Atomic Ordering Engineering of Precious Metal Alloys in Liquid Phase Synthesis.

Atomic ordering of noble metal alloys is an effective strategy for improving catalytic performance, yet the low-temperature synthesis of ordered alloys still faces significant challenges. The low-temperature liquid phase method has enormous potential for the synthesis of alloys; however, the atomic ordering mechanism of this process has not been thoroughly studied. Herein, we investigate the mechanism of the influence of metal precursors, reducing agents, solvents, and mixing modes of reactant regulating strategies on precious metal alloy ordering using this method. These regulating strategies are designed to change the coordination structure of metal complexes, affect the reduction potential of metals, and thus change the reduction order of metals and their arrangement in the alloy products. Notably, the reduction potential differences between metal complexes can be used to predict the ordering of the synthetic products (Pd-Cu, Pd-Cd, Pd-Sn, Pd-Pb, and Pt-Sn). This work provides an excellent platform for investigating atomic arrangement engineering.

Interfacial Accumulation and Stability Enhancement Effects Triggered by Built-in Electric Field of SnO2/LaOCl Nanofibers Boost Carbon Dioxide Electroreduction.

Constructing a built-in interfacial electric field (BIEF) is an effective approach to enhance the electrocatalysts performance, but it has been rarely demonstrated for electrochemical carbon dioxide reduction reaction (CO2RR) to date. Herein, for the first time, SnO2/LaOCl nanofibers (NFs) with BIEF is created by electrospinning, exhibiting a high Faradaic efficiency (FE) of 100% C1 product (CO and HCOOH) at -0.9--1.1 V versus reversible hydrogen electrode (RHE) and a maximum FEHCOOH of 90.1% at -1.2 VRHE in H-cell, superior to the commercial SnO2 nanoparticles (NPs) and LaOCl NFs. SnO2/LaOCl NFs also exhibit outstanding stability, maintaining negligible activity degradation even after 10 h of electrolysis. Moreover, their current density and FEHCOOH are almost 400 mA cm-2 at -2.31 V and 83.4% in flow-cell. The satisfactory CO2RR performance of SnO2/LaOCl NFs with BIEF can be ascribed to tight interface of coupling SnO2 NPs and LaOCl NFs, which can induce charge redistribution, rich active sites, enhanced CO2 adsorption, as well as optimized Gibbs free energy of *OCHO. The work reveals that the BIEF will trigger interfacial accumulation and stability enhancement effects in promoting CO2RR activity and stability of SnO2-based materials, providing a novel approach to develop stable and efficient CO2RR electrocatalysts.

Cation Exchange Strategy to Single-Atom Noble-Metal Doped CuO Nanowire Arrays with Ultralow Overpotential for H2O Splitting.

Single-atom site catalysts (SACs) have aroused enormous attention and brought about new opportunities for many applications. Herein, we report a versatile strategy to rhodium (Rh) SAC by a facile cation exchange reaction. Remarkably, the Rh SAC modified CuO nanowire arrays on copper foam (Rh SAC-CuO NAs/CF) show unprecedented alkaline oxygen evolution reaction (OER) activity with a high current density of 84.5 mA cm-2@1.5 V vs reversible hydrogen electrode (RHE), 9.7 times that of Ir/C/CF. More strikingly, when used as an anode and a cathode for overall water splitting, the Rh SAC-CuO NAs/CF can achieve 10 mA cm-2 at only 1.51 V. Density functional theory calculations reveal that the high OER and HER intrinsic catalytic activities result from moderate adsorption energy of intermediates on Rh SAC. Finally, we demonstrate the general synthesis of different single-atom noble-metal catalysts on CuO NAs (M SAC-CuO NAs/CF, where M = Ru, Ir, Os, and Au).

Multicomponent Pt-Based Zigzag Nanowires as Selectivity Controllers for Selective Hydrogenation Reactions.

The selective hydrogenation of α, ß-unsaturated aldehyde is an extremely important transformation, while developing efficient catalysts with desirable selectivity to highly value-added products is challenging, mainly due to the coexistence of two conjugated unsaturated functional groups. Herein, we report that a series of Pt-based zigzag nanowires (ZNWs) can be adopted as selectivity controllers for α, ß-unsaturated aldehyde hydrogenation, where the excellent unsaturated alcohol (UOL) selectivity (>95%) and high saturated aldehyde (SA) selectivity (>94%) are achieved on PtFe ZNWs and PtFeNi ZNWs+AlCl3, respectively. The excellent UOL selectivity of PtFe ZNWs is attributed to the lower electron density of the surface Pt atoms, while the high SA selectivity of PtFeNi ZNWs+AlCl3 is due to synergy between PtFeNi ZNWs and AlCl3, highlighting the importance of Pt-based NWs with precisely controlled surface and composition for catalysis and beyond.

Promoting the Direct H2 O2 Generation Catalysis by Using Hollow Pd-Sn Intermetallic Nanoparticles.

Although direct hydrogen (H2 ) oxidation to hydrogen peroxide (H2 O2 ) is considered as a promising strategy for direct H2 O2 synthesis, the desirable conversion efficiency remains formidable challenge. Herein, highly active and selective direct H2 oxidation to H2 O2 is achieved by using hollow Pd-Sn intermetallic nanoparticles (NPs) as the catalysts. By tuning the catalytic solvents and catalyst supports, the efficiency of direct H2 oxidation to H2 O2 can be optimized well with the hollow Pd2 Sn NPs/P25 exhibiting H2 O2 selectivity up to 80.7% and productivity of 60.8 mol kgcat-1 h-1 . In situ diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption results confirm the different surface atom arrangements between solid and hollow Pd-Sn NPs. X-ray photoelectron spectra results show that the higher efficiency of Pd2 Sn NPs/P25 is due to its higher content of metallic Pd and higher ratio of Snx+ , which benefit H2 O2 production and selectivity.

Highly Active and Selective Hydrogenation of CO2 to Ethanol by Ordered Pd-Cu Nanoparticles.

Carbon dioxide (CO2) hydrogenation to ethanol (C2H5OH) is considered a promising way for CO2 conversion and utilization, whereas desirable conversion efficiency remains a challenge. Herein, highly active, selective and stable CO2 hydrogenation to C2H5OH was enabled by highly ordered Pd-Cu nanoparticles (NPs). By tuning the composition of the Pd-Cu NPs and catalyst supports, the efficiency of CO2 hydrogenation to C2H5OH was well optimized with Pd2Cu NPs/P25 exhibiting high selectivity to C2H5OH of up to 92.0% and the highest turnover frequency of 359.0 h-1. Diffuse reflectance infrared Fourier transform spectroscopy results revealed the high C2H5OH production and selectivity of Pd2Cu NPs/P25 can be ascribed to boosting *CO (adsorption CO) hydrogenation to *HCO, the rate-determining step for the CO2 hydrogenation to C2H5OH.

Highly Efficient Carbon Dioxide Hydrogenation to Methanol Catalyzed by Zigzag Platinum-Cobalt Nanowires.

Carbon dioxide (CO2 ) hydrogenation is an effective strategy for CO2 utilization, while unsatisfied conversion efficiencies remain great challenges. It is reported herein that zigzag Pt-Co nanowires (NWs) with Pt-rich surfaces and abundant steps/edges can perform as highly active and stable CO2 hydrogenation catalysts. It is found that tuning the Pt/Co ratio of the Pt-Co NWs, solvents, and catalyst supports could well optimize the CO2 hydrogenation to methanol (CH3 OH) with the Pt4 Co NWs/C exhibiting the best performance, outperforming all the previous catalysts. They are also very durable with limited activity decays after six catalytic cycles. The diffuse reflectance infrared Fourier transform spectroscopy result of CO2 adsorption shows that the Pt4 Co NWs/C undergoes the adsorption/activation of CO2 by forming appropriate carboxylate intermediates, and thus enhancing the CH3 OH production.

Amorphous ZnSnOx Hollow Spheres Enable Highly Efficient CO2 Reduction.

Carbon dioxide (CO2) adsorption and electron transport play an important role in CO2 reduction reaction (CO2RR). Herein, we have demonstrated a new class of diverse hollow ZnSnOx (ZSO) through the amorphization of hydroxides to enhance CO2 adsorption and accelerate electron transport. The amorphization is occurred by calcination process, as indicated by Fourier transform infrared spectroscopy and Raman spectra. In particular, the ZnSnOx hollow spheres (ZSO HSs) achieve a high Faradaic efficiency (FE) of HCOOH up to 92.7 % at best, outperforming the commercial ZSO (Comm. ZSO, 85.7 %). ZSO HSs also exhibit durable stability with negligible activity decay after 10 h of successive electrolysis. In-situ attenuated total reflectance infrared absorption spectroscopy further reveals strong adsorption of CO2 and rapid intermediate configuration transformation in amorphous ZSO HSs. This work demonstrates the practical application of ZSO for CO2RR and provides a new insight to create efficient CO2RR electrocatalysts.

Stable and Ordered Body-Centered Cubic PdCu Phase for Highly Selective Hydrogenation.

Phase engineering of nanomaterials plays a crucial role for regulating the catalytic performance. Nevertheless, great challenges still remain for elucidating the structure-selectivity correlation. Herein, this study demonstrates that the body-centered cubic phase of PdCu (bcc-PdCu) can serve as a highly active and selective catalyst for 3-nitrostyrene (NS) hydrogenation under mild conditions. In particular, bcc-PdCu displays a 3-nitro-ethylbenzene (NE) selectivity of 93.8% with a turnover frequency (TOF) value of 4573 h-1 at 30 °C in the presence of H2 . With the assistance of NH3 ∙BH3 , the selectivity of 3-amino-styrene (AS) reaches 94.5% with a TOF value of 13 719 h-1 . Detailed experimental and theoretical calculations reveal that improved NE selectivity is ascribed to the selective adsorption of the CC bond and desorption of NE on bcc-PdCu. Moreover, the presence of NH3 ∙BH3 facilitates the selective hydrogenation of NO2 due to their strong interaction and thus leads to the formation of AS. This work provides an efficient selective catalyst for NS hydrogenation under mild conditions, which may attract immediate interests in the fields of materials, chemistry, and catalysis.

High-Entropy Alloy Aerogels: A New Platform for Carbon Dioxide Reduction.

High-entropy alloy aerogels (HEAAs) combined with the advantages of high-entropy alloys and aerogels are prospective new platforms in catalytic reactions. However, due to the differences in reduction potentials and miscibility behavior of different metals, the realization of HEAAs with a single phase is still a great challenge. Herein, a series of HEAAs is fabricated via the freeze-thaw method as highly active and durable electrocatalysts for the carbon dioxide reduction reaction (CO2 RR). Especially, the PdCuAuAgBiIn HEAAs can achieve Faradaic efficiency (FE) of C1 products almost 100% from -0.7 to -1.1 V versus reversible hydrogen electrode (VRHE ), and a maximum FE for formic acid (FEHCOOH ) of 98.1% at -1.1 VRHE , outperforming PdCuAuAgBiIn high-entropy alloy particles (HEAPs) and Pd metallic aerogels (MAs). Specifically, the current density and FEHCOOH are almost 200 mA cm-2 and 87% in a flow cell. The impressive CO2 RR performance of the PdCuAuAgBiIn HEAAs is attributed to the strong interactions between the different metals and the surface unsaturated sites, which can regulate the electronic structures of different metals and allow the optimal HCOO* intermediate adsorption and desorption onto the catalysts surface to enhance HCOOH production. The work not only provides a facile synthetic strategy to fabricate HEAAs, but also opens the avenue for development of efficient catalysts and beyond.

Selective Ethanol Oxidation Reaction at the Rh-SnO2 Interface.

Direct ethanol fuel cells (DEFCs) are regarded as an attractive power source with high energy density, bio-renewability, and convenient storage and transportation. However, the anodic reaction of DEFCs, that is, the ethanol oxidation reaction (EOR), suffers from poor efficiency due to the low selectivity to CO2 (C1 pathway) and high selectivity to CH3 COOH (C2 pathway). In this study, the selective EOR to CO2 can be achieved at the Rh-SnO2 interface in SnO2 -Rh nanosheets (NSs). The optimized catalyst of 0.2SnO2 -Rh NSs/C exhibits excellent alkaline EOR performance with a mass activity of 213.2 mA mgRh -1 and a Faraday efficiency of 72.8% for the C1 pathway, which are 1.7 and 1.9 times higher than those of Rh NSs/C. Mechanism studies indicate that the strong synergy at the Rh-SnO2 interface significantly promotes the breaking of CC bond of C2 H5 OH to form CO2 , and facilitates oxidation of the poisonous intermediates (* CO and * CH3 ) to suppress the deactivation of the catalyst. This work not only provides a highly selective, active, and stable catalyst for the EOR, but also promotes fundamental research for the design of efficient catalysts via interface modification.

Evolution of PtCu tripod nanocrystals to dendritic triangular nanocrystals and study of the electrochemical performance to alcohol electrooxidation.

In the field of catalysis, the design and construction of nanomaterials is an efficient way to optimize the catalytic activity of catalysts. This study presents the synthesis of PtCu tripod nanocrystals with branching structures and high purity prepared using a simple hydrothermal method. The dendritic PtCu triangular nanocrystals were successfully synthesized by regulating the amount of I- ions to achieve different degrees of branching on PtCu nanocrystals, and the process was systematically studied and analyzed. Meanwhile, dumbbell nanocrystals of PtCu were successfully synthesized through slight adjustments to synthesis conditions. In electrochemical tests, the obtained dendritic PtCu triangular nanocrystals exhibited prominent electrocatalytic activity and long-term stability for ethylene glycol, methanol, and ethanol oxidation reactions due to the unique nanostructures as well as alloyed virtue, and were much better than commercial Pt/C. In addition, this study provides a general strategy for designing novel branched Pt-based nanomaterials with high electrocatalytic performance.

Compensating Electronic Effect Enables Fast Site-to-Site Electron Transfer over Ultrathin RuMn Nanosheet Branches toward Highly Electroactive and Stable Water Splitting.

To improve the electroactivity and stability of electrocatalysts, various modulation strategies have been applied in nanocatalysts. Among different methods, heteroatom doping has been considered as an effective method, which modifies the local bonding environments and the electronic structures. Meanwhile, the design of novel two-dimensional (2D) nanostructures also offers new opportunities for achieving efficient electrocatalysts. In this work, Mn-doped ultrathin Ru nanosheet branches (RuMn NSBs), a newly reported 2D nanostructure, is synthesized. With the ultrathin and naturally abundant edges, the RuMn NSBs have exhibited bifunctionalities of hydrogen evolution reaction and oxygen evolution reaction with high electroactivity and durability in different electrolytes. Experimental characterizations have revealed that RuO bonds are shortened due to Mn doping, which is the key factor that leads to improved electrochemical performances. Density functional theory (DFT) calculations have confirmed that the introduction of Mn enables flexible modulations on the valence states of Ru sites. The inversed redox state evolutions of Ru and Mn sites not only improve the electroactivity for the water splitting but also the long-term stability due to the pinning effect of Ru sites. This work has provided important inspirations for the design of future advanced Ru-based electrocatalysts with high performances and durability.

A Generalized Surface Chalcogenation Strategy for Boosting the Electrochemical N2 Fixation of Metal Nanocrystals.

Electrocatalytic nitrogen reduction reaction (NRR) is a promising process relative to energy-intensive Haber-Bosch process. While conventional electrocatalysts underperform with sluggish paths, achieving dissociation of N2 brings the key challenge for enhancing NRR. This study proposes an effective surface chalcogenation strategy to improve the NRR performance of pristine metal nanocrystals (NCs). Surprisingly, the NH3 yield and Faraday efficiency (FE) (175.6 ± 23.6 mg h-1 g-1 Rh and 13.3 ± 0.4%) of Rh-Se NCs is significantly enhanced by 16 and 15 times, respectively. Detailed investigations show that the superior activity and high FE are attributed to the effect of surface chalcogenation, which not only can decrease the apparent activation energy, but also inhibit the occurrence of the hydrogen evolution reaction (HER) process. Theoretical calculations reveal that the strong interface strain effect within core@shell system induces a critical redox inversion, resulting in a rather low valence state of Rh and Se surface sites. Such strong correlation indicates an efficient electron-transfer minimizing NRR barrier. Significantly, the surface chalcogenation strategy is general, which can extend to create other NRR metal electrocatalysts with enhanced performance. This strategy open a new avenue for future NH3 production for breakthrough in the bottleneck of NRR.

High-efficiency direct methane conversion to oxygenates on a cerium dioxide nanowires supported rhodium single-atom catalyst.

Direct methane conversion (DMC) to high value-added products is of significant importance for the effective utilization of CH4 to combat the energy crisis. However, there are ongoing challenges in DMC associated with the selective C-H activation of CH4. The quest for high-efficiency catalysts for this process is limited by the current drawbacks including poor activity and low selectivity. Here we show a cerium dioxide (CeO2) nanowires supported rhodium (Rh) single-atom (SAs Rh-CeO2 NWs) that can serve as a high-efficiency catalyst for DMC to oxygenates (i.e., CH3OH and CH3OOH) under mild conditions. Compared to Rh/CeO2 nanowires (Rh clusters) prepared by a conventional wet-impregnation method, CeO2 nanowires supported Rh single-atom exhibits 6.5 times higher of the oxygenates yield (1231.7 vs. 189.4 mmol gRh-1 h-1), which largely outperforms that of the reported catalysts in the same class. This work demonstrates a highly efficient DMC process and promotes the research on Rh single-atom catalysts in heterogeneous catalysis.

Se-Incorporation Stabilizes and Activates Metastable MoS2 for Efficient and Cost-Effective Water Gas Shift Reaction.

Although the water gas shift (WGS) reaction has sparked intensive attention for the production of high-purity hydrogen, the design of cost-efficient catalysts with noble metal-like performance still remains a great challenge. Here, we successfully overcome this obstacle by using Se-incorporated MoS2 with a 1T phase. Combining the optimized electronic structure, additional active sites from edge sites, and a sulfur vacancy based on the 1T phase, as well as the high surface ratio from the highly open structure, the optimal MoS1.75Se0.25 exhibits superior activity and stability compared to the conventional 2H-phase MoS2, with poor activity, large sulfur loss, and rapid inactivation. The hydrogen production of MoS1.75Se0.25 is 942 µmol, which is 1.9 times higher than MoS2 (504 µmol) and 2.8 times higher than MoSe2 (337 µmol). Furthermore, due to the lattice stabilization via Se-incorporation, MoS1.75Se0.25 exhibited excellent long-term stability without obvious change in more than 10 reaction rounds. Our results demonstrate a pathway to design efficient and cost-efficient catalysts for WGS.

Universal Strategy for Ultrathin Pt-M (M = Fe, Co, Ni) Nanowires for Efficient Catalytic Hydrogen Generation.

Methanol (CH3OH) reformation with water (H2O) to in situ release hydrogen (H2) is regarded as a hopeful H2 production approach for polymer electrolyte membrane fuel cells, while developing highly efficient CH3OH reformation catalysts still remains a great challenge. Herein, a series of Pt-based ultrafine nanowires (UNWs) with high surface atom ratio are used as highly active and stable catalysts for CH3OH reformation to H2. By tuning Pt3M (M = Fe, Co, Ni), support and the composition of the Pt xFe UNWs, the optimized Pt4Fe UNWs/Al2O3 exhibits excellent catalytic behaviors with the high H2 turnover frequency reaching to 2035.8 h-1, more than 4 times higher than that of Pt UNWs/Al2O3. The reaction mechanism investigated by diffuse reflectance infrared Fourier transform spectroscopy turns out that the production of H2 undergoes the CH3OH decomposition to *CO and gas-shift reaction of *CO with H2O. Combing with the XPS result and the density functional theory calculations, the high CH3OH reformation activity of Pt4Fe UNWs/Al2O3 is attributable to synergism between Pt and Fe, which facilitates H2 desorption and intermediate HCOO* and *COO formations via the reaction between *CO and OH-.

1,2-Dichloroethane Deep Oxidation over Bifunctional Ru/Ce x Al y Catalysts.

Ru/Ce x Al y catalysts were synthesized with impregnation of RuCl3 aqueous solution on Ce x Al y (Al2O3-CeO2) and used in 1,2-dichloroethane (1,2-DCE) oxidation. Characterization by X-ray diffraction, Raman, NH3-temperature-programmed desorption (TPD), CO2-TPD, X-ray photoelectron spectroscopy, and H2-temperature-programmed reduction indicates that CeO2 exists as a form of face-centered cubic fluorite structure, whereas the chemical states and the structure of Ru species are dependent on the Ce content. The reducibility and acidity of catalysts increase with Ce/Ce + Al ratio. However, the latter is promoted only in a Ce/Ce + Al range of 0-0.25 and then decreases quickly. Ru/Ce x Al y catalysts have considerable activity for 1,2-DCE combustion. TOFRu of 1,2-DCE oxidation increases with strong acid, which is ascribed to a synergy of reducibility and acidity. Ru greatly inhibits the chlorination through the decreases in both Cl deposition and CH2=CHCl formation. High stability of Ru/Ce10Al90 maintains at 280 °C for at least 25 h with CO2 selectivity of 99% or higher. In situ Fourier transform infrared spectroscopy indicates that 1,2-DCE dissociates to form ClCH2-CH2O- species, which is an intermediate species for the production of CH3CHO and CH2=CHCl, the former responsible for deep oxidation.