Promoting H2O2 production via 2-electron oxygen reduction by coordinating partially oxidized Pd with defect carbon.

Electrochemical synthesis of H2O2 through a selective two-electron (2e-) oxygen reduction reaction (ORR) is an attractive alternative to the industrial anthraquinone oxidation method, as it allows decentralized H2O2 production. Herein, we report that the synergistic interaction between partially oxidized palladium (Pdδ+) and oxygen-functionalized carbon can promote 2e- ORR in acidic electrolytes. An electrocatalyst synthesized by solution deposition of amorphous Pdδ+ clusters (Pd3δ+ and Pd4δ+) onto mildly oxidized carbon nanotubes (Pdδ+-OCNT) shows nearly 100% selectivity toward H2O2 and a positive shift of ORR onset potential by ~320 mV compared with the OCNT substrate. A high mass activity (1.946 A mg-1 at 0.45 V) of Pdδ+-OCNT is achieved. Extended X-ray absorption fine structure characterization and density functional theory calculations suggest that the interaction between Pd clusters and the nearby oxygen-containing functional groups is key for the high selectivity and activity for 2e- ORR

Fundamental Understanding and Atomic-Scale Design of Novel Catalysts for Efficient Electrochemical Reactions

The availability of renewable energy sources (solar and wind) provides opportunities to replace many traditional chemical reactions by the electrochemical processes to achieve industrial upgrading, including direct ethanol fuel cells (DEFCs), hydrogen peroxide (H2O2) production, and carbon dioxide (CO2) conversion. However, the rates of many important reactions involved in electrochemical processes are too slow and the selectivity of targeted products also needs to be improved. The key to solve these challenges is to design better electrocatalysts. In this thesis, some strategies to design advanced electrocatalysts are investigated. The first strategy is to control the morphology and surface composition of the Platinum (Pt) nanocube-based electrocatalyst in DEFCs to selectively cleave the C-C bond in ethanol to improve its energy utilization. The (100)-exposed Pt38Ir nanocubes with one-atom-thick Ir-rich skin exhibited unprecedented EOR activity, high CO2 selectivity and long-term stability, due to the promotion of C-C bond cleavage and CO desorption from the catalyst surface. Furthermore, we show that the complete oxidization of ethanol to CO2 was achieved by the Rh single atom on the Pt(100) surface, demonstrating the great potential of the decoration of single atom catalysts on the metallic surface in electrochemical reactions. The second example is to tune the local chemical coordination between atomic catalyst clusters (metal) and their support materials (defect carbons) using a composite approach to achieve the synergistic effect in H2O2 electrochemical production. A catalyst composed of oxidized carbon nanotubes and clusters of three to four partially oxidized palladium (Pd) atoms was prepared, forming a special coordination (Pd-O-C) between carbon material and partially oxidized Pd atoms. This coordination can significantly enhance its H2O2 production rate with > 90% selectivity and shorten the production time. The third strategy is to control the intermediate state of catalyst to promote CO2 reduction. In previous studies, Pd was found to transform into palladium hydride (PdH) during the reaction and the latter was believed to be beneficial for syngas production. Based on this finding, the electrocatalyst was directly designed to partially hydridize Pd nanocubes. In comparison with pure metallic Pd, partial hydridization of Pd structure (PdH0.40) showed an earlier transformation to the key intermediate, leading to enhanced syngas production. As a result, the suitable operation potential range can be extended, resulting in a more flexible working condition for potential industrial applications. Overall, the above three strategies for designing electrocatalysts are explored in this thesis work. The results will provide fundamental understanding and guidance for rational design of highly efficient electrocatalysts for crucial electrochemical reactions, getting one step closer to the industrial applications related to sustainable and green chemical engineering

Fundamental Understanding and Atomic-Scale Design of Novel Catalysts for Efficient Electrochemical Reactions

The availability of renewable energy sources (solar and wind) provides opportunities to replace many traditional chemical reactions by the electrochemical processes to achieve industrial upgrading, including direct ethanol fuel cells (DEFCs), hydrogen peroxide (H2O2) production, and carbon dioxide (CO2) conversion. However, the rates of many important reactions involved in electrochemical processes are too slow and the selectivity of targeted products also needs to be improved. The key to solve these challenges is to design better electrocatalysts. In this thesis, some strategies to design advanced electrocatalysts are investigated. The first strategy is to control the morphology and surface composition of the Platinum (Pt) nanocube-based electrocatalyst in DEFCs to selectively cleave the C-C bond in ethanol to improve its energy utilization. The (100)-exposed Pt38Ir nanocubes with one-atom-thick Ir-rich skin exhibited unprecedented EOR activity, high CO2 selectivity and long-term stability, due to the promotion of C-C bond cleavage and CO desorption from the catalyst surface. Furthermore, we show that the complete oxidization of ethanol to CO2 was achieved by the Rh single atom on the Pt(100) surface, demonstrating the great potential of the decoration of single atom catalysts on the metallic surface in electrochemical reactions. The second example is to tune the local chemical coordination between atomic catalyst clusters (metal) and their support materials (defect carbons) using a composite approach to achieve the synergistic effect in H2O2 electrochemical production. A catalyst composed of oxidized carbon nanotubes and clusters of three to four partially oxidized palladium (Pd) atoms was prepared, forming a special coordination (Pd-O-C) between carbon material and partially oxidized Pd atoms. This coordination can significantly enhance its H2O2 production rate with > 90% selectivity and shorten the production time. The third strategy is to control the intermediate state of catalyst to promote CO2 reduction. In previous studies, Pd was found to transform into palladium hydride (PdH) during the reaction and the latter was believed to be beneficial for syngas production. Based on this finding, the electrocatalyst was directly designed to partially hydridize Pd nanocubes. In comparison with pure metallic Pd, partial hydridization of Pd structure (PdH0.40) showed an earlier transformation to the key intermediate, leading to enhanced syngas production. As a result, the suitable operation potential range can be extended, resulting in a more flexible working condition for potential industrial applications. Overall, the above three strategies for designing electrocatalysts are explored in this thesis work. The results will provide fundamental understanding and guidance for rational design of highly efficient electrocatalysts for crucial electrochemical reactions, getting one step closer to the industrial applications related to sustainable and green chemical engineering

Elucidation and modulation of active sites in holey graphene electrocatalysts for H2O2 production

Abstract Selective electrochemical oxygen reduction (ORR) toward a two‐electron (2e−) pathway is an eco‐friendly alternative method for H2O2 synthesis to replace the energy‐intensive anthraquinone oxidation process. Carbon‐based electrocatalysts (CBEs) show great potential for practical H2O2 synthesis. However, their complex structures make it challenging to determine the nature of active sites and to precisely control them. Herein, we show that precise modulation of the chemistry and structures of holey graphene with edge sites enriched by oxygen‐containing functional groups can facilitate 2e− ORR. These combined functionalities could improve ORR performance under various pH conditions, for example, resulting in an average of 95% H2O2 selectivity, ~97% Faraday efficiency, high productivity of 2360 mol kgcat−1 h−1 in alkaline media. Density functional theory calculations on the oxygen functional groups at the edge sites revealed the most active site for 2e− ORR is a synergy between ether (COC) and carbonyl (CO) functional groups with nearly zero overpotential

Pt–Ni Octahedra as Electrocatalysts for the Ethanol Electro-Oxidation Reaction

Alloying Pt electrocatalysts with late transition metals (e.g., Ni, Co, and Fe) is an effective strategy to lower the catalyst cost and improve their tolerance toward CO in the anode of direct ethanol fuel cells. In this study, shape-controlled octahedral Pt–Ni/C nanocrystals with uniformly exposed (111) facets and an average edge length of 10 nm were synthesized. The octahedral Pt–Ni/C nanocatalyst was at least 4.6 and 7.7 times more active than conventional Pt–Ni/C and commercial Pt/C catalysts, respectively. In situ infrared spectroscopic results showed that the acetic acid/CO₂ absorbance peak intensity on octahedral Pt–Ni/C was 7.6 and 1.4 times higher as compared to commercial Pt/C and conventional Pt–Ni/C, respectively, at 0.75 V. This result suggests that ethanol oxidation on octahedral Pt–Ni produces more acetic acid than on other surfaces. The synergistic electronic and facet effects may explain the superior ethanol oxidation reaction activity of octahedral Pt–Ni/C. Further surface modification with Ru significantly lowered the onset potential for CO₂ production by ∼100 mV and resulted in a higher selectivity on CO₂ as compared to unmodified surface, which further boosted the ethanol utilization efficiency

Overproduction of mycotoxin biosynthetic enzymes triggers Fusarium toxisome-shaped structure formation via endoplasmic reticulum remodeling.

Mycotoxin deoxynivalenol (DON) produced by the Fusarium graminearum complex is highly toxic to animal and human health. During DON synthesis, the endoplasmic reticulum (ER) of F. graminearum is intensively reorganized, from thin reticular structure to thickened spherical and crescent structure, which was referred to as "DON toxisome". However, the underlying mechanism of how the ER is reorganized into toxisome remains unknown. In this study, we discovered that overproduction of ER-localized DON biosynthetic enzyme Tri4 or Tri1, or intrinsic ER-resident membrane proteins FgHmr1 and FgCnx was sufficient to induce toxisome-shaped structure (TSS) formation under non-toxin-inducing conditions. Moreover, heterologous overexpression of Tri1 and Tri4 proteins in non-DON-producing fungi F. oxysporum f. sp. lycopersici and F. fujikuroi also led to TSS formation. In addition, we found that the high osmolarity glycerol (HOG), but not the unfolded protein response (UPR) signaling pathway was involved in the assembly of ER into TSS. By using toxisome as a biomarker, we screened and identified a novel chemical which exhibited high inhibitory activity against toxisome formation and DON biosynthesis, and inhibited Fusarium growth species-specifically. Taken together, this study demonstrated that the essence of ER remodeling into toxisome structure is a response to the overproduction of ER-localized DON biosynthetic enzymes, providing a novel pathway for management of mycotoxin contamination

Palladium–Platinum Core–Shell Electrocatalysts for Oxygen Reduction Reaction Prepared with the Assistance of Citric Acid

Core–shell structure is a promising alternative to solid platinum (Pt) nanoparticles as electrocatalyst for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). A simple method of preparing palladium (Pd)–platinum (Pt) core–shell catalysts (Pd@Pt/C) in a gram-batch was developed with the assistance of citric acid. The Pt shell deposition involves three different pathways: galvanic displacement reaction between Pd atoms and Pt cations, chemical reduction by citric acid, and reduction by negative charges on Pd surfaces. The uniform ultrathin (∼0.4 nm) Pt shell was characterized by in situ X-ray diffraction (XRD) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images combined with electron energy loss spectroscopy (EELS). Compared with state-of-the-art Pt/C, the Pd@Pt/C core–shell catalyst showed 4 times higher Pt mass activity and much better durability upon potential cycling. Furthermore, both the mass activity and durability were comparable to that of Pd@Pt/C synthesized by a Cu-mediated-Pt-displacement method, which is more complicated and difficult for mass production

Promoting H2O2 production via 2-electron oxygen reduction by coordinating partially oxidized Pd with defect carbon.

Electrochemical synthesis of H2O2 through a selective two-electron (2e-) oxygen reduction reaction (ORR) is an attractive alternative to the industrial anthraquinone oxidation method, as it allows decentralized H2O2 production. Herein, we report that the synergistic interaction between partially oxidized palladium (Pdδ+) and oxygen-functionalized carbon can promote 2e- ORR in acidic electrolytes. An electrocatalyst synthesized by solution deposition of amorphous Pdδ+ clusters (Pd3δ+ and Pd4δ+) onto mildly oxidized carbon nanotubes (Pdδ+-OCNT) shows nearly 100% selectivity toward H2O2 and a positive shift of ORR onset potential by ~320 mV compared with the OCNT substrate. A high mass activity (1.946 A mg-1 at 0.45 V) of Pdδ+-OCNT is achieved. Extended X-ray absorption fine structure characterization and density functional theory calculations suggest that the interaction between Pd clusters and the nearby oxygen-containing functional groups is key for the high selectivity and activity for 2e- ORR

Structural Evolution of Sub-10 nm Octahedral Platinum–Nickel Bimetallic Nanocrystals

Octahedral Pt alloy nanocrystals (NCs) have shown excellent activities as electrocatalysts toward oxygen reduction reaction (ORR). As the activity and stability of NCs are highly dependent on their structure and the elemental distribution, it is of great importance to understand the formation mechanism of octahedral NCs and to rationally synthesize shape-controlled alloy catalysts with optimized ORR activity and stability. However, the factors controlling the structural and compositional evolution during the synthesis have not been well understood yet. Here, we systematically investigated the structure and composition evolution pathways of Pt–Ni octahedra synthesized with the assistance of W­(CO)₆ and revealed a unique core–shell structure consisting of a Pt core and a Pt–Ni alloy shell. Below 140 °C, sphere-like pure Pt NCs with the diameter of 3–4 nm first nucleated, followed by the isotropic growth of Pt–Ni alloy on the seeds at temperatures between 170 and 230 °C forming Pt@Pt–Ni core–shell octahedra with {111} facets. Owing to its unique structure, the Pt@Pt–Ni octahedra show an unparalleled stability during potential cycling, that is, no activity drop after 10 000 cycles between 0.6 and 1.0 V. This work proposes the Pt@Pt–Ni octahedra as a high profile electrocatalyst for ORR and reveals the structural and composition evolution pathways of Pt-based bimetallic NCs