Lauren R. Grabstanowicz

Highly Efficient Non-Precious Metal Electrocatalysts Prepared from One-Pot Synthesized Zeolitic Imidazolate Frameworks

A facile synthesis of non-PGM ORR electrocatalysts through thermolysis of one-pot synthesized ZIF is demonstrated. The electrocatalysts exhibit excellent activity, with a maximum volumetric current density of 88.1 A cm(-3) measured at 0.8 V in PEFC tests. This approach not only makes ZIFs-based electrocatalysts easy to scale up, but also paves the way for the tailored synthesis of electrocatalysts.

Highly efficient nonprecious metal catalyst prepared with metal–organic framework in a continuous carbon nanofibrous network

Significance The performance of conventional carbon-supported catalysts is strongly influenced by the support morphology, which contains micropores, mesopores, and macropores. Whereas micropores host the majority of the active sites and macropores promote effective reagent/product mass transfer, mesopores contribute a limited role in both but occupy a significant fraction of the total pore volume. For catalytic applications where maximizing active site number and mass/charge transports with the highest possible catalyst density is essential, conventional carbon supports are no longer suitable. In this paper, we introduce a previously unidentified catalyst’s morphology with a high catalytic active surface concentrated nearly exclusively in micropores while transferring reactant/product via a macroporous nanofiber framework. The nonprecious metal catalyst with such architecture demonstrated unprecedented activity in fuel cell tests. Fuel cell vehicles, the only all-electric technology with a demonstrated >300 miles per fill travel range, use Pt as the electrode catalyst. The high price of Pt creates a major cost barrier for large-scale implementation of polymer electrolyte membrane fuel cells. Nonprecious metal catalysts (NPMCs) represent attractive low-cost alternatives. However, a significantly lower turnover frequency at the individual catalytic site renders the traditional carbon-supported NPMCs inadequate in reaching the desired performance afforded by Pt. Unconventional catalyst design aiming at maximizing the active site density at much improved mass and charge transports is essential for the next-generation NPMC. We report here a method of preparing highly efficient, nanofibrous NPMC for cathodic oxygen reduction reaction by electrospinning a polymer solution containing ferrous organometallics and zeolitic imidazolate framework followed by thermal activation. The catalyst offers a carbon nanonetwork architecture made of microporous nanofibers decorated by uniformly distributed high-density active sites. In a single-cell test, the membrane electrode containing such a catalyst delivered unprecedented volumetric activities of 3.3 A⋅cm−3 at 0.9 V or 450 A⋅cm−3 extrapolated at 0.8 V, representing the highest reported value in the literature. Improved fuel cell durability was also observed.

A Highly Active and Support‐Free Oxygen Reduction Catalyst Prepared from Ultrahigh‐Surface‐Area Porous Polyporphyrin

A new approach for preparing non-precious-metal electrocatalysts using a porous organic polymer (POP) as precursor is presented. Polyporphyrin, containing a high density of nitrogen-coordinated iron macrocyclic centers, was prepared by oxidative coupling to form a porous network with a very high specific surface area and narrow pore-size distribution. Upon pyrolysis, the POP was converted into a highly active electrocatalysts for the oxygen reduction reaction in an acidic electrolyte. Proton-exchange membrane fuel cells, prepared with such catalyst at the cathode, achieved very high measured volumetric and gravimetric current densities of 20.2 Acm 3 and 39.4 Ag 1 at 0.8 V, respectively, and a peak power density of 730 mWcm 2 at 0.4 V. The proton-exchange membrane fuel cell (PEMFC) is among the most efficient energy conversion devices for future transportation applications. The PEMFC is operated through the electrochemical hydrogen oxidation reaction (HOR) at the anode and oxygen reduction reaction (ORR) at the cathode. The ORR generally faces higher kinetic barrier than HOR and therefore requires more catalyst. At present, the electrocatalysts of choice are precious metals, such as platinum supported on a carbon substrate. High costs and limited reserves of the precious metals pose a major challenge for large scale commercialization of PEMFCs. Non-precious-metal catalysts (NPMCs) made of Fe and Co in carbon composites have attracted a great deal of attentions since they were discovered with promising activities towards ORR in acidic media. Their activities in alkaline or neutral media were also extensively studied, although the subject is beyond the scope of the current discussion. Extensive characterizations have been carried out in attempts to understand the roles of transition metals, nitrogen, and surface properties in the catalytic activity of these NPMCs. The durability of these NPMCs in the protonic medium has been a major concern, although recent work by Wu et al. demonstrated a catalyst with improved stability in the PEMFC operating environment. At present, the catalytic activities of NPMCs are still significantly less than that of precious metals. To make NPMCs truly competitive, substantial improvements in two critical properties have to be accomplished: 1) a higher turnover frequency (TOF) per active site; and 2) a greater catalytic site density per unit volume. To improve TOF requires an in-depth understanding of the influences by transition metals, organic ligands, and the support on the active site. The interdependences between these factors are still under intensive investigation. To improve active site density, a NPMC precursor with densely populated metal– ligand sites and high surface exposure, and preferably free of inactive support, such as carbon, would be a rational starting point. For example, the volumetric current density of NPMCs prepared by impregnating transition metal salt over porous carbon appeared to have reached an upper limit, although performances were recently elevated through pore filler and pore former approaches. 7] More recently, NPMCs prepared using the metal–organic frameworks (MOFs) as precursors have generated excellent catalytic performances. In MOFs, the frameworks are built through the metal–ligand interaction with well-defined coordination chemistry and the highest possible precursor site density. One key issue with MOFbased NPMC preparation is the removal of the high level of metal, which is currently accomplished by either high-temperature vaporization during the thermolysis or an acid wash after heat treatment. In either approach, limitations on the experimental conditions affected the versatility of the method. Herein we describe a new approach of preparing highly active NPMCs using porous organic polymer (POP) precursors containing densely populated transition-metal–nitrogen coordination sites uniformly decorated over the micropore surface. POPs have recently emerged as a new class of gasstorage and separation materials. A broad selection of monomers and cross-linking reactions provide great flexibility for producing very-high-surface-area POPs containing different functional groups. When nitrogen-containing macrocyclic functional groups, such as porphyrin or phthalocyanine, are employed as the oligomers for the synthesis, the new [*] Dr. S. Yuan, Dr. J. Shui, C. Chen, S. Commet, B. Reprogle, Dr. D.-J. Liu Chemical Sciences & Engineering Division Argonne National Laboratory, Argonne, IL 60439 (USA) E-mail: djliu@anl.gov

Facile Oxidative Conversion of TiH2 to High-Concentration Ti3+-Self-Doped Rutile TiO2 with Visible-Light Photoactivity

TiO2, in the rutile phase with a high concentration of self-doped Ti(3+), has been synthesized via a facile, all inorganic-based, and scalable method of oxidizing TiH2 in H2O2 followed by calcinations in Ar gas. The material was shown to be photoactive in the visible-region of the electromagnetic spectrum. Powdered X-ray diffraction (PXRD), transmission electron microscopy (TEM), ultraviolet-visible-near-infrared (UV-vis-NIR), diffuse reflectance spectroscopy (DRS), and Brunauer-Emmett-Teller (BET) methods were used to characterize the crystalline, structural, and optical properties and specific surface area of the as-synthesized Ti(3+)-doped rutile, respectively. The concentration of Ti(3+) was quantitatively studied by electron paramagnetic resonance (EPR) to be as high as one Ti(3+) per ~4300 Ti(4+). Furthermore, methylene blue (MB) solution and an industry wastewater sample were used to examine the photocatalytic activity of the Ti(3+)-doped TiO2 which was analyzed by UV-vis absorption, Fourier transform infrared spectroscopy (FT-IR), and electrospray ionization mass spectrometry (ESI-MS). In comparison to pristine anatase TiO2, our Ti(3+) self-doped rutile sample exhibited remarkably enhanced visible-light photocatalytic degradation on organic pollutants in water.

Three-dimensional conducting oxide nanoarchitectures: morphology-controllable synthesis, characterization, and applications in lithium-ion batteries

We report the synthesis, characterization and applications in Li-ion batteries of a set of 3-dimensional (3-D) nanostructured conducting oxides including fluorinated tin oxide (FTO) and aluminum zinc oxide (AZO). The morphology of these 3-D conducting oxide nanoarchitectures can be directed towards either mono-dispersed hollow nanobead matrix or mono-dispersed sponge-like nanoporous matrix by controlling the surface charge of the templating polystyrene (PS) nanobeads, the steric hindrance and hydrolysis rates of the precursors, pH of the solvents etc. during the evaporative co-assembly of the PS beads. These 3-D nanostructured conducting oxide matrices possess high surface area (over 100 m(2) g(-1)) and accessible interconnected pores extending in all three spatial dimensions. By optimizing the temperature profile during calcination, we can obtain large area (of a few cm(2)) and crack-free nanoarchitectured films with thickness over 60 μm. As such, the sheet resistance of these nanoarchitectured films on FTO glass can reach below 20 Ω per square. The nanoarchitectured FTO electrodes were used as anodes in Li-ion batteries, and they showed an enhanced cycling performance and stability over pure SnO2.

Visible-light photocatalytic SiO2/TiO2−xCx/C nanoporous composites using TiCl4 as the precursor for TiO2 and polyhydroxyl tannin as the carbon source

We report an architecturally controlled synthesis of SiO2/TiO2−xCx/C nanoporous composites that exhibit high absorption capability and efficient visible-light photocatalytic activity. The nanoporous composites are composed of silica particles as the cores and TiCl4 as the precursor for the TiO2 shell. Tannin is used as the binding agent between the core and the precursor shell, the carbon source, and the porosity promoter. The structure, crystallinity, morphology, and other physical–chemical properties of the samples are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microcopy (HRTEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption isotherm measurements, UV–vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL). The chemical contents of the SiO2/TiO2−xCx/C nanoporous composites were also analyzed by energy dispersive X-ray spectra (EDX). The formation mechanism of the nanoporous composites was extensively discussed. Methylene blue (MB) solutions were used as model wastewater to evaluate the adsorption and photocatalytic activity of the samples under natural sunlight and visible light. Fourier transform-infrared spectroscopy (FT-IR) and mass spectrometry (MS) were used to investigate the photodegradated species on the photocatalysts and in solution, respectively. The SiO2/TiO2−xCx/C nanoporous composite samples exhibit remarkably enhanced visible-light photoactivity than Degussa P25 and pure TiO2, and can be readily collected for reuse by gravitational sedimentation.