Boosting activity and selectivity of glycerol oxidation over platinum–palladium–silver electrocatalysts via surface engineering

A series of platinum–palladium–silver nanoparticles with tunable structures were synthesized for glycerol electro-oxidation in both alkaline and acidic solutions. Electrochemical results indicate that the catalysts show superior activity in alkaline solutions relative to acidic solutions. In alkaline solutions, the peak current densities of ammonia-etched samples are approximately twice those of saturated-NaCl-etched samples. Ammonia-etched platinum–palladium–silver (PtPd@Ag-NH3) exhibits a peak current density of 9.16 mA cm−2, which is 18.7 and 10 times those of the Pt/C and Pd/C, respectively. The product distribution was analyzed by high performance liquid chromatography. Seven products including oxalic acid, tartronic acid, glyoxylic acid, glyceric acid (GLA), glyceraldehyde (GALD), glycolic acid, and dihydroxyacetone (DHA) were detected. The NH3·H2O etched samples tend to generate more GALD, while the NaCl etched samples have a great potential to produce DHA. The addition of Pd atoms can facilitate glycerol oxidation pathway towards the direction of GALD generation. The Pt@Ag-NaCl possesses the largest DHA selectivity of 79.09% at 1.3 V, while the Pt@Ag-NH3 exhibits the largest GLA selectivity of 45.01% at 0.5 V. The PtPd@Ag-NH3 exhibits the largest C3/C2 ratio of 17.45. The selectivity and product distribution of glycerol electro-oxidation can be tuned by engineering the surface atoms of the as-synthesized catalysts

Exceptional Performance of Hierarchical Ni-Fe (hydr)oxide@NiCu Electrocatalysts for Water Splitting

Developing low‐cost bifunctional electrocatalysts with superior activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is of great importance for the widespread application of the water splitting technique. In this work, using earth‐abundant transition metals (i.e., nickel, iron, and copper), 3D hierarchical nanoarchitectures, consisting of ultrathin Ni–Fe layered‐double‐hydroxide (Ni–Fe LDH) nanosheets or porous Ni–Fe oxides (NiFeOx) assembled to a metallic NiCu alloy, are delicately constructed. In alkaline solution, the as‐prepared Ni–Fe LDH@NiCu possesses outstanding OER activity, achieving a current density of 10 mA cm−2 at an overpotential of 218 mV, which is smaller than that of RuO2 catalyst (249 mV). In contrast, the resulting NiFeOx@NiCu exhibits better HER activity, yielding a current density of 10 mA cm−2 at an overpotential of 66 mV, which is slightly higher than that of Pt catalyst (53 mV) but superior to all other transition metal (hydr)oxide‐based electrocatalysts. The remarkable activity of the Ni–Fe LDH@NiCu and NiFeOx@NiCu is further demonstrated by a 1.5 V solar‐panel‐powered electrolyzer, resulting in current densities of 10 and 50 mA cm−2 at overpotentials of 293 and 506 mV, respectively. Such performance renders the as‐prepared materials as the best bifunctional electrocatalysts so far

A Tightly Coupled Bi-Level Coordination Framework for CAVs at Road Intersections

Since the traffic administration at road intersections determines the capacity bottleneck of modern transportation systems, intelligent cooperative coordination for connected autonomous vehicles (CAVs) has shown to be an effective solution. In this paper, we try to formulate a Bi-Level CAV intersection coordination framework, where coordinators from High and Low levels are tightly coupled. In the High-Level coordinator where vehicles from multiple roads are involved, we take various metrics including throughput, safety, fairness and comfort into consideration. Motivated by the time consuming space-time resource allocation framework in [1], we try to give a low complexity solution by transforming the complicated original problem into a sequential linear programming one. Based on the "feasible tunnels" (FT) generated from the High-Level coordinator, we then propose a rapid gradient-based trajectory optimization strategy in the Low-Level planner, to effectively avoid collisions beyond High-level considerations, such as the pedestrian or bicycles. Simulation results and laboratory experiments show that our proposed method outperforms existing strategies. Moreover, the most impressive advantage is that the proposed strategy can plan vehicle trajectory in milliseconds, which is promising in realworld deployments. A detailed description include the coordination framework and experiment demo could be found at the supplement materials, or online at https://youtu.be/MuhjhKfNIOg

Facile synthesis of single atom electrocatalysts via a condensation-carbonization process

The general and cost-effective synthesis of single atom electrocatalysts (SAECs) still remains a great challenge. Herein, we report a general synthetic protocol for the synthesis of SAECs via a simple condensation-carbonization process, in which furfural and cyanamide were condensation polymerized in the presence of polystyrene nanospheres and metal ions, followed by a pyrolysis to N-doped carbon nanosheets (NCNSs) supported SAECs. Six types of SAECs containing platinum, palladium, gold, nickel, cobalt and iron were synthesized to demonstrate the generality of the synthesis protocol. This methodology affords a facile solution to the trade-off between support conductivity and metal loading of SAECs by optimizing the ratio of carbon/nitrogen precursors, i.e., furfural furfuryl and cyanamide. The presence of single metal atoms was confirmed by high-angle annular dark field scanning transmission electron microscopy and X-ray absorption fine structure measurements. The three-dimensional distribution of single platinum atoms was vividly revealed by depth profile analysis in the scanning transmission electron microscope. The resulting SAECs showed excellent performance for glycerol electro-oxidation and water splitting in alkaline solutions. Notably, Pt/NCNs possessed an unprecedent mass-normalized current density of 5.3 A per milligram of platinum, which is 32 times that of the commercial Pt/C catalyst. Density functional theory calculations were conducted to reveal the adsorption behavior of glycerol over the SAECs. Using Ni/NCNSs and Co/NCNSs as anodic and cathodic electrocatalysts, we constructed a solar panel powered electrolytic cell for overall water splitting, leading to an overall energy efficiency of 8.8%, which has been among one of the largest solar-to-hydrogen conversion efficiencies reported in the literature

Hemoglobin-derived Fe-Nx-S species supported by bamboo-shaped carbon nanotubes as efficient electrocatalysts for the oxygen evolution reaction

Herein, we report a facile route to synthesize isolated single iron atoms on nitrogen-sulfur-codoped carbon matrix via a direct pyrolysis process in which hemoglobin, a by-product of the meat industry, was utilized as a precursor for iron, nitrogen and sulfur while bamboo-shaped carbon nanotubes served as a support owing to their excellent conductivity and numerous defects. The resulting metal-nitrogen complexed carbon showed outstanding catalytic performance for the oxygen evolution reaction (OER) in alkaline solutions. At an overpotential of 380 mV, the optimal sample yielded a current density of 83.6 mA cm−2, which is 2.5 times that of benchmark IrO2 (32.8 mA cm−2), rendering it as one of the best OER catalysts reported so far. It also showed negligible activity decay in alkaline solutions during long-term durability tests. Control experiments and X-ray absorption fine structure analyses revealed that Fe-Nx species in the samples are the active sites for OER. Further density functional theory calculations indicated that the presence of sulfur in the carbon matrix modified the electronic structures of active species, thereby leading to the superior activity of the sample

A high-throughput, solvent free method for dispersing metal atoms directly onto supports

Atomically-dispersed metal catalysts (ADMCs) on surfaces have demonstrated high activity and selectivity in many catalytic reactions. However, dispersing and stabilising individual atoms in support materials in an atom/energy-efficient scalable way still presents a significant challenge. Currently, the synthesis of ADMCs involves many steps and further filtration procedures, creating a substantial hurdle to their production at industrial scale. In this work, we develop a new pathway for producing ADMCs in which Pt atoms are stabilised in the nitrogen-interstices of a graphitic carbon nitride (g-C3N4) framework using scalable, solvent-free, one-pot magnetron sputtering deposition. Our approach has the highest reported rate of ADMC production of 4.8 mg h1 and generates no chemical waste. Deposition of only 0.5 weight percent of Pt onto g-C3N4 led to improved hydrogen production by factor of ca. 3333 450 when compared to bare g-C3N4. PL analysis showed that the deposition of Pt atoms onto g-C3N4 suppressed the charge carrier recombination from the photogenerated electron–hole pairs of Pt/g-C3N4 thereby enhance hydrogen evolution. Scanning transmission electron microscope imaging before and after the hydrogen evolution reaction revealed that the Pt atoms stabilised in g-C3N4 have a high stability, with no agglomeration observed. Herein, it is shown that this scalable and clean approach can produce effective ADMCs with no further synthetic steps required, and that they can be readily used for catalytic reactions