An approach to the industrial-scale conversion of CO2 through electrolysis is realized in this work. Such a device is fully based on alkaline polymer electrolytes, both as the membrane and the ionomer inside electrodes, and works only with pure water. Typical current density is 500 mA cm−2 @ 3V 60 °C, with the faradaic efficiency of CO production over 90%.

Anion-exchange membranes (AEM) containing saturated-heterocyclic benzyl-quaternary ammonium (QA) groups synthesised by radiation-grafting onto poly(ethylene-co-tetrafluoroethylene) (ETFE) films are reported. The relative properties of these AEMs are compared with the benchmark radiation-grafted ETFE-g-poly(vinylbenzyltrimethylammonium) AEM. Two AEMs containing heterocyclic-QA head groups were down-selected with higher relative stabilities in aqueous KOH (1 mol dm-3) at 80°C (compared to the benchmark): these 100 μm thick (fully hydrated) ETFE-g-poly(vinylbenzyl-Nmethylpiperidinium)- and ETFE-g-poly(vinylbenzyl-N-methylpyrrolidinium)-based AEMs had as-synthesised ion-exchange capacities (IEC) of 1.64 and 1.66 mmol g-1, respectively, which reduced to 1.36 mmol dm-3 (ca. 17 – 18% loss of IEC) after alkali ageing (the benchmark AEM showed 30% loss of IEC under the same conditions). These down-selected AEMs exhibited as-synthesised Cl- ion conductivities of 49 and 52 mS cm-1, respectively, at 90°C in a 95% relative humidity atmosphere, while the OH- forms exhibited conductivities of 138 and 159 mS cm-1, respectively, at 80°C in a 95% relative humidity atmosphere. The ETFE-g-poly(vinylbenzyl-N-methylpyrrolidinium)-based AEM produced the highest performances when tested as catalyst coated membranes in H2/O2 alkaline polymer electrolyte fuel cells at 60°C with PtRu/C anodes, Pt/C cathodes, and a polysulfone ionomer: the 100 μm thick variant (synthesised from 50 μm thick ETFE) yielded peak power densities of 800 and 630 mW cm-2 (with and without 0.1 MPa back pressurisation, respectively), while a 52 μm thick variant (synthesised from 25 μm thick ETFE) yielded 980 and 800 mW cm-2 under the same conditions. From these results, we make the recommendation that developers of AEMs, especially pendent benzyl-QA types, should consider the benzyl-Nmethylpyrrolidinium head-group as an improvement to the current de facto benchmark benzyltrimethylammonium headgroup

No abstract

Powered by renewable electricity, the electrochemical conversion of CO2 to liquid fuels and valuable chemicals is a meaningful approach to enable carbon cycling and tackle environmental issues. An intrinsic challenge has been the low efficiency and selectivity, in particular for deep reduction products. Here, we report on an interface-enhanced strategy for transforming the catalytic selectivity toward the CO2 reduction reaction (CO2RR). Inspired by the enzyme catalysis in nature, where the catalytic center is surrounded by a chemically selective environment, we create a thin layer of nitrogen-doped carbon (N x C) over the Cu surface. The N x C environment does not modify the electronic property of Cu but selectively enriches and activates CO2 molecules through the specific N–CO2 interaction, as experimentally identified. Such a Cu/N x C interface has boosted the faradic efficiency (FE) of the CO2RR to be above 90%, with the C2 products (ethylene and ethanol) being the majority (80% in total FE). The N x C overlayer also protects well the Cu substrate from the morphological change, thus increasing the catalytic stability. Our findings manifest that the chemical environment over the metal surface indeed plays a crucial, but not well recognized, role in selectivity control, which can hardly be achieved by solely tuning the electronic structure of metal catalysts.

Fe-containing N-doped carbons (Fe/N/C) are a promising Pt-alternative catalyst for the oxygen reduction reaction (ORR) and are believed to be more stable in alkaline media than in acids and thus particularly suitable to be applied as the cathode catalyst for alkaline polymer electrolyte fuel cells (APEFCs). However, there has hitherto been no successful report on high-performance APEFC based on the Fe/N/C cathode, the reason for which is still not quite clear. Here we report a highperformance Fe/N/C catalyst and its application in APEFC. The catalyst precursor is adenosine, an environmentally benign Nrich biomolecule, which is polymerized via a solvothermal process and then carbonized through pyrolysis. The resulting Fe/N/C nanotubes are thoroughly characterized by a variety of microscopy and spectroscopy (SEM, TEM, XRD, XPS, Raman, Mossbauer, and STEM-EELS), which reveal a high surface N/C ratio (8 at%) and atomic Fe sites well dispersed at the wall of the nanotubes. The catalytic sites are identified to be Fe−N 4 . The volume-specific catalytic activity of the Fe/N/C catalyst toward the ORR is as good as that of the commercial 20 wt % Pt/C catalyst in alkaline solutions, and better in durability. The electronic conductivity of Fe/N/C turns out to be trivial in rotating-disk electrode experiments but key for fuel cell tests. The APEFC with Fe/N/C cathode (2 mg/cm 2 in catalyst loading) exhibits a peak power density greater than 450 mW/cm 2 , the thus-far highest record in the literature for APEFC using a nonprecious metal cathode. Our findings not only deepen the understanding of the structure−activity relationship of the Fe/N/C catalyst but also mark a step toward its real application in APEFC.