Despite over a century of study and decades of intensive research, few fuel cell products have appeared on the market. [1] The major inhibitor to mass commercialisation is cost. [2] H 2 /air alkaline fuel cells (AFCs) containing KOH(aq) electrolyte promise the lowest cost devices, [3,4] with the ability to use non-Pt catalysts. The fundamental problem with AFCs is that the KOH(aq) electrolyte reacts with CO 2 (cathode air supply) to form carbonate species, which lowers cell performance and lifetime (formation of carbonate precipitates in electrodes and reduction of OH -concentration in electrolyte). [4,5] However, the carbonate content of a aqueous-electrolyte-free (metal-cation-free) alkaline anion-exchange membrane (AAEM), that was pre-exchanged to the CO 3 2-form, decreased when operated in H 2 /air and methanol/air fuel cells. This remarkable result is contrary to prior wisdom; AAEMs inherently prevent carbonate performance losses when incorporated into AFCs. This experiment was made possible only by the recent breakthrough development of an alkaline interface ionomer, [6] which allows fabrication of membrane electrode assemblies that do not require incorporation of metal hydroxides species to perform well. [7] The widely perceived advantages of alkaline membrane direct alcohol fuel cells (AMDAFC) are the potential use of relatively inexpensive and abundant non-Pt electrocatalysts (as with the H 2 /air AFCs), [8][9][10] reduced alcohol crossover, [11,12] and enhanced electro-oxidation of high energy density alcoholic fuels. [13] However, metal hydroxides have traditionally been used as an additive, either in the electrode architectures [7] or in the aqueous alcohol supplies [11] due to the previous lack of an alkaline analogue to the perfluorosulfonic acid dispersions, [14] required for high-performance membrane electrode assemblies (MEAs) for proton-exchange membrane fuel cells (PEMFCs). Concerns persist about the effect of carbonate formation with such AMDAFCs. [15] The hypothesis that was tested in this study is that the tendency to form CO 3 2-can be reduced on the elimination of M n+ from AAEM-based solid alkaline fuel cells (SAFCs); precipitates of metal carbonates [4] cannot then form (the counter -N + R 3 cations are covalently bound to the polymer electrolyte analogous to the -SO 3 -counter anions in PEMs). The data presented in Table 1 compare the ex situ properties of the AAEM in CO 3 2-and OH -forms; the properties do not vary substantially. Importantly, the through-membrane conductivities at 30°C in a static relative humidity (RH) = 100% atmosphere were similar. The ionic performance of AAEMs would not be seriously compromised even on substantial formation of carbonate.Peak power densities of 37.9 ± 1.4 mW cm -2 were obtained in H 2 /air fuel cell tests with the AAEM MEAs in CO 3 2-form ( Figure 1); this was higher than the 32.9 ± 1.6 mW cm -2 obtained with the OH -benchmarks. The respective in situ cell resistances of 1.5 ± 0.2 Ω cm 2 and 1.7 ± 0.2 Ω cm 2 showed that there was only a small in...

Three tetravalent actinide (An ) hexanuclear clusters with the octahedral core [An (OH) O ] (An =U , Np , Pu ) were structurally characterized in the solid state and in aqueous solution by using single-crystal X-ray diffraction, X-ray absorption, IR, Raman, and UV/Vis spectroscopy. The observed structure, [An (OH) O (H O) (HDOTA) ]⋅HCl/HNO ⋅n H O (An=U(I), Np(II), Pu(III)), consists of a An hexanuclear pseudo-octahedral cluster stabilized by DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) ligands. The six actinide atoms are connected through alternate μ -O and μ -OH groups. Extended X-ray absorption fine structure (EXAFS) investigations combined with UV/Vis spectroscopy provide evidence for the same local structure in moderate acidic and neutral aqueous solutions. The synthesis mechanism was partially elucidated and the main physicochemical properties (pH range stability, solubility, and protonation constant) of the cluster were determined. The results underline the importance of: 1) considering such polynuclear species in thermodynamic models, and 2) competing reactions between hydrolysis and complexation. It is interesting to note that the same synthesis route with thorium(IV) led to the formation of a dimer, Th (H O) (H DOTA) ⋅4 NO ⋅x H O (IV), which contrasts to the structure of the other An hexamers.

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The singular Pu IV hexanuclear cluster [Pu 6 (OH) 4 O 4 ] 12+ stabilized by 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) ligands was structurally characterized for the first time both in the solid state and in water solution by using X-ray diffraction and X-ray absorption and UV/Vis spectroscopy.

Aqueous-electrolyte-free (metal-cation-free) alkaline membrane fuel cells represent a promising new class of low-temperature Pt-free fuel cell. A current hypothesis is that mass transport of (stoichiometric) reactant water to the cathode catalyst reaction sites is the principal origin of the limited power output (water is not a direct reactant in proton-exchange membrane fuel cells (PEMFCs) and only required to keep the protonexchange membrane hydrated for sufficient conductivity); electrode architectures specifically optimized for use in H 2 /O 2 solid polymer electrolyte alkaline fuel cells (SPE-AFC) were previously identified as a research priority. This study directly addresses this challenge and shows that with the correct choice of cathode components significant improvements in power performance can be obtained; 125 mW cm -2 was obtained in a H 2 /O 2 SPE-AFC when a cathode fabricated from Toray carbon paper and Pt/C catalyst (20% mass Pt on Vulcan XC-72R carbon support) was used with a 79 µm thick anion-exchange membrane in hydroxide anion form (cf. 94 mW cm -2 when the same membrane was used with prefabricated Pt-based commercial carbon cloth electrodes that contained 4 mg cm -2 metal loadings and poly(tetrafluoroethylene), PTFE, binder). Importantly, the cathode fabrication methodology reported will allow the easy comparison of the performance of different cathode catalysts, including Pt/C and cheaper carbon-supported non-noble-metal-containing catalysts of different formulations (e.g., different carbon supports and metal particle sizes). A final significant finding was that Pt-free Vulcan XC-72R-only cathodes can produce between 25% and 36% of the power obtained when Pt/C catalysts were used in SPE-AFCs (this is not the case with PEMFCs where carbon is electrokinetically inactive for the oxygen reduction reaction at the cathode); this insight highlights the necessity of recording the background currents, arising from the carbon supports, when testing different catalyst formulations in alkaline media. A recommendation is presented for a standardized test protocol for evaluating these inherently CO 2 -tolerant fuel cells.

The structures of plutonium(IV) and uranium(VI) ions with a series of N,N-dialkyl amides ligands with linear and branched alkyl chains were elucidated from single-crystal X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS), and theoretical calculations. In the field of nuclear fuel reprocessing, N,N-dialkyl amides are alternative organic ligands to achieve the separation of uranium(VI) and plutonium(IV) from highly concentrated nitric acid solution. EXAFS analysis combined with XRD shows that the coordination structure of U(VI) is identical in the solution and in the solid state and is independent of the alkyl chain: two amide ligands and four bidentate nitrate ions coordinate the uranyl ion. With linear alkyl chain amides, Pu(IV) also adopt identical structures in the solid state and in solution with two amides and four bidentate nitrate ions. With branched alkyl chain amides, the coordination structure of Pu(IV) was more difficult to establish unambiguously from EXAFS. Density functional theory (DFT) calculations were consequently performed on a series of structures with different coordination modes. Structural parameters and Debye-Waller factors derived from the DFT calculations were used to compute EXAFS spectra without using fitting parameters. By using this methodology, it was possible to show that the branched alkyl chain amides form partly outer-sphere complexes with protonated ligands hydrogen bonded to nitrate ions.

The mixed-actinide uranium(IV)-plutonium(III) oxalate single crystals (NH4)0.5[Pu(III)0.5U(IV)0.5(C2O4)2·H2O]·nH2O (1) and (NH4)2.7Pu(III)0.7U(IV)1.3(C2O4)5·nH2O (2) have been prepared by the diffusion of different ions through membranes separating compartments of a triple cell. UV-vis, Raman, and thermal ionization mass spectrometry analyses demonstrate the presence of both uranium and plutonium metal cations with conservation of the initial oxidation state, U(IV) and Pu(III), and the formation of mixed-valence, mixed-actinide oxalate compounds. The structure of 1 and an average structure of 2 were determined by single-crystal X-ray diffraction and were solved by direct methods and Fourier difference techniques. Compounds 1 and 2 are the first mixed uranium(IV)-plutonium(III) compounds to be structurally characterized by single-crystal X-ray diffraction. The structure of 1, space group P4/n, a = 8.8558(3) Å, b = 7.8963(2) Å, Z = 2, consists of layers formed by four-membered rings of the two actinide metals occupying the same crystallographic site connected through oxalate ions. The actinide atoms are nine-coordinated by oxygen atoms from four bidentate oxalate ligands and one water molecule, which alternates up and down the layer. The single-charged cations and nonbonded water molecules are disordered in the same crystallographic site. For compound 2, an average structure has been determined in space group P6/mmm with a = 11.158(2) Å and c = 6.400(1) Å. The honeycomb-like framework [Pu(III)0.7U(IV)1.3(C2O4)5](2.7-) results from a three-dimensional arrangement of mixed (U0.65Pu0.35)O10 polyhedra connected by five bis-bidentate μ(2)-oxalate ions in a trigonal-bipyramidal configuration.

In industrial nuclear fuel reprocessing, small amounts of ruthenium are extracted by tri-n-butyl-phosphate (TBP) at the same time as uranium and plutonium. This behavior increases solvent radiolysis and requires secondary extraction cycles to minimize the residual ruthenium content in uranium and plutonium products. However, the solvent ruthenium extraction mechanism remains largely unexplored. This study addresses the speciation of ruthenium in solvent extraction conditions by complementary infrared and X-ray absorption spectroscopy. First, spectroscopic result interpretation is supported by a single crystal X-ray diffraction study on reference compounds to unambiguously demonstrate that the ruthenium extraction mechanism is driven by a weak outer-sphere Ru–TBP interaction. Second, the ruthenium coordination sphere is quantitatively characterized. Ruthenium speciation in the organic phase depends on the initial aqueous phase, and both monomeric ruthenium nitrosyl trinitrate complexes and a hydrolyzed dimeric ruthenium nitrosyl complex are shown. Average coordination numbers for nitrate, hydroxide, and aquo ligands are accurately determined in both phases, by applying a constrained EXAFS fit approach.