Ionic Liquid-Derived Carbon-Supported Metal Electrocatalysts as Anodes in Direct Borohydride-Peroxide Fuel Cells

Three different carbon-supported metal (gold, platinum, nickel) nanoparticle (M/c-IL) electrocatalysts are prepared by template-free carbonization of the corresponding ionic liquids, namely [Hmim][AuCl4], [Hmim]2[PtCl4], and [C16mim]2[NiCl4], as confirmed by X-ray diffraction analysis, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and Raman spectroscopy. The electrochemical investigation of borohydride oxidation reaction (BOR) at the three electrocatalysts by cyclic voltammetry reveals different behavior for each material. BOR is found to be a first-order reaction at the three electrocatalysts, with an apparent activation energy of 10.6 and 13.8 kJ mol−1 for Pt/c-IL and Au/c-IL electrocatalysts, respectively. A number of exchanged electrons of 5.0, 2.4, and 2.0 is obtained for BOR at Pt/c-IL, Au/c-IL, and Ni/c-IL electrodes, respectively. Direct borohydride-peroxide fuel cell (DBPFC) tests done at temperatures in the 25–65 °C range show ca. four times higher power density when using a Pt/c-IL anode than with an Au/c-IL anode. Peak power densities of 40.6 and 120.5 mW cm−2 are achieved at 25 and 65 °C, respectively, for DBPFC with a Pt/c-IL anode electrocatalyst.

Ultrasound-assisted transformation from waste biomass to efficient carbon-based metal-free pH-universal oxygen reduction reaction electrocatalysts

Efficient carbon-based nitrogen-doped electrocatalysts derived from waste biomass are regarded as a promising alternative to noble metal catalysts for oxygen reduction reaction (ORR), which is crucial to fuel cell performance. Here, coconut palm leaves are employed as the carbon source and a series of nitrogen-doped porous carbons were prepared by virtue of a facile and mild ultrasound-assisted method. The obtained carbon material (ANDC-900-10) conveys excellent pH-universal catalytic activity with onset potentials (E_onset) of 1.01, 0.91 and 0.84 V vs. RHE, half-wave potentials (E_1/2) of 0.87, 0.74 and 0.66 V vs. RHE and limiting current densities (J_L) of 5.50, 5.45 and 4.97 mA cm^-2 in alkaline, neutral and acidic electrolytes, respectively, prevailing over the commercial Pt/C catalyst and, what's more, ANDC-900-10 displays preeminent methanol crossover resistance and long-term stability in the broad pH range (0-13), thanks to its abundant hierarchical nanopores as well as effective nitrogen doping with high-density pyridinic-N and graphitic-N. This work provides sonochemical insight for underpinning the eco-friendly approach to rationally designing versatile metal-free carbon-based catalysts toward the ORR at various pH levels.

Cross-linked poly(ionic liquid) as precursors for nitrogen-doped porous carbons

A soluble and easily dispersive cross-linked poly(ionic liquid), copolymer of 1-vinyl-3-butylimidazolium bromide ([VBIM][Br]) and divinylbenzene (DVB), was used as a precursor for nitrogen doped porous carbons (NPCs) with SiO₂ (from tetraethyl orthosilicate) as a template. The NPCs were characterized by infrared (IR) spectroscopy, nitrogen adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, thermo gravimetric analysis (TGA), elemental analysis and X-ray photoelectron spectroscopy (XPS). The specific surface area and porosity of NPCs depended on the carbonization temperature, the SiO₂/[VBIM][Br] ratio and the precursors. Under the optimized conditions, the NPC prepared from cross-linked poly(ionic liquid), P([VBIM][Br]–0.1DVB), gave a high specific surface area up to 1324 m² g⁻¹. XRD indicated that amorphous and disordered graphitic layers were dominant in NPCs. The nitrogen content was about 4–5 wt% in NPCs, and the nitrogen bonding state observed using XPS analysis was mainly pyridinic- and pyrrolic-N. Meanwhile, the cyclic voltammetry, gravimetric charge–discharge curves and electrochemical impedance spectroscopy of the NPCs were also investigated, the specific capacitance was up to 243 F g⁻¹ at 0.1 A g⁻¹, and the retention ratio was nearly 100% after charge–discharge cycling 2400 times at 2 A g⁻¹ in 6 M KOH electrolyte.

The cross-linked PIL with “network structure” can fabricate nitrogen-doped porous carbons with higher specific surface area.

Achieving high-performance nitrate electrocatalysis with PdCu nanoparticles confined in nitrogen-doped carbon coralline

Complex porous carbon nanostructures with homogeneously embedded nanoparticles and intricate architectures show promise as high-performance catalysts. Herein, we demonstrate a direct surfactant co-assembly approach for the fabrication of well-dispersed PdCu nanoparticles encapsulated in N-doped porous carbon with three-dimensional coralline structures. Owing to their porous features and unique frameworks, the PdxCuy@N-pC coralline-like nanostructures offer large surface areas, accessible active sites, and excellent nitrate electrocatalytic ability. The composite catalyst Pd4Cu4@N-pC exhibits outstanding catalytic performance with a high nitrate removal rate of ∼95%, nitrogen selectivity of ∼80%, and removal capacity of 22 000 mg N per g PdCu. More importantly, the present work opens up a broad horizon for architectures of nanoparticles confined in coralline-like 3D porous carbon structures with superior performance and promising large-scale applications.