An efficient nickel hydrogen oxidation catalyst for hydroxide exchange membrane fuel cells.

The hydroxide exchange membrane fuel cell (HEMFC) is a promising energy conversion technology but is limited by the need for platinum group metal (PGM) electrocatalysts, especially for the hydrogen oxidation reaction (HOR). Here we report a Ni-based HOR catalyst that exhibits an electrochemical surface area-normalized exchange current density of 70 µA cm-2, the highest among PGM-free catalysts. The catalyst comprises Ni nanoparticles embedded in a nitrogen-doped carbon support. According to X-ray and ultraviolet photoelectron spectroscopy as well as H2 chemisorption data, the electronic interaction between the Ni nanoparticles and the support leads to balanced hydrogen and hydroxide binding energies, which are the likely origin of the catalyst's high activity. PGM-free HEMFCs employing this Ni-based HOR catalyst give a peak power density of 488 mW cm-2, up to 6.4 times higher than previous best-performing analogous HEMFCs. This work demonstrates the feasibility of efficient PGM-free HEMFCs.

Sustainable Materials: Production Methods and End-of-life Strategies.

All three natural polymers of biomass and the monomer platforms derived from them present multiple avenues to develop products from specialty to bulk markets, which could serve as entry points into the industry for bio based sustainable materials. However, several roadblocks still exist in the pathway of technology development of these materials due to challenges related to cost-competitiveness, scalability, performance and sustainability. This review outlines these major technical challenges as four key checkpoints (cost-competitive, scalability, sustainability, performance) to be addressed for successful market entry of a new sustainable material.

Aldehyde-Assisted Lignocellulose Fractionation Provides Unique Lignin Oligomers for the Design of Tunable Polyurethane Bioresins.

Thanks to chemical stabilization, aldehyde-assisted fractionation (AAF) of lignocellulosic biomass has recently emerged as a powerful tool for the production of largely uncondensed lignin. Depolymerization of AAF lignin via ether cleavage provides aromatic monomers at near theoretical yields based on ether cleavage and an oligomeric fraction that remains largely unexploited despite its unique material properties. Here, we present an in-depth analytical characterization of AAF oligomers derived from hardwood and softwood in order to elucidate their molecular structures. These bioaromatic oligomers surpass technical Kraft lignin in terms of purity, solubility, and functionality and thus cannot even be compared to this common feedstock directly for material production. Instead, we performed comparative experiments with Kraft oligomers of similar molecular weight (Mn ∼ 1000) obtained through solvent extraction. These oligomers were then formulated into polyurethane materials. Substantial differences in material properties were observed depending on the amount of lignin, the botanical origin, and the biorefining process (AAF vs Kraft), suggesting new design principles for lignin-derived biopolymers with tailored properties. These results highlight the surprising versatility of AAF oligomers towards the design of new biomaterials and further demonstrate that AAF can enable the conversion of all biomass fractions into value-added products.

Slowing the Kinetics of Alumina Sol-Gel Chemistry for Controlled Catalyst Overcoating and Improved Catalyst Stability and Selectivity.

Catalyst overcoating is an emerging approach to engineer surface functionalities on supported metal catalyst and improve catalyst selectivity and durability. Alumina deposition on high surface area material by sol-gel chemistry is traditionally difficult to control due to the fast hydrolysis kinetics of aluminum-alkoxide precursors. Here, sol-gel chemistry methods are adapted to slow down these kinetics and deposit nanometer-scale alumina overcoats. The alumina overcoats are comparable in conformality and thickness control to overcoats prepared by atomic layer deposition even on high surface area substrates. The strategy relies on regulating the hydrolysis/condensation kinetics of Al(s BuO)3 by either adding a chelating agent or using nonhydrolytic sol-gel chemistry. These two approaches produce overcoats with similar chemical properties but distinct physical textures. With chelation chemistry, a mild method compatible with supported base metal catalysts, a conformal yet porous overcoat leads to a highly sintering-resistant Cu catalyst for liquid-phase furfural hydrogenation. With the nonhydrolytic sol-gel route, a denser Al2 O3 overcoat can be deposited to create a high density of Lewis acid-metal interface sites over Pt on mesoporous silica. The resulting material has a substantially increased hydrodeoxygenation activity for the conversion of lignin-derived 4-propylguaiacol into propylcyclohexane with up to 87% selectivity.

Densely Packed, Ultra Small SnO Nanoparticles for Enhanced Activity and Selectivity in Electrochemical CO2 Reduction.

Controlling the selectivity in electrochemical CO2 reduction is an unsolved challenge. While tin (Sn) has emerged as a promising non-precious catalyst for CO2 electroreduction, most Sn-based catalysts produce formate as the major product, which is less desirable than CO in terms of separation and further use. Tin monoxide (SnO) nanoparticles supported on carbon black were synthesized and assembled and their application in CO2 reduction was studied. Remarkably high selectivity and partial current densities for CO formation were obtained using these SnO nanoparticles compared to other Sn catalysts. The high activity is attributed to the ultra-small size of the nanoparticles (2.6 nm), while the high selectivity is attributed to a local pH effect arising from the dense packing of nanoparticles in the conductive carbon black matrix.

Improving Heterogeneous Catalyst Stability for Liquid-phase Biomass Conversion and Reforming.

Biomass is a possible renewable alternative to fossil carbon sources. Today, many bio-resources can be converted to direct substitutes or suitable alternatives to fossil-based fuels and chemicals. However, catalyst deactivation under the harsh, often liquid-phase reaction conditions required for biomass treatment is a major obstacle to developing processes that can compete with the petrochemical industry. This review presents recently developed strategies to limit reversible and irreversible catalyst deactivation such as metal sintering and leaching, metal poisoning and support collapse. Methods aiming to increase catalyst lifetime include passivation of low-stability atoms by overcoating, creation of microenvironments hostile to poisons, improvement of metal stability, or reduction of deactivation by process engineering.

Fast characterization of functionalized silica materials by silicon-29 surface-enhanced NMR spectroscopy using dynamic nuclear polarization.

We demonstrate fast characterization of the distribution of surface bonding modes and interactions in a series of functionalized materials via surface-enhanced nuclear magnetic resonance spectroscopy using dynamic nuclear polarization (DNP). Surface-enhanced silicon-29 DNP NMR spectra were obtained by using incipient wetness impregnation of the sample with a solution containing a polarizing radical (TOTAPOL). We identify and compare the bonding topology of functional groups in materials obtained via a sol-gel process and in materials prepared by post-grafting reactions. Furthermore, the remarkable gain in time provided by surface-enhanced silicon-29 DNP NMR spectroscopy (typically on the order of a factor 400) allows the facile acquisition of two-dimensional correlation spectra.

Chemistry of nitrosyliron complexes supported by a ß-diketiminate ligand.

Several nitrosyl complexes of Fe and Co have been prepared using the sterically hindered Ar-nacnac ligand (Ar-nacnac = anion of [(2,6-diisopropylphenyl)NC(Me)](2)CH). The dinitrosyliron complexes [Fe(NO)(2)(Ar-nacnac)] (1) and (Bu(4)N)[Fe(NO)(2)(Ar-nacnac)] (2) react with [Fe(III)(TPP)Cl] (TPP = tetraphenylporphine dianion) to generate [Fe(II)(NO)(TPP)] and the corresponding mononitrosyliron complexes. The factors governing NO transfer with dinitrosyliron complexes (DNICs) 1 and 2 are evaluated, together with the chemistry of the related mononitrosyliron complex, [Fe(NO)Br(Ar-nacnac)] (4). The synthesis and properties of the related cobalt dinitrosyl [Co(NO)(2)(Ar-nacnac)] (3) is also discussed for comparison to DNICs 1 and 2. The solid-state structures of several of these compounds as determined by X-ray crystallography are reported.

Increasing the activity of the Cu/CuAl2O4/Al2O3 catalyst for the RWGS through preserving the Cu2+ ions.

Cu-Al spinel oxide is a highly active catalyst for CO2 conversion to CO. However, it suffers from low surface area. By depositing a silica layer, we protected the catalyst surface and preserved the Cu2+ ions during the calcination process. These ions form well-dispersed Cu sites which participate in the reaction.

Formaldehyde stabilization facilitates lignin monomer production during biomass depolymerization.

Practical, high-yield lignin depolymerization methods could greatly increase biorefinery productivity and profitability. However, development of these methods is limited by the presence of interunit carbon-carbon bonds within native lignin, and further by formation of such linkages during lignin extraction. We report that adding formaldehyde during biomass pretreatment produces a soluble lignin fraction that can be converted to guaiacyl and syringyl monomers at near theoretical yields during subsequent hydrogenolysis (47 mole % of Klason lignin for beech and 78 mole % for a high-syringyl transgenic poplar). These yields were three to seven times those obtained without formaldehyde, which prevented lignin condensation by forming 1,3-dioxane structures with lignin side-chain hydroxyl groups. By depolymerizing cellulose, hemicelluloses, and lignin separately, monomer yields were between 76 and 90 mole % for these three major biomass fractions.