Self-Interface in Rh Nanosheets-Supported Tetrahedral Rh Nanocrystals for Promoting Electrocatalytic Oxidation of Ethanol.

Direct ethanol fuel cells hold great promise as a power source. However, their commercialization is limited by anode catalysts with insufficient selectivity toward a complete oxidation of ethanol for a high energy density, as well as sluggish catalytic kinetics and low stability. To optimize the catalytic performance, rationally tuning surface structure or interface structure is highly desired. Herein, a facile route is reported to the synthesis of Rh nanosheets-supported tetrahedral Rh nanocrystals (Rh THs/NSs), which possess self-supporting homogeneous interface between Rh tetrahedrons and Rh nanosheets. Due to full leverage of the structural advantages within the given structure and construction of interfaces, the Rh THs/NSs can serve as highly active electro-catalysts with excellent mass activity and selectivity toward ethanol electro-oxidation. The in situ Fourier transform infrared reflection spectroscopy showed the Rh THs/NSs exhibit the highest C1 pathway selectivity of 23.2%, far exceeding that of Rh nanotetrahedra and Rh nanosheets. Density function theory calculations further demonstrated that self-interface between Rh nanosheets and tetrahedra is beneficial for C-C bond cleavage of ethanol. Meanwhile, the self-supporting of 2D nanosheets greatly enhance the stability of tetrahedra, which improves the catalytic stability.

Highly Selective CO2 Electroreduction to C2+ Products over Cu2O-Decorated 2D Metal-Organic Frameworks with Rich Heterogeneous Interfaces.

The electroreduction of carbon dioxide into high-value-added products is an effective approach to alleviating the energy crisis and pollution issues. However, there are still significant challenges for multicarbon (C2+) product production due to the lack of efficient catalysts with high selectivity. Herein, a Cu-rich electrocatalyst, where Cu2O nanoparticles are decorated on two-dimensional (2D) Cu-BDC metal-organic frameworks (MOFs) with abundant heterogeneous interfaces, is synthesized for highly selective CO2 electroreduction into C2+ products. A high C2+ Faradaic efficiency of 72.1% in an H-type cell and 58.2% in a flow cell are obtained, respectively. The heterogeneous interfaces of Cu2O/Cu-BDC can optimize the adsorption energy of reaction intermediates during CO2 electroreduction. An in situ infrared spectroscopy study indicates that the constructed interfaces can maintain the particular distribution of Cu valence states, where the C-C coupling is promoted to efficiently produce C2+ products owing to the stabilization of *CHO and *COH intermediates.

Oxygen-Bridged Long-Range Dual Sites Boost Ethanol Electrooxidation by Facilitating C-C Bond Cleavage.

Optimizing the interatomic distance of dual sites to realize C-C bond breaking of ethanol is critical for the commercialization of direct ethanol fuel cells. Herein, the concept of holding long-range dual sites is proposed to weaken the reaction barrier of C-C cleavage during the ethanol oxidation reaction (EOR). The obtained long-range Rh-O-Pt dual sites achieve a high current density of 7.43 mA/cm2 toward EOR, which is 13.3 times that of Pt/C, as well as remarkable stability. Electrochemical in situ Fourier transform infrared spectroscopy indicates that long-range Rh-O-Pt dual sites can increase the selectivity of C1 products and suppress the generation of a CO intermediate. Theoretical calculations further disclose that redistribution of the surface-localized electron around Rh-O-Pt can promote direct oxidation of -OH, accelerating C-C bond cleavage. This work provides a promising strategy for designing oxygen-bridged long-range dual sites to tune the activity and selectivity of complicated catalytic reactions.

Perovskite Oxide as A New Platform for Efficient Electrocatalytic Nitrogen Oxidation.

Electrocatalytic nitrogen oxidation reaction (NOR) offers an efficient and sustainable approach for conversion of widespread nitrogen (N2 ) into high-value-added nitrate (NO3 - ) under mild conditions, representing a promising alternative to the traditional approach that involves harsh Haber-Bosch and Ostwald oxidation processes. Unfortunately, due to the weak absorption/activation of N2 and the competitive oxygen evolution reaction, the kinetics of NOR process is extremely sluggish accompanied with low Faradaic efficiencies and NO3 - yield rates. In this work, an oxygen-vacancy-enriched perovskite oxide with nonstoichiometric ratio of strontium and ruthenium (denoted as Sr0.9 RuO3 ) was synthesized and explored as NOR electrocatalyst, which can exhibit a high Faradaic efficiency (38.6 %) with a high NO3 - yield rate (17.9 µmol mg-1 h-1 ). The experimental results show that the amount of oxygen vacancies in Sr0.9 RuO3 is greatly higher than that of SrRuO3 , following the same trend as their NOR performance. Theoretical simulations unravel that the presence of oxygen vacancies in the Sr0.9 RuO3 can render a decreased thermodynamic barrier toward the oxidation of *N2 to *N2 OH at the rate-determining step, leading to its enhanced NOR performance.

Stabilization of Pd0 by Cu Alloying: Theory-Guided Design of Pd3Cu Electrocatalyst for Anodic Methanol Carbonylation.

Electrocatalytic carbonylation of CO and CH3OH to dimethyl carbonate (DMC) on metallic palladium (Pd) electrode offers a promising strategy for C1 valorization at the anode. However, its broader application is limited by the high working potential and the low DMC selectivity accompanied with severe methanol self-oxidation. Herein, our theoretical analysis of the intermediate adsorption interactions on both Pd0 and Pd4+ surfaces revealed that inevitable reconstruction of Pd surface under strongly oxidative potential diminishes its CO adsorption capacity, thus damaging the DMC formation. Further theoretical modeling indicates that doping Pd with Cu not only stabilizes low-valence Pd in oxidative environments but also lowers the overall energy barrier for DMC formation. Guided by this insight, we developed a facile two-step thermal shock method to prepare PdCu alloy electrocatalysts for DMC. Remarkably, the predicted Pd3Cu demonstrated the highest DMC selectivity among existing Pd-based electrocatalysts, reaching a peaked DMC selectivity of 93 % at 1.0 V versus Ag/AgCl electrode. (Quasi) in situ spectra investigations further confirmed the predicted dual role of Cu dopant in promoting Pd-catalyzed DMC formation.

Highly Selective Synthesis of Monoclinic-Phased Platinum-Tellurium Nanotrepang for Direct Formic Acid Oxidation Catalysis.

Designing efficient formic acid oxidation reaction (FAOR) catalysts with remarkable membrane electrode assembly (MEA) performance in a direct formic acid fuel cell (DFAFC) medium is significant yet challenging. Herein, we report that the monoclinic-phased platinum-tellurium nanotrepang (m-PtTe NT) can be adopted as a highly active, selective, and stable FAOR catalyst with a desirable direct reaction pathway. The m-PtTe NT exhibits the high specific and mass activities of 6.78 mA cm-2 and 3.2 A mgPt-1, respectively, which are 35.7/22.9, 2.8/2.6, and 3.9/2.9 times higher than those of commercial Pt/C, rhombohedral-phased Pt2Te3 NT (r-Pt2Te3 NT), and trigonal-phased PtTe2 NT (t-PtTe2 NT), respectively. Simultaneously, the highest reaction tendency for the direct FAOR pathway and the best tolerance to poisonous CO intermediate can also be realized by m-PtTe NT. More importantly, even in a single-cell medium, the m-PtTe NT can display a much higher MEA power density (171.4 mW cm-2) and stability (53.2% voltage loss after 5660 s) than those of commercial Pt/C, demonstrating the great potential in operating DFAFC device. The in-situ Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy jointly demonstrate that the unique nanostructure of m-PtTe NT can effectively optimize dehydrogenation steps and inhibit the CO intermediate adsorption, as well as promote the oxidation of noxious CO intermediate, thus achieving the great improvement of FAOR activity, poisoning tolerance, and stability. Density functional theory calculations further reveal that the direct pathway is the most favorable on m-PtTe NT than r-Pt2Te3 NT and t-PtTe2 NT. The higher activation energy to produce CO and the relatively weaker binding with CO of m-PtTe NT result in the better CO tolerance. This work achieves remarkable FAOR and MEA performances of advanced Pt-based anodic catalysts for DFAFCs via a phase engineering strategy.

Mechanism of Cations Suppressing Proton Diffusion Kinetics for Electrocatalysis.

Proton transfer is crucial for electrocatalysis. Accumulating cations at electrochemical interfaces can alter the proton transfer rate and then tune electrocatalytic performance. However, the mechanism for regulating proton transfer remains ambiguous. Here, we quantify the cation effect on proton diffusion in solution by hydrogen evolution on microelectrodes, revealing the rate can be suppressed by more than 10 times. Different from the prevalent opinions that proton transport is slowed down by modified electric field, we found water structure imposes a more evident effect on kinetics. FTIR test and path integral molecular dynamics simulation indicate that proton prefers to wander within the hydration shell of cations rather than to hop rapidly along water wires. Low connectivity of water networks disrupted by cations corrupts the fast-moving path in bulk water. This study highlights the promising way for regulating proton kinetics via a modified water structure.

High CO-Tolerant Ru-Based Catalysts by Constructing an Oxide Blocking Layer.

CO poisoning of Pt-group metal catalysts is a long-standing problem, particularly for hydrogen oxidation reaction in proton exchange membrane fuel cells. Here, we report a catalyst of Ru oxide-coated Ru supported on TiO2 (Ru@RuO2/TiO2), which can tolerate 1-3% CO, enhanced by about 2 orders of magnitude over the classic PtRu/C catalyst, for hydrogen electrooxidation in a rotating disk electrode test. This catalyst can work stably in 1% CO/H2 for 50 h. About 20% of active sites can survive even in a pure CO environment. The high CO tolerance is not via a traditional bifunctional mechanism, i.e., oxide promoting CO oxidation, but rather via hydrous metal oxide shell blocking CO adsorption. An ab initio molecular dynamics (AIMD) simulation indicates that water confined in grain boundaries of the Ru oxide layer and Ru surface can suppress the diffusion and adsorption of CO. This oxide blocking layer approach opens a promising avenue for the design of high CO-tolerant electrocatalysts for fuel cells.

p-d Orbital Hybridization Induced by a Monodispersed Ga Site on a Pt3 Mn Nanocatalyst Boosts Ethanol Electrooxidation.

Constructing monodispersed metal sites in heterocatalysis is an efficient strategy to boost their catalytic performance. Herein, a new strategy using monodispersed metal sites to tailor Pt-based nanocatalysts is addressed by engineering unconventional p-d orbital hybridization. Thus, monodispersed Ga on Pt3 Mn nanocrystals (Ga-O-Pt3 Mn) with high-indexed facets was constructed for the first time to drive ethanol electrooxidation reaction (EOR). Strikingly, the Ga-O-Pt3 Mn nanocatalyst shows an enhanced EOR performance with achieving 8.41 times of specific activity than that of Pt/C. The electrochemical in situ Fourier transform infrared spectroscopy results and theoretical calculations disclose that the Ga-O-Pt3 Mn nanocatalyst featuring an unconventional p-d orbital hybridization not only promote the C-C bond-breaking and rapid oxidation of -OH of ethanol, but also inhibit the generation of poisonous CO intermediate species. This work discloses a promising strategy to construct a novel nanocatalysts tailored by monodispersed metal site as efficient fuel cell catalysts.

Extraordinary p-d Hybridization Interaction in Heterostructural Pd-PdSe Nanosheets Boosts C-C Bond Cleavage of Ethylene Glycol Electrooxidation.

Advanced electrocatalysts for complete oxidation of ethylene glycol (EG) in direct EG fuel cells are strongly desired owing to the higher energy efficiency. Herein, Pd-PdSe heterostructural nanosheets (Pd-PdSe HNSs) have been successfully fabricated via a one-step approach. These Pd-PdSe HNSs feature unique electronic and geometrical structures, in which unconventional p-d hybridization interactions and tensile strain effect co-exist. Compared with commercial Pd/C and Pd NSs catalysts, Pd-PdSe HNSs display 5.5 (6.6) and 2.5 (2.6) fold enhancement of specific (mass) activity for the EG oxidation reaction (EGOR). Especially, the optimum C1 pathway selectivity of Pd-PdSe HNSs reaches 44.3 %, illustrating the superior C-C bond cleavage ability. Electrochemical in situ FTIR spectroscopy and theoretical calculations demonstrate that the extraordinary p-d hybridization interaction and tensile strain effect could effectively reduce the activation energy of C-C bond breaking and accelerate CO* oxidation, boosting the complete oxidation of EG and improving the catalytic performance.

Effects of ZnO nanoparticles on flocculation and sedimentation of activated sludge in wastewater treatment process.

Despite the behaviors of ZnO nanoparticles (ZnO NPs) in wastewater treatment processes have been widely explored, the impacts of ZnO NPs on the activated sludge's flocculation and sedimentation performances for solid-liquid separation have rarely been involved yet. In this study, ZnO NPs were observed to exert a dose-dependent negative effect on the sludge's flocculation performance but did not significantly impact the sludge' sedimentation behaviors. Furthermore, it was NPs themselves rather than the dissolved Zn2+ who impaired on the sludge flocculation performance because the Zn2+ alone would not compromise the sludge's flocculation efficiency. In addition, the sludge flocculation performance was revealed to be inversely related to the extracellular polymeric substances (EPS) content in the sludge and the direct contacts between ZnO NPs and the cells in the sludge should be the prerequisite to stimulate the secretion of the sludge EPS. The poor sludge flocculation performance could also be caused by the reduced protein/polysaccharide (PN/PS) ratio and the zeta (ζ) potential in the loosely bound (LB-EPS) after the sludge exposure to ZnO NPs. Fourier transform-infrared spectra (FT-IR) and three dimensional - excitation emission fluorescence spectra (3D-EEM) analysis further revealed that the decrease of the tyrosine PN-like substance level in the LB-EPS was probably the key reason for the decreased PN/PS ratio and ζ potential in the LB-EPS, which eventually induced the decline of the sludge flocculation performance under the ZnO NP stress. These results could potentially expand the knowledge on sludge flocculation and sedimentation in the presence of ZnO NPs.

Edge Enrichment of Ultrathin 2D PdPtCu Trimetallic Nanostructures Effectuates Top-Ranked Ethanol Electrooxidation.

Atomic edge sites on two-dimensional (2D) nanomaterials display striking catalytic behavior, whereas edge engineering for 2D metal nanocatalysts remains an insurmountable challenge. Here we advance a one-pot synthesis of ultrathin 2D PdPtCu trimetallic nanosheets and nanorings with escalating low-coordinated edge proportions from 11.74% and 23.11% to 45.85% as cutting-edge ethanol oxidation reaction (EOR) electrocatalysts. This in situ edge enrichment hinges on a competitive surface capping and etching strategy with integrated manipulation of the reaction kinetics. Electrocatalysis tests demystify an edge-relied EOR performance, where the edge-richest 9.0 nm-Pd61Pt22Cu17 nanorings attain an exceptional activity (12.42 A mg-1Pt+Pd, 20.2 times that of commercial Pt/C) with substantially improved durability. Molecularly mechanistic studies certify that the unsaturated edge sites on these 2D catalysts prevail, triggering the C-C bond scission and succeeding CO removal to facilitate a 12-electron-transferring EOR process. This study introduces the "metal-edge-driven" concept and enables the "edge sites on 2D multimetallic nanocatalysts" technique to design versatile heterocatalysts.

A Phosphorus-Doped Ag@Pd Catalyst for Enhanced CC Bond Cleavage during Ethanol Electrooxidation.

Ethanol is preferred to be oxidized into CO2 for the construction of a high-performance direct ethanol fuel cell since this complete ethanol oxidation reaction (EOR) transfers 12 electrons. However, this EOR is sluggish and has the low activity as well as poor selectivity. To promote such a favorable EOR, more exactly the cleavage selectivity of CC bonds in ethanol, phosphorus-doped silver-core-and-Pd-shell catalysts (denoted as Ag@PdP) are designed and synthesized. In the alkaline media, a Ag@Pd2 P0.2 catalyst is superior toward EOR into CO2 . It exhibits seven times higher mass activity and six times higher selectivity than the benchmark Pd/C catalyst. As confirmed by means of density functional theory calculation and in situ Fourier-transform infrared spectroscopy, such high performance stems from an increased adsorption energy of OH radicals on the Pd active sites. Meanwhile, the tensile strain effect of a core-shell structure of this Ag@Pd2 P0.2 catalyst favors the formation of adsorbed CH3 CO intermediate, the key species for the enhanced C-C cleavage into CO2 , instead of acetate. The proposed way to design and synthesize such high-performance EOR catalysts will explore the practical applications of direct alkaline ethanol fuel cells.

Interfacial Structure of Water as a New Descriptor of the Hydrogen Evolution Reaction.

Driven by the persisting poor understanding of the sluggish kinetics of the hydrogen evolution reaction (HER) on Pt in alkaline media, a direct correlation of the interfacial water structure and activity is still yet to be established. Herein, using Pt and Pt-Ni nanoparticles we first demonstrate a strong dependence of the proton donor structure on the HER activity and pH. The structure of the first layer changes from the proton acceptors to the donors with increasing pH. In the base, the reactivity of the interfacial water varied its structure, and the activation energies of water dissociation increased in the sequence: the dangling O-H bonds < the trihedrally coordinated water < the tetrahedrally coordinated water. Moreover, optimizing the adsorption of H and OH intermediates can re-orientate the interfacial water molecules with their H atoms pointing towards the electrode surface, thereby enhancing the kinetics of HER. Our results clarified the dynamic role of the water structure at the electrode-electrolyte interface during HER and the design of highly efficient HER catalysts.

Cooperative Stabilization of the [Pyridinium-CO2-Co] Adduct on a Metal-Organic Layer Enhances Electrocatalytic CO2 Reduction.

Pyridinium has been shown to be a cocatalyst for the electrochemical reduction of CO2 on metal and semiconductor electrodes, but its exact role has been difficult to elucidate. In this work, we create cooperative cobalt-protoporphyrin (CoPP) and pyridine/pyridinium (py/pyH+) catalytic sites on metal-organic layers (MOLs) for an electrocatalytic CO2 reduction reaction (CO2RR). Constructed from [Hf6(µ3-O)4(µ3-OH)4(HCO2)6] secondary building units (SBUs) and terpyridine-based tricarboxylate ligands, the MOL was postsynthetically functionalized with CoPP via carboxylate exchange with formate capping groups. The CoPP group and the pyridinium (pyH+) moiety on the MOL coactivate CO2 by forming the [pyH+--O2C-CoPP] adduct, which enhances the CO2RR and suppresses hydrogen evolution to afford a high CO/H2 selectivity of 11.8. Cooperative stabilization of the [pyH+--O2C-CoPP] intermediate led to a catalytic current density of 1314 mA/mgCo for CO production at -0.86 VRHE, which corresponds to a turnover frequency of 0.4 s-1.

Electrochemical CO2 reduction on Cu and Au electrodes studied using in situ sum frequency generation spectroscopy.

As an important pathway for energy storage and a key reaction in the carbon cycle, the CO2 electrochemical reduction reaction has recently gained significant interest. A variety of catalysts have been used to approach this topic experimentally and theoretically; however, the molecular level insight into the reaction mechanism is lacking due to the complexity of the surface processes and the challenges in probing the intermediate species. In this study, CO2 reduction reactions on polycrystalline Cu and Au electrodes were investigated in 0.1 M CO2-saturated NaHCO3 solution. In situ sum frequency generation (SFG) spectroscopy has been adopted to access the intermediates and products on the metal electrodes. On the Au electrode, only linearly adsorbed CO could be detected, and the reduction produced no hydrocarbon species. On the Cu electrode, C-H stretching vibrations corresponding to surface-adsorbed ethoxy species were observed, but no CO vibrations can be detected with SFG. The results revealed that the CO randomly adsorbed on the Cu surface, and the multiple orientations of the adsorbed species may be the reason for the formation of C-C bonding. These results demonstrate direct molecular level evidence for different reaction pathways on the Cu and Au electrodes.

Synergy between Plasmonic and Electrocatalytic Activation of Methanol Oxidation on Palladium-Silver Alloy Nanotubes.

Localized surface plasmon resonance (LSPR) excitation of noble metal nanoparticles has been shown to accelerate and drive photochemical reactions. Here, LSPR excitation is shown to enhance the electrocatalysis of a fuel-cell-relevant reaction. The electrocatalyst consists of Pdx Ag alloy nanotubes (NTs), which combine the catalytic activity of Pd toward the methanol oxidation reaction (MOR) and the visible-light plasmonic response of Ag. The alloy electrocatalyst exhibits enhanced MOR activity under LSPR excitation with significantly higher current densities and a shift to more positive potentials. The modulation of MOR activity is ascribed primarily to hot holes generated by LSPR excitation of the Pdx Ag NTs.

A Lattice-Oxygen-Involved Reaction Pathway to Boost Urea Oxidation.

The electrocatalytic urea oxidation reaction (UOR) provides more economic electrons than water oxidation for various renewable energy-related systems owing to its lower thermodynamic barriers. However, it is limited by sluggish reaction kinetics, especially by CO2 desorption steps, masking its energetic advantage compared with water oxidation. Now, a lattice-oxygen-involved UOR mechanism on Ni4+ active sites is reported that has significantly faster reaction kinetics than the conventional UOR mechanisms. Combined DFT, 18 O isotope-labeling mass spectrometry, and in situ IR spectroscopy show that lattice oxygen is directly involved in transforming *CO to CO2 and accelerating the UOR rate. The resultant Ni4+ catalyst on a glassy carbon electrode exhibits a high current density (264 mA cm-2 at 1.6 V versus RHE), outperforming the state-of-the-art catalysts, and the turnover frequency of Ni4+ active sites towards UOR is 5 times higher than that of Ni3+ active sites.

Cyclic Penta-Twinned Rhodium Nanobranches as Superior Catalysts for Ethanol Electro-oxidation.

Developing active and durable electro-catalysts toward ethanol oxidation reaction (EOR) with high selectivity toward the C-C bond cleavage is an important issue for the commercialization of direct ethanol fuel cell. Unfortunately, current ethanol oxidation electro-catalysts (e.g., Pt, Pd) still suffer from poor selectivity for direct oxidation of ethanol to CO2, and rapid activity degradation. Here we report a facile route to the synthesis of a new kind of cyclic penta-twinned (CPT) Rh nanostructures that are self-supported nanobranches (NBs) built with 1-dimension CPT nanorods as subunits. Structurally, the as-prepared Rh NBs possess high percentage of open {100} facets with significant CPT-induced lattice strains. With these unique structural characteristics, the as-prepared CPT Rh NBs exhibit outstanding electrocatalytic performance toward EOR in alkaline solution. Most strikingly, the selectivity of complete conversion ethanol to CO2 on the CPT Rh NBs is measured to be as high as 14.5 ± 1.1% at -0.15 V, far exceeding that for single-crystal tetrahedral nanocrystals, icosahedral nanocrystals, and commercial Rh black, as well as majority of reported values for Pt or Pd-based electro-catalysts. By combining with density functional theory calculation, the effects of different structural features of Rh on EOR are definitively elucidated. It was found that the large amount of open Rh (100) facets dominantly contribute to the outstanding activity and exceptionally high selectivity, while the additional tensile strain on (100) planes can further boost the catalytic activity by enhancing the adsorption strength and lowering the reaction barrier of dehydrogenation process of ethanol. As a proof of concept, the present work shows that rationally optimizing surface and electronic structure of electro-catalysts by simultaneously engineering their surface and bulk structures is a promising strategy to promote the performance of electro-catalysts.

Interfacial electronic effects control the reaction selectivity of platinum catalysts.

Tuning the electronic structure of heterogeneous metal catalysts has emerged as an effective strategy to optimize their catalytic activities. By preparing ethylenediamine-coated ultrathin platinum nanowires as a model catalyst, here we demonstrate an interfacial electronic effect induced by simple organic modifications to control the selectivity of metal nanocatalysts during catalytic hydrogenation. This we apply to produce thermodynamically unfavourable but industrially important compounds, with ultrathin platinum nanowires exhibiting an unexpectedly high selectivity for the production of N-hydroxylanilines, through the partial hydrogenation of nitroaromatics. Mechanistic studies reveal that the electron donation from ethylenediamine makes the surface of platinum nanowires highly electron rich. During catalysis, such an interfacial electronic effect makes the catalytic surface favour the adsorption of electron-deficient reactants over electron-rich substrates (that is, N-hydroxylanilines), thus preventing full hydrogenation. More importantly, this interfacial electronic effect, achieved through simple organic modifications, may now be used for the optimization of commercial platinum catalysts.