective modification of the 3D Cu foam scaffold with lithiophilic elements, particularly Ag, offers promising prospects for mitigating Li dendrite growth and enhancing the performance of Li batteries.

High-Power CO2-to-C2 Electroreduction on Ga-Spaced, Square-like Cu Sites.

The electrochemical conversion of CO2 into multicarbon (C2) products on Cu-based catalysts is strongly affected by the surface coverage of adsorbed CO (*CO) intermediates and the subsequent C-C coupling. However, the increased *CO coverage inevitably leads to strong *CO repulsion and a reduced C-C coupling efficiency, thus resulting in suboptimal CO2-to-C2 activity and selectivity, especially at ampere-level electrolysis current densities. Herein, we developed an atomically ordered Cu9Ga4 intermetallic compound consisting of Cu square-like binding sites interspaced by catalytically inert Ga atoms. Compared to Cu(100) previously known with a high C2 selectivity, the Ga-spaced, square-like Cu sites presented an elongated Cu-Cu distance that allowed to reduce *CO repulsion and increased *CO coverage simultaneously, thus endowing more efficient C-C coupling to C2 products than Cu(100) and Cu(111). The Cu9Ga4 catalyst exhibited an outstanding CO2-to-C2 electroreduction, with a peak C2 partial current density of 1207 mA cm-2 and a corresponding Faradaic efficiency of 71%. Moreover, the Cu9Ga4 catalyst demonstrated a high-power (∼200 W) electrolysis capability with excellent electrochemical stability.

Promoting CO2 Electroreduction to Multi-Carbon Products by Hydrophobicity-Induced Electro-Kinetic Retardation.

Advancing the performance of the Cu-catalyzed electrochemical CO2 reduction reaction (CO2 RR) is crucial for its practical applications. Still, the wettable pristine Cu surface often suffers from low exposure to CO2 , reducing the Faradaic efficiencies (FEs) and current densities for multi-carbon (C2+ ) products. Recent studies have proposed that increasing surface availability for CO2 by cation-exchange ionomers can enhance the C2+ product formation rates. However, due to the rapid formation and consumption of *CO, such promotion in reaction kinetics can shorten the residence of *CO whose adsorption determines C2+ selectivity, and thus the resulting C2+ FEs remain low. Herein, we discover that the electro-kinetic retardation caused by the strong hydrophobicity of quaternary ammonium group-functionalized polynorbornene ionomers can greatly prolong the *CO residence on Cu. This unconventional electro-kinetic effect is demonstrated by the increased Tafel slopes and the decreased sensitivity of *CO coverage change to potentials. As a result, the strongly hydrophobic Cu electrodes exhibit C2+ Faradaic efficiencies of ≈90 % at a partial current density of 223 mA cm-2 , more than twice of bare or hydrophilic Cu surfaces.

Facile Synthesis of Hierarchically Porous Ni-N-C for Efficient CO2 Electroreduction to CO.

The reasonable design of atomically dispersed Ni-Nx sites in porous carbon nanostructures is an efficient strategy to enhance the electrochemical CO2 reduction reaction (CO2RR) catalytic activity. In this work, atomically dispersed Ni-Nx sites on hierarchically porous carbon catalysts (HP-Ni-NC) were fabricated by a facile NaCl template-assisted pyrolysis method. The catalysts exhibit a large specific surface area and a hierarchical porous structure, facilitating the exposure of numerous active sites and the mass/electron transport during the CO2RR. Consequently, the CO Faradaic efficiency maintained over 90% in a wide potential window on the optimized HP-Ni-NC-2 catalyst. The CO partial current achieved 15.2 mA cm-2 at -0.9 V (vs reversible hydrogen electrode) in a H-cell. Furthermore, the current density can achieve 250 mA cm-2 at a cell voltage of 3.11 V in a membrane electrode assembly electrolyzer, demonstrating great promise for commercial-scale application. This study presents a facile approach to synthesizing hierarchically porous structure single-atom catalysts with superior catalytic performance toward CO2RR.

Selective Ethylene Glycol Oxidation to Formate on Nickel Selenide with Simultaneous Evolution of Hydrogen.

There is an urgent need for cost-effective strategies to produce hydrogen from renewable net-zero carbon sources using renewable energies. In this context, the electrochemical hydrogen evolution reaction can be boosted by replacing the oxygen evolution reaction with the oxidation of small organic molecules, such as ethylene glycol (EG). EG is a particularly interesting organic liquid with two hydroxyl groups that can be transformed into a variety of C1 and C2 chemicals, depending on the catalyst and reaction conditions. Here, a catalyst is demonstrated for the selective EG oxidation reaction (EGOR) to formate on nickel selenide. The catalyst nanoparticle (NP) morphology and crystallographic phase are tuned to maximize its performance. The optimized NiS electrocatalyst requires just 1.395 V to drive a current density of 50 mA cm-2 in 1 m potassium hydroxide (KOH) and 1 m EG. A combination of in situ electrochemical infrared absorption spectroscopy (IRAS) to monitor the electrocatalytic process and ex situ analysis of the electrolyte composition shows the main EGOR product is formate, with a Faradaic efficiency above 80%. Additionally, C2 chemicals such as glycolate and oxalate are detected and quantified as minor products. Density functional theory (DFT) calculations of the reaction process show the glycol-to-oxalate pathway to be favored via the glycolate formation, where the CC bond is broken and further electro-oxidized to formate.

The Role of Bismuth in Suppressing the CO Poisoning in Alkaline Methanol Electrooxidation: Switching the Reaction from the CO to Formate Pathway.

While tuning the electronic structure of Pt can thermodynamically alleviate CO poisoning in direct methanol fuel cells, the impact of interactions between intermediates on the reaction pathway is seldom studied. Herein, we contrive a PtBi model catalyst and realize a complete inhibition of the CO pathway and concurrent enhancement of the formate pathway in the alkaline methanol electrooxidation. The key role of Bi is enriching OH adsorbates (OHad) on the catalyst surface. The competitive adsorption of CO adsorbates (COad) and OHad at Pt sites, complementing the thermodynamic contribution from alloying Bi with Pt, switches the intermediate from COad to formate that circumvents CO poisoning. Hence, 8% Bi brings an approximately 6-fold increase in activity compared to pure Pt nanoparticles. This notion can be generalized to modify commercially available Pt/C catalysts by a microwave-assisted method, offering opportunities for the design and practical production of CO-tolerance electrocatalysts in an industrial setting.

Pd/Co Catalyst with High Pd Atom Utilization Efficiency for Nitrobenzene Hydrogenation at Room Temperature: Experimental and DFT Studies.

Enhancing catalytic performance as well as reducing catalyst cost are the eternal pursuit for the catalysis community. Herein, a simple and effective palladium-doped cobalt (Pd/Co) catalyst with high Pd atom utilization efficiency was synthesized via galvanic replacement reaction for the selective hydrogenation of nitrobenzene with H2 at room temperature, delivering >99 % yield of aniline with up to 158 times higher catalytic activity than commercial palladium powder. Detailed characterizations and DFT calculations revealed that Co-Pd interaction leads to a decrease in electron density of Pd and the distance between Pd atoms that results in the enhanced catalytic performance. Further experiments indicated that the Pd/Co catalyst serves as a highly efficient, selective, and recyclable catalyst for a range of nitroarene substrates. This work might provide a green and sustainable methodology to design and synthesize highly active catalysts with high utilization efficiency of the noble metals in fundamental and applied research.

Unraveling and tuning the linear correlation between CH4 and C2 production rates in CO2 electroreduction.

Although many catalysts have been reported for the CO2 electroreduction to C1 or C2 chemicals, the insufficient understanding of fundamental correlations among different products still hinders the development of universal catalyst design strategies. Herein, we first discover that the surface *CO coverage is stable over a wide potential range and reveal a linear correlation between the partial current densities of CH4 and C2 products in this potential range, also supported by the theoretical kinetic analysis. Based on the mechanism that *CHO is the common intermediate in the formation of both CH4 (*CHO â†’ CH4) and C2 (*CHO + *CO â†’ C2), we then unravel that this linear correlation is universal and the slope can be varied by tuning the surface *H or *CO coverage to promote the selectivity of CH4 or C2 products, respectively. As proofs-of-concept, using carbon-coated Cu particles, the surface *H coverage can be increased to enhance CH4 production, presenting a high CO2-to-CH4 Faradaic efficiency ( [Formula: see text] ∼52%) and an outstanding CH4 partial current density of -337 mA cm-2. On the other hand, using an Ag-doped Cu catalyst, the CO2RR selectivity is switched to the C2 pathway, with a substantially promoted [Formula: see text] of 79% and a high partial current density of -421 mA cm-2. Our discovery of tuning intermediate coverages suggests a powerful catalyst design strategy for different CO2 electroreduction pathways.

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, COad 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.

Bifunctional effect of Bi(OH)3 on the PdBi surface as interfacial Brønsted base enables ethanol electro-oxidization.

Palladium (Pd) is supposed to be one of the most promising catalytic metals towards ethanol (C2H5OH) oxidation reaction (EOR). However, Pd electrocatalysts easily suffer from the poisoning of the intermediates (especially CO), resulting in the quick decay of EOR catalysis. Herein, inspired by the Brønsted-Lowry acid-base theory, a "attraction-repulsion" concept is proposed to guide the surface structure engineering toward EOR catalysts. Specifically, we induce Bi(OH)3 species as Brønsted base onto PdBi nanoplates to effectively repel the adsorption of CO intermediates. The PdBi-Bi(OH)3 nanoplates show an impressive mass activity of 4.46 A mgPd-1 during the EOR catalysis and keep excellent stability. Both the stability and enhanced performance are attributed by the interfacial Brønsted base Bi(OH)3 which can selectively attract and repel reactants and intermediates, as evidenced from in situ measurements and theoretical views.

Highly Dispersed Mo Sites on Pd Nanosheets Enable Selective Ethanol-to-Acetate Conversion.

The fermentation of biomass allows for the generation of major renewable ethanol biofuel that has high energy density favorable for direct alcohol fuel cells in alkaline media. However, selective conversion of ethanol to either CO2 or acetate remains a great challenge. Especially, the ethanol-to-acetate route usually demonstrates decentoxidation current density relative to the ethanol-to-CO2 route that contains strongly adsorbed poisons. This makes the total oxidation of ethanol to CO2 unnecessary. Here, we present a highly active ethanol oxidation electrocatalyst that was prepared by in situ decorating highly dispersed Mo sites on Pd nanosheets (MoOx/Pd) via a surfactant-free and facile route. We found that ∼2 atom % of Mo on Pd nanosheets increases the current density to 3.8 A mgPd-1, around 2 times more active relative to the undecorated Pd nanosheets, achieving nearly 100% faradic efficiency for the ethanol-to-acetate conversion in an alkaline electrolyte without the generation of detectable CO2, evidenced by in situ electrochemical infrared spectroscopy, nuclear magnetic resonance, and ion chromatography. The selective and CO2-free conversion offers a promising strategy through alcohol fuel cells for contributing comparable current density to power electrical equipment while for selective oxidation of biofuels to useful acetate intermediate for the chemical industry.

Ethanol Electrooxidation on Rhodium-Lead Catalysts in Alkaline Media: High Mass Activity, Long-Term Durability, and Considerable CO2 Selectivity.

Rhodium (Rh)-based catalysts may solve the long-standing inefficient oxidation of ethanol for direct ethanol fuel cells (DEFCs); however, the performance of ethanol oxidation reaction (EOR) on existing Rh-based catalysts are far limited. Herein, the Rh-Pb catalysts are synthesized by building Pb and Pb oxide around Rh nanodomain, which shows highly efficient splitting CC bond and facile further oxidation of as-generated C1 intermediates (COad and CHx fragments). It exhibits an ever-highest EOR peak mass activity of ≈2636 mA mg-1 Rh among Rh-based catalysts in alkaline media. Meanwhile, its anodic current remains ≈50% even after a 4 h durability test at 0.53 V versus RHE. As for the C1-pathway selectivity, in situ infrared adsorption spectral (IRAS) results demonstrate that it could significantly improve the production of CO2 . More directly, the apparent faraday efficiency of EOR C1 pathway is estimated to be as high as 20% (at 0.53 V versus RHE). This Rh-Pb catalyst could hold great promise for developing the commercial DEFCs.

Selective Methanol-to-Formate Electrocatalytic Conversion on Branched Nickel Carbide.

A methanol economy will be favored by the availability of low-cost catalysts able to selectively oxidize methanol to formate. This selective oxidation would allow extraction of the largest part of the fuel energy while concurrently producing a chemical with even higher commercial value than the fuel itself. Herein, we present a highly active methanol electrooxidation catalyst based on abundant elements and with an optimized structure to simultaneously maximize interaction with the electrolyte and mobility of charge carriers. In situ infrared spectroscopy combined with nuclear magnetic resonance spectroscopy showed that branched nickel carbide particles are the first catalyst determined to have nearly 100 % electrochemical conversion of methanol to formate without generating detectable CO2 as a byproduct. Electrochemical kinetics analysis revealed the optimized reaction conditions and the electrode delivered excellent activities. This work provides a straightforward and cost-efficient way for the conversion of organic small molecules and the first direct evidence of a selective formate reaction pathway.

Superior activity of Pd nanoparticles confined in carbon nanotubes for hydrogen production from formic acid decomposition at ambient temperature.

Designing highly efficient and low-cost catalysts is essential toward realizing the practical application of hydrogen generation by formic acid decomposition (FAD) under ambient conditions. Herein, we report the synthesis of a hybrid material of Pd nanoparticles encapsulated within carbon nanotubes (CNTs) (Pd-CNTs-in). Transmission electron microscopy images show that most Pd nanoparticles (mean diameter 4.2 ±â€¯0.8 nm) are located inside the nanotubes. Temperature-programmed reduction studies of H2 reveal that the average reduction temperature of the Pd(II) species adsorbed on the interior wall of the CNTs is 12 °C lower than those adsorbed on the outer walls of the CNT. Moreover, the as-prepared Pd-CNTs-in catalysts show extremely high FAD activity and durability at ambient temperature. The turn over frequency (TOF) value is as high as 1135 h-1 for the initial 10 min and does not decay significantly during the consecutive 3-time recycling studies. X-Ray photoelectron spectroscopy (XPS), surface-enhanced infrared spectroscopy (SEIRAS), and gas chromatography (GC) studies indicate that CNT confinement induced electronic structure modulation of Pd could be the major reason for the enhancement of FAD catalysis on the Pd-CNTs-in surface. This work could provide promising strategies for the fabrication of cost-effective and high-active Pd-based catalysts for formic acid dehydrogenation.

Infrared spectroelectrochemical study of dissociation and oxidation of methanol at a palladium electrode in alkaline solution.

The dissociative adsorption and electrooxidation of CH(3)OH at a Pd electrode in alkaline solution are investigated by using in situ infrared spectroscopy with both internal and external reflection modes. The former (ATR-SEIRAS) has a higher sensitivity of detecting surface species, and the latter (IRAS) can easily detect dissolved species trapped in a thin-layer-structured electrolyte. Real-time ATR-SEIRAS measurement indicates that CH(3)OH dissociates to CO(ad) species at a Pd electrode accompanied by a "dip" at open circuit potential, whereas deuterium-replaced CH(3)OH doesn't, suggesting that the breaking of the C-H bond is the rate-limiting step for the dissociative adsorption of CH(3)OH. Potential-dependent ATR-SEIRAS and IRAS measurements indicate that CH(3)OH is electrooxidized to formate and/or (bi)carbonate, the relative concentrations of which depend on the potential applied. Specifically, at potentials negative of ca. -0.15 V (vs Ag/AgCl), formate is the predominant product and (bi)carbonate (or CO(2) in the thin-layer structure of IRAS) is more favorable at potentials from -0.15 to 0.10 V. Further oxidation of the CO(ad) intermediate species arising from CH(3)OH dissociation is involved in forming (bi)carbonate at potentials above -0.15 V. Although the partial transformation from interfacial formate to (bi)carbonate may be justified, no bridge-bonded formate species can be detected over the potential range under investigation.

Surface-Enhanced Infrared Spectroscopic Study of a CO-Covered Pt Electrode in Room-Temperature Ionic Liquid.

ATR-SEIRAS is extended for the first time to study potential-induced surface and interface structure variation of a CO-covered Pt electrode in a room-temperature ionic liquid of N-butyl-N-methyl-piperidinium bis((trifluoromethyl)sulfonyl)imide (or [Pip14][TNf2]). Owing to a wide effective potential window of [Pip14][TNf2], a gradual conversion from bridged COad (COB) to terminal COad (COL) is observed in response to positively going potentials, suggesting that [Pip14](+) may be involved in a strong electrostatic interaction with the COad. This site conversion enables the ratio of the apparent absorption coefficient of COL to that of COB to be determined. Also, the spectral results reveal the potential-dependent COad frequency variations as well as the potential-induced interfacial ionic reorientation and movement at the Pt/CO/[Pip14][TNf2] interface.

Facile synthesis of Ag@Pd satellites-Fe3O4 core nanocomposites as efficient and reusable hydrogenation catalysts.

Well-dispersed Ag@Pd supported on magnetite nanoparticles have been obtained through a simple colloidal impregnation method. The as-synthesised nanocomposite exhibits greatly enhanced catalytic reactivity and reusability towards 4-nitrophenol hydrogenation.