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Iron and nitrogen doping of carbon materials is one of the promising pathways towards replacing Pt/C in polymer electrolyte fuel cell cathodes. Here, we show a synthesis method to produce highly active non-precious metal catalysts and study the effect of synthesis parameters on the oxygen reduction reaction (ORR) activity in high-pH conditions. The electrocatalysts are prepared by functionalizing silicon carbide-derived carbon (SiCDC) with 1,10-phenanthroline, iron(II)acetate and, optionally polyvinylpyrrolidone, by ball-milling with ZrO 2 in dry or wet conditions, followed by pyrolysis at 800 °C. The catalysts are characterized by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, N 2 physisorption and inductively coupled plasma mass spectrometry. By optimizing the ball-milling conditions, we achieved a reduction in the size of SiCDC grains from >1 μm to 200 nm without negatively affecting the high BET area of catalysts derived from SiCDC. This resulted in increased ORR activity in both rotating disk electrode and anion exchange membrane fuel cell (AEMFC) environments, and improved mass-transport properties of the cathode layer in fuel cell. The ORR activity at 0.9 V in AEMFC of the optimized iron and nitrogen-doped SiCDC reaches 52 mA cm−2, exceeding that of a Pt/C cathode at 36.5 mA cm−2. Image 1 • Fe, N co-doped silicon carbide-derived carbon catalysts were used for ORR studies. • The effect of ball size on the ORR activity of milled carbon catalysts was studied. • 0.5 mm balls decrease the size of final catalyst particles to under 1 μm. • Addition of PVP further decreased the catalyst particle size and increased ORR activity. • P max of 356 mW cm−2 and 52 mA cm−2 at 0.9 V reached in AEMFC by best catalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] • Green recycling process of cathode materials from LIBs using supercritical CO 2. • scCO 2 as a green solvent for critical metal extraction at 60 °C and 250 bar. • Poly(VBPDA- co -FDA) copolymer as leaching agent, macro-ligand, and extracting agent. • H 2 O 2 and ethanol as reducing agent for Co2+ complexation in scCO 2 from LiCo(III)O 2. • Recovery yield up to 75 % of Co and Li from LiCoO 2. Supercritical CO 2 (scCO 2) extraction assisted by complexing copolymers is a promising process to recover valuable metals from lithium-ion batteries (LIBs). CO 2 , in addition to being non-toxic, abundant and non-flammable, allows an easy separation of metal-complexes from the extraction medium by depressurization, limiting the wastewater production. In this study, CO 2 -philic gradient copolymers bearing phosphonic diacid complexing groups (poly(vinylbenzylphosphonic diacid- co -1,1,2,2-tetrahydroperfluorodecylacrylate), p(VBPDA- co -FDA)) were synthesized for the extraction of lithium and cobalt from LiCoO 2 cathode material. Notably, the copolymer was able to play the triple role of leaching agent, complexing agent and surfactant. The proof of concept for leaching, complexation and extraction was achieved, using two different extraction systems. A first extraction system used aqueous hydrogen peroxide as reducing agent while it was replaced by ethanol in the second extraction system. The scCO 2 extraction conditions such as extraction time, temperature, functional copolymer concentration, and the presence of additives were optimized to improve the metals extraction from LiCoO 2 cathode material, leading to an extraction efficiency of Li and Co up to ca. 75 % at 60 °C and 250 bar. [ABSTRACT FROM AUTHOR]

We designed stable and highly reproducible hydrogels by external unidirectional diffusion of Fe 2+ ions into aqueous solutions of polygalacturonate (polyGal) chains. The Fe 2+ ions act as cross-linkers between the Gal units in such a way that both the molar ratio R ([Fe 2+ ]/[Gal units] = 0.25) and the mesh size of the polyGal network at the local scale (ξ = 75 ± 5 Å) have constant values within the whole gel, as respectively determined by titration and Small Angle Neutron Scattering. From macroscopic point of view, there is a progressive decrease of polyGal concentration from the part of the gel formed in the early stages of the gelation process, which is homogeneous, transparent and whose Young modulus has a high value of ∼10 5  Pa, up to the part of the gel formed in the late stages, which is heterogeneous, highly turbid and has a much lower Young modulus of ∼10 3  Pa. Since the local organization of the polyGal chains remains identical all along the hydrogels, this macroscopic concentration gradient originates from the formation of heterogeneities at a mesoscopic length scale during the gelation process. In addition, X-ray Absorption Spectroscopy measurements remarkably reveal that Fe 2+ ions keep their +II oxidation state in the whole gels once they have cross-linked the Gal units. These polyGal hydrogels thus protect iron against oxidation and could be used for iron fortification. [ABSTRACT FROM AUTHOR]

The electrocatalytic behaviour of single-phase Ru 1-x Ti x O 2 materials was studied to outline general trends controlling the selectivity of oxide-based anodes in parallel oxygen evolution and chlorine evolution reactions. Materials with x ranging between 0 and 0.2 were prepared by spray freeze freeze drying approach. Prepared materials show a non-homogeneous distribution of Ti in the structure with dominant clustering of the Ti along the (001) direction. For materials with x higher than 0.1 the dominant linear clustering of Ti along the z-axis changes, including Ti clustering also along (111) direction. Prepared materials are active in both oxygen evolution and chlorine evolution reactions. The Ti has a pronounced effect on the selectivity of the prepared materials. Ti presence affects the selectivity of the prepared materials in a complex manner. Materials featuring a low Ti content (x∼0.05) retain a preference for oxygen evolution reaction even in presence of chlorides and are more selective for oxygen evolution than pure RuO 2. The selectivity towards chlorine evolution increases with increasing Ti content and, apparently, also with clustering of Ti along the (111) direction. The selectivity towards chlorine evolution may be related to the tendency of the prepared catalysts to evolve the oxygen via lattice oxygen evolution reaction (LOER) reflecting the ability of the catalyst surface to form active sites under operando conditions. [ABSTRACT FROM AUTHOR]

We have examined the electrocatalytic activity of iron phthalocyanine (FePc) and perchlorinated iron phthalocyanine 16(Cl)FePc for the oxygen reduction reaction (ORR) in alkaline medium with the two molecules either adsorbed on the external surface of single-wall carbon nanotubes (SWCNT) or covalently anchored via an axial pyridine ligand on pyridine-functionalized single-wall carbon nanotubes (py-SWCNT). Regardless of the particular phthalocyanine type, the ORR activity is higher when the substrate is py-SWCNT rather than SWCNT. The Tafel slopes for ORR are very similar for the two Fe macrocyclic complexes attached to SWCNTs in the two different configurations, suggesting a common rate-determining step for the ORR for all four catalysts. It is also observed that, for both the SWCNT and py-SWCNT supports, the ORR activity is higher for 16(Cl)FePc than for FePc. This is attributed to the electron-withdrawing effect of the peripheral and non-peripheral chlorine atoms in the macrocyclic ligand. While FeN4 macrocycles are known to be located on the strong binding side of a volcano correlation including several MN4 species, the chlorine substituents decrease the binding energy of O 2 on the central Fe cation, thereby moving up the macrocycle catalyst towards the apex of the volcano correlation. Both the carbon surface and macrocyclic ligand effects were optimized with 16(Cl)FePc attached to py-SWCNT, which is more active than both FePc on SWCNT and FePc on py-SWCNT. Here we show that both the axial ligand and the electron withdrawing groups (-Cl) have a combined collaborative effect in increasing the catalytic activity for ORR of Fe-phthalocyanines confined on the external walls of single-wall carbon nanotubes. [Display omitted] [ABSTRACT FROM AUTHOR]