Cross-linked α-Ni(OH)2 nanosheets with a Ni3+-rich structure for accelerating electrochemical oxidation of 5-hydroxymethylfurfural.

Electrochemical oxidation of biomass-based 5-hydroxymethylfurfural (HMF) is an effective approach for achieving the high-value products of 2,5-furandicarboxylic acid (FDCA). However, the restricted formation of high-valence metal active species for electrocatalysts results in a sluggish kinetic process of HMF oxidation reaction (HMFOR). Herein, we fabricated the Ni3+-rich cross-linked α-Ni(OH)2 nanosheets for accelerating the HMFOR through an anion-mediated strategy. It is identified that the Cl- ions with strong penetrability replace a portion of lattice oxygen atoms in α-Ni(OH)2 to form Ni-Cl bonds, contributing to breaking the inherent lattice order and generating a special Ni3+-rich structure. Owing to the promoted adsorption and accelerated oxidation of hydroxyl and aldehyde groups by the affluent Ni3+ active species, the large oxidation current density of 116.5 mA cm-2 and HMFOR kinetic constant of 0.067 min-1 has been achieved at 1.45 V (vs. RHE). By analyzing the oxidation products, the FDCA yield and Faradic efficiency are both higher than 99.25 % and 99.36 % for five successive determinations. Therefore, this work provides an insightful anion-mediated strategy for designing high-performance electrocatalysts for biomass conversion application.

Structural design of FeCo alloy implanted into N,S co-doped carbon nanotubes via self-catalyzed growth for advanced liquid and flexible all-state-state Zn-air battery.

The introduction of transition bimetallic alloys can effectively improve oxygen reduction reaction (ORR) activity. However, the alloy particles are inclined to dissolve under harsher conditions, resulting in a serious decrease in catalytic activity and stability. Herein, an efficient ORR catalyst, FeCo alloy nanoparticles (NPs) encapsulated in N,S co-doped carbon nanotubes (FeCo10-NSCNTs), was developed through a self-catalyzed growth strategy. Due to the delicate structural design, the N,S co-doped structure can effectively improve the ORR performance by modulating the electronic properties and surface polarity of the carbon substrate, and the randomly connected carbon nanotube structure with large specific surface area can further enhance the adsorption and dissociation of gas molecules, accelerating the kinetics of gas participation in the reaction. Carbon-encapsulated FeCo alloys are beneficial for improving catalytic activity and durability. The FeCo10-NSCNTs displayed excellent ORR activity with a half-wave potential of E1/2 = 0.84 V and robust stability of 13 k cycles. More impressively, the assembled liquid-state Zn-air battery (ZAB) with FeCo10-NSCNTs as the air-electrode delivers an output power density of 146.68 mW cm-2 along with excellent operation durability. The assembled all-solid ZAB has good cyclic stability under 0-180° bending conditions. The synthesized N,S co-doping, carbon nanotubes and FeCo alloys provide important guidance for the construction of cheap non-noble metal-carbon hybrid nanomaterials.

Single-Atom Zinc Sites with Synergetic Multiple Coordination Shells for Electrochemical H2 O2 Production.

Precise manipulation of the coordination environment of single-atom catalysts (SACs), particularly the simultaneous engineering of multiple coordination shells, is crucial to maximize their catalytic performance but remains challenging. Herein, we present a general two-step strategy to fabricate a series of hollow carbon-based SACs featuring asymmetric Zn-N2 O2 moieties simultaneously modulated with S atoms in higher coordination shells of Zn centers (n≥2; designated as Zn-N2 O2 -S). Systematic analyses demonstrate that the synergetic effects between the N2 O2 species in the first coordination shell and the S atoms in higher coordination shells lead to robust discrete Zn sites with the optimal electronic structure for selective O2 reduction to H2 O2 . Remarkably, the Zn-N2 O2 moiety with S atoms in the second coordination shell possesses a nearly ideal Gibbs free energy for the key OOH* intermediate, which favors the formation and desorption of OOH* on Zn sites for H2 O2 generation. Consequently, the Zn-N2 O2 -S SAC exhibits impressive electrochemical H2 O2 production performance with high selectivity of 96 %. Even at a high current density of 80 mA cm-2 in the flow cell, it shows a high H2 O2 production rate of 6.924 mol gcat -1 h-1 with an average Faradaic efficiency of 93.1 %, and excellent durability over 65 h.

Supramolecular Self-Assembly Strategy towards Fabricating Mesoporous Nitrogen-Rich Carbon for Efficient Electro-Fenton Degradation of Persistent Organic Pollutants.

The electro-Fenton (EF) process is regarded as an efficient and promising sewage disposal technique for sustainable water environment protection. However, current developments in EF are largely restricted by cathode electrocatalysts. Herein, a supramolecular self-assembly strategy is adopted for synthetization, based on melamine-cyanuric acid (MCA) supramolecular aggregates integrated with carbon fixation using 5-aminosalicylic acid and zinc acetylacetonate hydrate. The prepared carbon materials characterize an ordered lamellar microstructure, high specific surface area (595 m2 g-1), broad mesoporous distribution (4~33 nm) and high N doping (19.62%). Such features result from the intrinsic superiority of hydrogen-bonded MCA supramolecular aggregates via the specific molecular assembly process. Accordingly, noteworthy activity and selectivity of H2O2 production (~190.0 mg L-1 with 2 h) are achieved. Excellent mineralization is declared for optimized carbon material in several organic pollutants, namely, basic fuchsin, chloramphenicol, phenol and several mixed triphenylmethane-type dyestuffs, with total organic carbon removal of 87.5%, 74.8%, 55.7% and 54.2% within 8 h, respectively. This work offers a valuable insight into facilitating the application of supramolecular-derived carbon materials for extensive EF degradation.

Turning Waste into Treasure: Regulating the Oxygen Corrosion on Fe Foam for Efficient Electrocatalysis.

Iron corrosion causes a great damage to the economy due to the function attenuation of iron-based devices. However, the corrosion products can be used as active materials for some electrocatalytic reactions, such as oxygen evolution reaction (OER). Herein, the oxygen corrosion on Fe foams (FF) to synthesize effective self-supporting electrocatalysts for OER, leading to "turning waste into treasure," is regulated. A dual chloride aqueous system of "NaCl-NiCl2 " is employed to tailor the structures and OER properties of corrosion layers. The corrosion behaviors identify that Cl- anions serve as accelerators for oxygen corrosion, while Ni2+ cations guarantee the uniform growth of corrosion layers owing to the appeared chemical plating. The synergistic effect of "NaCl-NiCl2 " generates one of the highest OER activities that only an overpotential of 212 mV is required to achieve 100 mA cm-2 in 1.0 m KOH solution. The as-prepared catalyst also exhibits excellent durability over 168 h (one week) at 100 mA cm-2 and promising application for overall water splitting. Specially, a large self-supporting electrode (9 × 10 cm2 ) is successfully synthesized via this cost-effective and easily scale-up approach. By combining with corrosion science, this work provides a significant stepping stone in exploring high-performance OER electrocatalysts.

Hierarchical Bimetallic Ni-Co-P Microflowers with Ultrathin Nanosheet Arrays for Efficient Hydrogen Evolution Reaction over All pH Values.

Designing efficient nonprecious catalysts with pH-universal hydrogen evolution reaction (HER) performance is of importance for boosting water splitting. Herein, a self-template strategy based on Ni-Co-glycerates is developed to prepare bimetallic Ni-Co-P microflowers with ultrathin nanosheet arrays. The highly porous core-shell structure gives rise to affluent mass transfer channels and availably prevents the aggregation of nanosheets, while the ultrathin nanosheets are favorable for producing abundant active sites. Besides, the produced CoP/NiCoP heterostructure in the bimetallic Ni-Co-P catalyst has excellent HER performance in a wide pH range. The as-prepared catalyst shows low potentials of 90, 157, and 121 mV to deliver a current density of 10 mA cm-2 in 0.5 M H2SO4, 0.5 M PBS, and 1 M KOH solution, respectively. Meanwhile, negligible overpotential decay is achieved in the polarization curves after a long-term stability determination. This work supplies a promising strategy for developing pH-universal HER electrocatalysts based on solid-state metal alkoxides.

Facile self-template fabrication of hierarchical nickel-cobalt phosphide hollow nanoflowers with enhanced hydrogen generation performance.

Developing facile methods to construct hierarchical-structured transition metal phosphides is beneficial for achieving high-efficiency hydrogen evolution catalysts. Herein, a self-template strategy of hydrothermal treatment of solid Ni-Co glycerate nanospheres followed by phosphorization is delivered to synthesize hierarchical NiCoP hollow nanoflowers with ultrathin nanosheet assembly. The microstructure of NiCoP can be availably tailored by adjusting the hydrothermal treatment temperature through affecting the hydrolysis process of Ni-Co glycerate nanospheres and the occurred Kirkendall effect. Benefitting from the promoted exposure of active sites and affluent mass diffusion routes, the HER performance of the NiCoP hollow nanoflowers has been obviously enhanced in contrast with the solid NiCoP nanospheres. The fabricated NiCoP hollow nanoflowers yield the current density of 10 mA cm-2 at small overpotentials of 95 and 127 mV in 0.5 mol L-1 H2SO4 and 1.0 mol L-1 KOH solution, respectively. Moreover, the two-electrode alkaline cell assembled with the NiCoP and Ir/C catalysts exhibits sustainable stability for overall water splitting. The work provides a simple but efficient method to regulate the microstructure of transition metal phosphides, which is helpful for achieving high-performance hydrogen evolution catalysts based on solid-state metal alkoxides.

A gel single ion conducting polymer electrolyte enables durable and safe lithium ion batteries via graft polymerization.

Concentration polarization issues and lithium dendrite formation, which associate inherently with the commercial dual-ion electrolytes, restrict the performance of lithium ion batteries. Single ion conducting polymer electrolytes (SIPEs) with high lithium ion transference numbers (t + ≈ 1) are being intensively studied to circumvent these issues. Herein, poly(ethylene-co-vinyl alcohol) (EVOH) is chosen as the backbone and then grafted with lithium 3-chloropropanesulfonyl(trifluoromethanesulfonyl)imide (LiCPSI) via Williamson's reaction, resulting in a side-chain-grafted single ion polymer conductor (EVOH-graft-LiCPSI). The ionomer is further blended with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) by solution casting for practical use. The SIPE membrane with ethylene carbonate and dimethyl carbonate (EC/DMC = 1 : 1, v/v) as plasticizer (i.e., gel SIPE) exhibits an ionic conductivity of 5.7 × 10-5 S cm-1, a lithium ion transference number of 0.88, a wide electrochemical window of 4.8 V (vs. Li/Li+) and adequate mechanical strength. Finally, the gel SIPE is applied in a lithium ion battery as the electrolyte as well as the separator, delivering an initial discharge capacity of 100 mA h g-1 at 1C which remains at 95 mA h g-1 after 500 cycles.

Ordered Single-Crystalline Anatase TiO2 Nanorod Clusters Planted on Graphene for Fast Charge Transfer in Photoelectrochemical Solar Cells.

Achieving efficient charge transport is a great challenge in nanostructured TiO2 -electrode-based photoelectrochemical cells. Inspired by excellent directional charge transport and the well-known electroconductibility of 1D anatase TiO2 nanostructured materials and graphene, respectively, planting ordered, single-crystalline anatase TiO2 nanorod clusters on graphene sheets (rGO/ATRCs) via a facial one-pot solvothermal method is reported. The hierarchical rGO/ATRCs nanostructure can serve as an efficient light-harvesting electrode for dye-sensitized solar cells. In addition, the obtained high-crystallinity anatase TiO2 nanorods in rGO/ATRCs possess a lower density of trap states, thus facilitating diffusion-driven charge transport and suppressing electron recombination. Moreover, the novel architecture significantly enhances the trap-free charge diffusion coefficient, which contributes to superior electron mobility properties. By virtue of more efficient charge transport and higher energy conversion efficiency, the rGO/ATRCs developed in this work show significant advantages over conventional rGO-TiO2 nanoparticle counterparts in photoelectrochemical cells.