Highly Efficient Biomass Upgrading by a Ni-Cu Electrocatalyst Featuring Passivation of Water Oxidation Activity.

Electricity-driven organo-oxidations have shown an increasing potential recently. However, oxygen evolution reaction (OER) is the primary competitive reaction, especially under high current densities, which leads to low Faradaic efficiency (FE) of the product and catalyst detachment from the electrode. Here, we report a bimetallic Ni-Cu electrocatalyst supported on Ni foam (Ni-Cu/NF) to passivate the OER process while the oxidation of 5-hydroxymethylfurfural (HMF) is significantly enhanced. A current density of 1000 mA cm-2 can be achieved at 1.50 V vs. reversible hydrogen electrode, and both FE and yield keep close to 100 % over a wide range of potentials. Both experimental results and theoretical calculations reveal that Cu doping impedes the OH* deprotonation to O* and hereby OER process is greatly passivated. Those instructive results provide a new approach to realizing highly efficient biomass upgrading by regulating the OER activity.

Realizing the Excellent HER Performance of Pt3Pb2S2 by d-Orbital Electronic Modulation.

Exploring new excellent electrocatalysts for the hydrogen evolution reaction (HER) is of significance for the development of hydrogen energy. Herein, a ternary chalcogenide (Pt3Pb2S2) is successfully designed and synthesized using layered PtS2 as a matrix. The energy level of the Pt 5d orbital is upshifted to the Fermi surface after replacing S atoms by Pb atoms, which results in the high conductivity of Pt3Pb2S2. In addition, the low-coordinated Pt atoms inserted in the voids of [Pt2Pb2S2] layers have a lower free energy of H* adsorption than do metallic Pt atoms, which endows Pt3Pb2S2 with excellent HER performance. The overpotential and Tafel slope of Pt3Pb2S2 toward HER activity are measured to be 43 mV at 10 mA cm-2 and 43 mV dec-1, respectively. More importantly, Pt3Pb2S2 shows high intrinsic HER catalytic activity and long-term stability. This work provides a promising strategy for designing novel excellent transition-metal chalcogenide electrocatalysts.

Bottom-up evolution of perovskite clusters into high-activity rhodium nanoparticles toward alkaline hydrogen evolution.

Self-reconstruction has been considered an efficient means to prepare efficient electrocatalysts in various energy transformation process for bond activation and breaking. However, developing nano-sized electrocatalysts through complete in-situ reconstruction with improved activity remains challenging. Herein, we report a bottom-up evolution route of electrochemically reducing Cs3Rh2I9 halide-perovskite clusters on N-doped carbon to prepare ultrafine Rh nanoparticles (~2.2 nm) with large lattice spacings and grain boundaries. Various in-situ and ex-situ characterizations including electrochemical quartz crystal microbalance experiments elucidate the Cs and I extraction and Rh reduction during the electrochemical reduction. These Rh nanoparticles from Cs3Rh2I9 clusters show significantly enhanced mass and area activity toward hydrogen evolution reaction in both alkaline and chlor-alkali electrolyte, superior to liquid-reduced Rh nanoparticles as well as bulk Cs3Rh2I9-derived Rh via top-down electro-reduction transformation. Theoretical calculations demonstrate water activation could be boosted on Cs3Rh2I9 clusters-derived Rh nanoparticles enriched with multiply sites, thus smoothing alkaline hydrogen evolution.

Caged-Cation-Induced Lattice Distortion in Bronze TiO2 for Cohering Nanoparticulate Hydrogen Evolution Electrocatalysts.

Defect engineering provides a promising approach for optimizing the trade-off between support structures and active nanoparticles in heterojunction nanostructures, manifesting efficient synergy in advanced catalysis. Herein, a high density of distorted lattices and defects are successfully formed in bronze TiO2 through caging alkali-metal Na cations in open voids (Na-TiO2(B)), which could efficiently cohere nanoparticulate electrocatalysts toward alkaline hydrogen evolution reaction (HER). The RuMo bimetallic nanoparticles could directionally anchor on Na-TiO2(B) with a certain angle of ∼22° due to elimination of the lattice mismatch, thus promoting uniform dispersion and small sizing of supported nanoparticles. Moreover, caging Na ions could significantly enhance the hydrophilicity of the substrate in RuMo/Na-TiO2(B), leading to the strengthening synergy of water dissociation and hydrogen desorption. As expected, this Na-caged nanocomposite catalyst rich with structural perturbations manifests a 6.4-fold turnover frequency (TOF) increase compared to Pt/C. The study provides a paradigm for designing stable nano-heterojunction catalysts with lattice-distorted substrates by caging cations toward advanced electrocatalytic transformations.

A new compound Pt3Bi2S2 with superior performance for the hydrogen evolution reaction.

The exploration of efficient electrocatalysts for the hydrogen evolution reaction (HER) is beneficial to obtain renewable clean energy. Herein, a new parkerite-type compound Pt3Bi2S2 was synthesized, constructed by [PtBi4S2] octahedra. The Bi 6p orbital electrons upshift the Pt 5d band to promote hydrogen adsorption. Moreover, the Bi-Pt orbital hybridization greatly improves the conductivity and accelerates the charge transfer during the electrocatalytic process. Hence, Pt3Bi2S2 exhibits a superior catalytic activity for the HER with a low overpotential of 61 mV (at j = 10 mA cm-2) and a Tafel slope of 51 mV dec-1. In addition, Pt3Bi2S2 has higher stability than commercial Pt/C. This work proposes a promising strategy for designing new excellent HER catalysts.

Intrinsic Electron Localization of Metastable MoS2 Boosts Electrocatalytic Nitrogen Reduction to Ammonia.

The advancement of efficient electrocatalysts toward the nitrogen reduction reaction (NRR) is critical in sustainable ammonia synthesis under ambient pressure and temperature. Manipulating the electronic configuration of electrocatalysts is particularly vital to form metal-nitrogen (MN) bonds during the NRR through regulating the active electronic states of sites. Here, in sharp contrast to stable 2H MoS2 without metal chains, MoMo bonding in metastable polymorphs of MoS2 bulk (zigzag chain in the 1T' phase and diamond chain in the 1T″' phase) is discovered to significantly increase intrinsic electron localization around the metal chains. This can enhance the charge transfer from the adsorbed nitrogen molecule to the metal chains, allowing for boosted NRR kinetics. The electrochemical experiments show that the NH3 yield rate and the faradaic efficiency of the metastable 1T″' MoS2 rich with abundant Mo-Mo bonds are about 9 and 12 times above average than those of 2H MoS2 , correspondingly. Theoretical simulations reveal the high local electron density surrounding the MoMo chains and sites can promote π back-donation, which is beneficial for increasing nitrogen adsorption, strengthening the MN bonds, and reducing the cleavage barrier of the triple NN bond.

A rationally designed 3D interconnected porous tin dioxide cube with reserved space for volume expansion as an advanced anode of lithium-ion batteries.

To work against the volume expansion (∼300%) of SnO2 during lithiation, here a sub-micro sized, interconnected, and porous SnO2 cube with rationally designed reserved space (∼375%) is synthesized via an artful topochemistry route (CaSn(OH)6-CaSnO3-SnO2). Owing to its microstructure, this novel material harvests enhanced lithium-storage performance.

Nanoheterostructures of Partially Oxidized RuNi Alloy as Bifunctional Electrocatalysts for Overall Water Splitting.

Electrocatalytic water splitting, as one of the most promising methods to store renewable energy generated by intermittent sources, such as solar and wind energy, has attracted tremendous attention in recent years. Developing efficient, robust, and green catalysts for the hydrogen and oxygen evolution reactions (HER and OER) is of great interest. This study concerns a facile and green approach for producing RuNi/RuNi oxide nanoheterostructures by controllable partial oxidation of RuNi nanoalloy, which is characterized and confirmed by various techniques, including high-resolution transmission electron microscopy and synchrotron-based X-ray absorption spectroscopy. This nanoheterostructure demonstrates outstanding bifunctional activities for catalyzing the HER and OER with overpotentials that are both among the lowest reported values. In a practical alkali-water-splitting electrolyzer, it also achieves a record-low cell voltage of 1.42 V at 10 mA cm-2 , which is significantly superior to the commercial RuO2 //Pt/C couple and other reported bifunctional water-splitting electrocatalysts. Density functional theory calculations are employed to elaborate the effect of Ni incorporation. This simple catalyst preparation approach is expected to be transferrable to other electrocatalytic reactions.

Three-dimensional interconnected nitrogen-doped mesoporous carbons as active electrode materials for application in electrocatalytic oxygen reduction and supercapacitors.

In this paper, a series of nitrogen-doped mesoporous carbons (NMCs) with three-dimensional (3D) interconnected mesopores have been prepared using flour as carbon source, dicyanamide as nitrogen source and colloidal silica as hard template. The optimized material (NMC-4) prepared with the colloidal silica/flour mass ratio of 4 has a high nitrogen doping level of 5.69 at.% and large specific surface area of 995 m2 g-1 as well as 3D interconnected mesopores (12.9 nm). As the oxygen reduction reaction (ORR) electrocatalyst among various NMCs, NMC-4 exhibits the superior performance and much better stability and methanol crossover with a four-electron dominant reaction pathway compared to commercial 20 wt% Pt/C. Furthermore, as a supercapacitor (SC) electrode material, NMC-4 exhibits a high specific capacitance of 178.5 F g-1 at a current density of 0.5 A g-1 and long cycle life (94.5% capacity retention after 5000 cycles). It also shows a good rate capacity as 76.1% of original specific capacitance remains when the current density increases from 0.5 to 20 A g-1. The high-performance of NMCs results from the synergetic effects of 3D interconnected mesopores, large surface area, and high N-doping level, enabling fast mass transport and electron transfer during the electrochemical process. This work provides a facile and efficient strategy to heteroatom-doped carbons from extensively available biomass, showing great potentials in electrocatalysis, energy storage, and other applications.