Andrew B. Bocarsly

Ni–Al Films on Glassy Carbon Electrodes Generate an Array of Oxygenated Organics from CO2

Co-reporter:Aubrey R. Paris and Andrew B. Bocarsly

ACS Catalysis October 6, 2017 Volume 7(Issue 10) pp:6815-6815

Publication Date(Web):September 11, 2017

DOI:10.1021/acscatal.7b02146

The transformation of CO2 into chemical feedstocks or fuels is an attractive goal, but catalysts capable of generating useful, multicarbon products have been challenging to design. Here, thin films of the intermetallic Ni3Al on glassy carbon are found to be electrocatalytic for aqueous CO2 reduction. At–1.38 V vs Ag/AgCl, Ni3Al films produce a range of C1, C2, and C3 oxygenated organic species including 1-propanol and methanol at Faradaic efficiencies that are competitive with single-metal electrodes reported in the literature. To the best of our knowledge, Ni3Al on glassy carbon is the only noncopper-containing material shown to generate C3 products.Keywords: 1-propanol; C3 production; CO2 reduction; electrocatalysis; methanol; Ni3Al; nickel aluminum; thin film;

The effect of Mg-doping and Cu nonstoichiometry on the photoelectrochemical response of CuFeO2

Co-reporter:Anna Wuttig;Jason W. Krizan;Jing Gu;Jessica J. Frick;Robert J. Cava

Journal of Materials Chemistry A 2017 vol. 5(Issue 1) pp:165-171

Publication Date(Web):2016/12/20

DOI:10.1039/C6TA06504J

We report the tuning of CuFeO2 photoelectrodes by Mg doping and Cu deficiency to demonstrate the effects of carrier concentration on the photoresponse. Carrier type and concentration were quantitatively assessed using the Hall effect on pure, Mg-incorporated, and Cu-deficient pellets (CuFe1−xMgxO2 and Cu1−yFeO2, x = 0, 0.0005, 0.005, 0.02, and y = 0.005, 0.02) over the range of thermodynamic stability achievable using solid-state synthesis. The same samples were used in a photoelectrochemical cell to measure their photoresponse. We find that the material with the lowest p-type carrier concentration and the highest carrier mobility shows the largest photoresponse. Furthermore, we show that increasing the p-type carrier concentration and thus the conductivity to high levels is limited by the delafossite defect chemistry, which changes the majority carrier type from p-type to n-type near the Mg solubility limit (x = 0.05) and at high Cu defect concentrations.

Probing the Mechanism of Aqueous CO2 Reduction on Post-Transition-Metal Electrodes using ATR-IR Spectroelectrochemistry

Co-reporter:James E. Pander III, Maor F. Baruch, and Andrew B. Bocarsly

ACS Catalysis 2016 Volume 6(Issue 11) pp:7824

Publication Date(Web):October 10, 2016

DOI:10.1021/acscatal.6b01879

The role of metastable surface oxides in the reduction of CO2 on lead, bismuth, tin, and indium electrodes was probed using in situ attenuated total reflectance infrared (ATR-IR) spectroelectrochemistry. The effect of the surface oxide on the Faradaic efficiency of CO2 reduction to formic acid was studied by etching and anodizing the electrodes, and the results were correlated with respect to the observed spectroscopic behavior of the catalysts. A metastable oxide is observed on lead, tin, and indium cathodes under the electrochemical conditions necessary for CO2 reduction. Spectroscopic evidence suggests that bismuth electrodes are fully reduced to the metal under the same conditions. The dynamics of the electroreduction of CO2 at lead and bismuth electrodes appears to be different from that on on tin and indium electrodes, which suggests that these catalysts act through different mechanistic pathways. The post-transition-metal block can be divided into three classes of materials: oxide-active materials, oxide-buffered materials, and oxide-independent materials, and the mechanistic differences are discussed.Keywords: CO2 reduction; CO2 utilization; electrocatalysis; in situ IR spectroscopy; p-block metals; spectroelectrochemistry

Light-Driven Heterogeneous Reduction of Carbon Dioxide: Photocatalysts and Photoelectrodes

Co-reporter:James L. White, Maor F. Baruch, James E. Pander III, Yuan Hu, Ivy C. Fortmeyer, James Eujin Park, Tao Zhang, Kuo Liao, Jing Gu, Yong Yan, Travis W. Shaw, Esta Abelev, and Andrew B. Bocarsly

Chemical Reviews 2015 Volume 115(Issue 23) pp:12888

Publication Date(Web):October 7, 2015

DOI:10.1021/acs.chemrev.5b00370

Mechanistic Insights into the Reduction of CO2 on Tin Electrodes using in Situ ATR-IR Spectroscopy

Co-reporter:Maor F. Baruch, James E. Pander III, James L. White, and Andrew B. Bocarsly

ACS Catalysis 2015 Volume 5(Issue 5) pp:3148

Publication Date(Web):April 13, 2015

DOI:10.1021/acscatal.5b00402

The reduction of CO2 on tin cathodes was studied using in situ attenuated total reflectance infrared spectroscopy (ATR-IR). Thin films of a mixed Sn/SnOx species were deposited onto a single-crystal ZnSe ATR crystal. Peaks centered at about 1500, 1385, and 1100 cm–1, attributed to a surface-bound monodentate tin carbonate species, were consistently present under conditions at which CO2 reduction takes place. It was shown that these peaks are only present at potentials where CO2 reduction is observed. Moreover, these peaks disappear if the pH of the reaction is too low or if the tin surface is chemically etched to remove surface oxide. Sn6O4(OH)4 and SnO2 nanoparticles were shown to be catalytically active for CO2 reduction, and insights into the oxidation state of the catalytically active species are gained from a comparison of the catalytic behavior of the two nanoparticle species. From these experiments, a mechanism governing the reduction of CO2 on tin electrodes is proposed.Keywords: carbon dioxide reduction; IR spectroelectrochemistry; tin electrochemistry; tin oxide nanoparticles; tin oxides

Design of a Catalytic Active Site for Electrochemical CO2 Reduction with Mn(I)-Tricarbonyl Species

Co-reporter:Jay Agarwal, Travis W. Shaw, Henry F. Schaefer III, and Andrew B. Bocarsly

Inorganic Chemistry 2015 Volume 54(Issue 11) pp:5285-5294

Publication Date(Web):May 13, 2015

DOI:10.1021/acs.inorgchem.5b00233

The design, synthesis, and assessment of a new manganese-centered catalyst for the electrochemical reduction of CO2 is described. The reported species, MnBr(6-(2-hydroxyphenol)-2,2′-bipyridine)(CO)3, includes a ligand framework with a phenolic proton in close proximity to the CO2 binding site, which allows for facile proton-assisted C–O bond cleavage. As a result of this modification, seven times the electrocatalytic current enhancement is observed compared to MnBr(2,2′-bipyridine)(CO)3. Moreover, reduction is possible at only 440 mV of overpotential. Theoretical computations suggest that the entropic contribution to the activation free energy is partially responsible for the increased catalytic activity. Experimental work, including voltammetry and product quantification from controlled potential electrolysis, suggests a key mechanistic role for the phenolic proton in the conversion of CO2 to CO.

Electrochemical Reduction of Aqueous Imidazolium on Pt(111) by Proton Coupled Electron Transfer

Co-reporter:Kuo Liao;Mikhail Askerka;Elizabeth L. Zeitler

Topics in Catalysis 2015 Volume 58( Issue 1) pp:23-29

Publication Date(Web):2015 February

DOI:10.1007/s11244-014-0340-2

Recent electrochemical studies have reported aqueous CO2 reduction to formic acid, formaldehyde and methanol at potentials of ca. −600 mV versus SCE, when using a Pt working electrode in acidic pyridine solutions. In those experiments, pyridinium is thought to function as a one-electron shuttle for the underlying multielectron reduction of CO2. DFT studies proposed that the critical step of the underlying reaction mechanism is the one-electron reduction of pyridinium at the Pt surface through proton coupled electron transfer. Such reaction forms a H adsorbate that is subsequently transferred to CO2 as a hydride, through a proton coupled hydride transfer mechanism where pyridinium functions as a Brønsted acid. Here, we find that imidazolium exhibits an electrochemical behavior analogous to pyridinium, as characterized by the experimental and theoretical analysis of the initial reduction on Pt. A cathodic wave, with a cyclic voltammetric half wave potential of ca. −680 mV versus SCE, is consistent with the theoretical prediction based on the recently proposed reaction mechanism suggesting that positively charged Brønsted acids could serve as electrocatalytic one-electron shuttle species for multielectron CO2 reduction.

Substituent Effects in the Pyridinium Catalyzed Reduction of CO2 to Methanol: Further Mechanistic Insights

Co-reporter:Emily E. Barton Cole;Maor F. Baruch;Robert P. L’Esperance

Topics in Catalysis 2015 Volume 58( Issue 1) pp:15-22

Publication Date(Web):2015 February

DOI:10.1007/s11244-014-0343-z

A series of substituted pyridiniums were examined for their catalytic ability to electrochemically reduce carbon dioxide to methanol. It is found that in general increased basicity of the nitrogen of the amine and higher LUMO energy of the pyridinium correlate with enhanced carbon dioxide reduction. The highest faradaic yield for methanol production at a platinum electrode was 39 ± 4 % for 4-aminopyridine compared to 22 ± 2 % for pyridine. However, 4-tertbutyl and 4-dimethylamino pyridine showed decreased catalytic behavior, contrary to the enhanced activity associated with the increased basicity and LUMO energy, and suggesting that steric effects also play a significant role in the behavior of pyridinium electrocatalysts. Mechanistic models for the the reaction of the pyridinium with carbon dioxide are considered.

Direct Reduction of Carbon Dioxide to Formate in High-Gas-Capacity Ionic Liquids at Post-Transition-Metal Electrodes

Co-reporter:Dr. John D. Watkins ; Andrew B. Bocarsly

ChemSusChem 2014 Volume 7( Issue 1) pp:284-290

Publication Date(Web):

DOI:10.1002/cssc.201300659

Abstract

As an approach to combat the increasing emissions of carbon dioxide in the last 50 years, the sequestration of carbon dioxide gas in ionic liquids has become an attractive research area. Ionic liquids can be made that possess incredibly high molar absorption and specificity characteristics for carbon dioxide. Their high carbon dioxide solubility and specificity combined with their high inherent electrical conductivity also creates an ideal medium for the electrochemical reduction of carbon dioxide. Herein, a lesser studied ionic liquid, 1-ethyl-3-methylimidazolium trifluoroacetate, was used as both an effective carbon dioxide capture material and subsequently as an electrochemical matrix with water for the direct reduction of carbon dioxide into formate at indium, tin, and lead electrodes in good yield (ca. 3 mg h⁻¹ cm⁻²).

Anodized Indium Metal Electrodes for Enhanced Carbon Dioxide Reduction in Aqueous Electrolyte

Co-reporter:Zachary M. Detweiler, James L. White, Steven L. Bernasek, and Andrew B. Bocarsly

Langmuir 2014 Volume 30(Issue 25) pp:7593-7600

Publication Date(Web):2017-2-22

DOI:10.1021/la501245p

The interactions of CO2 with indium metal electrodes have been characterized for electrochemical formate production. The electrode oxidation state, morphology, and voltammetric behaviors were systematically probed. It was found that an anodized indium electrode stabilized formate production over time compared to etched indium electrodes and indium electrodes bearing a native oxide in applied potential range of −1.4 to −1.8 V vs SCE. In addition, it was observed that formate is the major product at unprecedentedly low overpotentials at the anodized surface. A surface hydroxide species was observed suggesting a mechanism of formate production that involves insertion of CO2 at the indium interface to form an electroactive surface bicarbonate species.

Electrochemistry of Aqueous Pyridinium: Exploration of a Key Aspect of Electrocatalytic Reduction of CO2 to Methanol

Co-reporter:Yong Yan ; Elizabeth L. Zeitler ; Jing Gu ; Yuan Hu

Journal of the American Chemical Society 2013 Volume 135(Issue 38) pp:14020-14023

Publication Date(Web):August 23, 2013

DOI:10.1021/ja4064052

The mechanism by which pyridinium (pyrH+) is reduced at a Pt electrode is a matter of recent controversy. The quasireversible cyclic voltammetric wave observed at −0.58 V vs SCE at a Pt electrode was originally proposed to correspond to reduction of pyrH+ to pyridinyl radical (pyrH•). This mechanistic explanation for the observed electrochemistry seems unlikely in light of recent quantum mechanical calculations that predict a very negative reduction potential (−1.37 V vs SCE) for the formation of pyrH•. Several other mechanisms have been proposed to account for the discrepancy in calculated and observed reduction potentials, including surface adsorption of pyrH•, reduction of pyrH+ by two electrons rather than one, and reduction of the pyrH+ proton to a surface hydride rather than a π-based radical product. This final mechanism, which can be described as inner-sphere reduction of pyrH+ to form a surface hydride, is consistent with experimental observations.

p-Type CuRhO2 as a Self-Healing Photoelectrode for Water Reduction under Visible Light

Co-reporter:Jing Gu ; Yong Yan ; Jason W. Krizan ; Quinn D. Gibson ; Zachary M. Detweiler ; Robert J. Cava

Journal of the American Chemical Society 2013 Volume 136(Issue 3) pp:830-833

Publication Date(Web):December 30, 2013

DOI:10.1021/ja408876k

Polycrystalline CuRhO2 is investigated as a photocathode for the splitting of water under visible irradiation. The band edge positions of this material straddle the water oxidation and reduction redox potentials. Thus, photogenerated conduction band electrons are sufficiently energetic to reduce water, while the associated valence band holes are energetically able to oxidize water to O2. Under visible illumination, H2 production is observed with ∼0.2 V underpotential in an air-saturated solution. In contrast, H2 production in an Ar-saturated solution was found to be unstable. This instability is associated with the reduction of the semiconductor forming Cu(s). However, in the presence of air or O2, bulk Cu(s) was not detected, implying that CuRhO2 is self-healing when air is present. This property allows for the stable formation of H2 with ca. 80% Faradaic efficiency.

Mg-Doped CuFeO2 Photocathodes for Photoelectrochemical Reduction of Carbon Dioxide

Co-reporter:Jing Gu, Anna Wuttig, Jason W. Krizan, Yuan Hu, Zachary M. Detweiler, Robert J. Cava, and Andrew B. Bocarsly

The Journal of Physical Chemistry C 2013 Volume 117(Issue 24) pp:12415-12422

Publication Date(Web):May 22, 2013

DOI:10.1021/jp402007z

Mg-doped CuFeO2 delafossite is reported to be photoelectrochemically active for CO2 reduction. The material was prepared via conventional solid-state methods, and subsequently assembled into an electrode as a pressed pellet. Addition of a Mg2+ dopant is found to substantially improve the conductivity of the material, with 0.05% Mg-doped CuFeO2 electrodes displaying photocathodic currents under visible irradiation. Photocurrent is found to onset at irradiation wavelengths of ∼800 nm with the incident photon-to-current efficiency reaching a value of 14% at 340 nm using an applied electrode potential of −0.4 V vs SCE. Photoelectrodes were determined to have a −1.1 V vs SCE conduction band edge and were found capable of the reduction of CO2 to formate at 400 mV of underpotential. The conversion efficiency is maximized at −0.9 V vs SCE, with H2 production contributing as a considerable side reaction. These results highlight the potential to produce Mg-doped p-type metal oxide photocathodes with a band structure tuned to optimize CO2 reduction.

Comparative Study of Imidazole and Pyridine Catalyzed Reduction of Carbon Dioxide at Illuminated Iron Pyrite Electrodes

Co-reporter:Andrew B. Bocarsly, Quinn D. Gibson, Amanda J. Morris, Robert P. L’Esperance, Zachary M. Detweiler, Prasad S. Lakkaraju, Elizabeth L. Zeitler, and Travis W. Shaw

ACS Catalysis 2012 Volume 2(Issue 8) pp:1684

Publication Date(Web):July 3, 2012

DOI:10.1021/cs300267y

The chemistry of the electrocatalytic reduction of CO2 using nitrogen containing heteroaromatics is further explored by the direct comparison of imidazole and pyridine catalyzed CO2 reduction at illuminated iron pyrite electrodes. The mechanism of imidazole based catalysis of CO2 reduction is investigated by analyzing the catalytic activity of a series of imidazole derivatives using cyclic voltammetry. While similar product distributions are obtained for both imidazole and pyridine, the imidazole catalyzed reduction of CO2 likely proceeds via a very different mechanism involving the C2 carbon of the imidazole ring.Keywords: aromatic amine electrocatalysts; carbon dioxide reduction; formic acid production; imidazolium based electrocatalyst; iron pyrite photocathodes; photoelectrochemistry; pyridinium based electrocatalysis;

Electrocatalytic Carbon Dioxide Activation: The Rate-Determining Step of Pyridinium-Catalyzed CO2 Reduction

Co-reporter:Dr. Ama J. Morris;Robert T. McGibbon ; Andrew B. Bocarsly

ChemSusChem 2011 Volume 4( Issue 2) pp:191-196

Publication Date(Web):

DOI:10.1002/cssc.201000379

Abstract

The reactivity of reduced pyridinium with CO₂ was investigated as a function of catalyst concentration, temperature, and pressure at platinum electrodes. Concentration experiments show that the catalytic current measured by cyclic voltammetry increases linearly with pyridinium and CO₂ concentrations; this indicates that the rate-determining step is first order in both. The formation of a carbamate intermediate is supported by the data presented. Increased electron density at the pyridyl nitrogen upon reduction, as calculated by DFT, favors a Lewis acid/base interaction between the nitrogen and the CO₂. The rate of the known side reaction, pyridinium coupling to form hydrogen, does not vary over the temperature range investigated and had a rate constant of 2.5 M⁻¹ s⁻¹. CO₂ reduction followed Arrhenius behavior and the activation energy determined by electrochemical simulation was (69±10) kJ mol⁻¹.

Using a One-Electron Shuttle for the Multielectron Reduction of CO2 to Methanol: Kinetic, Mechanistic, and Structural Insights

Co-reporter:Emily Barton Cole ; Prasad S. Lakkaraju ; David M. Rampulla ; Amanda J. Morris ; Esta Abelev

Journal of the American Chemical Society 2010 Volume 132(Issue 33) pp:11539-11551

Publication Date(Web):July 28, 2010

DOI:10.1021/ja1023496

Pyridinium and its substituted derivatives are effective and stable homogeneous electrocatalysts for the aqueous multiple-electron, multiple-proton reduction of carbon dioxide to products such as formic acid, formaldehyde, and methanol. Importantly, high faradaic yields for methanol have been observed in both electrochemical and photoelectrochemical systems at low reaction overpotentials. Herein, we report the detailed mechanism of pyridinium-catalyzed CO2 reduction to methanol. At metal electrodes, formic acid and formaldehyde were observed to be intermediate products along the pathway to the 6e−-reduced product of methanol, with the pyridinium radical playing a role in the reduction of both intermediate products. It has previously been thought that metal-derived multielectron transfer was necessary to achieve highly reduced products such as methanol. Surprisingly, this simple organic molecule is found to be capable of reducing many different chemical species en route to methanol through six sequential electron transfers instead of metal-based multielectron transfer. We show evidence for the mechanism of the reduction proceeding through various coordinative interactions between the pyridinium radical and carbon dioxide, formaldehyde, and related species. This suggests an inner-sphere-type electron transfer from the pyridinium radical to the substrate for various mechanistic steps where the pyridinium radical covalently binds to intermediates and radical species. These mechanistic insights should aid the development of more efficient and selective catalysts for the reduction of carbon dioxide to the desired products.

Stabilizing cyanosols: amorphous cyanide bridged transition metal polymer nanoparticles

Co-reporter:Christine M. Burgess, Nan Yao and Andrew B. Bocarsly

Journal of Materials Chemistry A 2009 vol. 19(Issue 46) pp:8846-8855

Publication Date(Web):15 Oct 2009

DOI:10.1039/B911682F

Nanoparticles of an amorphous, cyanide bridged, transition metal polymer are isolated by exchanging the counter-ions of the polymer network with cetyltrimethylammonium (CTA+). The nanoparticles isolated are stable, soluble in organic solvents such as dichloromethane and have an average diameter of 4 ± 1 nm (mean ± std). The reported technique is amenable to a variety of transition metals as Pd–Co, Pd–Ru and Pd–Fe cyanometalate polymer nanoparticles are isolated. Increasing the reaction time prior to counter-ion exchange allows for the isolation of nanoparticle agglomerates. The transition metal ratio of the nanoparticulate polymer network is demonstrated to be under synthetic control. Subsequent chemical alteration of the nanoparticles is afforded due to the free coordination sites of the transition metals in the polymer. The nanoparticles also serve as chemical precursors to transition metal alloy nanoparticles due to the ability of bridging cyanides to act as reducing agents at relatively low temperatures.

A versatile chemical method for the formation of macroporous transition metal alloys from cyanometalate coordination polymers

Co-reporter:Christine M. Burgess, Martina Vondrova and Andrew B. Bocarsly

Journal of Materials Chemistry A 2008 vol. 18(Issue 31) pp:3694-3701

Publication Date(Web):04 Jul 2008

DOI:10.1039/B804258F

A facile two-step synthetic route to macroporous metal and metal alloy frameworks from hydrogel-forming coordination polymers known as cyanogels is described. The polymerization of a chlorometalate and cyanometalate in aqueous solution results in the formation of a cyanogel that will auto-reduce at elevated temperatures to form metal alloys under an inert atmosphere. Cyanogels are versatile precursors to macroporous metals due to the large number of metal alloy systems that can be produced. This synthetic route is advantageous due to the production of uncontaminated final products of refractory metals at low temperatures. Transient reactive liquid sintering is shown to be the physical process through which macroporous metal forms from the cyanogel precursor.

Investigation of PEMFC operation above 100 °C employing perfluorosulfonic acid silicon oxide composite membranes

Co-reporter:K.T Adjemian, S Srinivasan, J Benziger, A.B Bocarsly

Journal of Power Sources 2002 Volume 109(Issue 2) pp:356-364

Publication Date(Web):1 July 2002

DOI:10.1016/S0378-7753(02)00086-1

Various perfluorosulfonic acid membranes (PFSAs) were studied as pure and silicon oxide composite membranes for operation in hydrogen/oxygen proton-exchange membrane fuel cells (PEMFCs) from 80 to 140 °C. The composite membranes were prepared either by impregnation of pre-formed PFSAs via sol–gel processing of a polymeric silicon oxide, recasting a film using solubilized PFSAs and a silicon oxide polymer/gel. All composite membranes had a silicon oxide content of less than or equal to 10% by weight. Decreasing the equivalent weight and thickness of the PFSAs, in addition to the incorporation of silicon oxide helped improve water management in a PEMFC at elevated temperatures. Fourier transform-infrared spectroscopy–attenuated total reflectance (FT-IR–ATR), and scanning electron microscopy (SEM) experiments indicated an evenly distributed siloxane polymer in all of the composite membranes. At a potential of 0.4 V the Aciplex 1004/silicon oxide composite membrane in a humidified H2/O2 PEMFC at 130 °C and a pressure of 3 atm delivered six times higher current density than unmodified Nafion 115 under the same conditions, and 1.73 times the current density when unmodified Nafion 115 was operated with humidified gases at 80 °C and 1 atm of pressure. Furthermore, the PEMFC performances with the PFSA/silicon oxide composite membranes were physically more robust than the control membranes (unmodified PFSAs), which degraded after high operation temperature and thermal cycling.

Photons to formate: Efficient electrochemical solar energy conversion via reduction of carbon dioxide

Co-reporter:James L. White, Jake T. Herb, Jerry J. Kaczur, Paul W. Majsztrik, Andrew B. Bocarsly

Journal of CO2 Utilization (September 2014) Volume 7() pp:1-5

Publication Date(Web):1 September 2014

DOI:10.1016/j.jcou.2014.05.002

•CO2 was reduced to formate using an integrated silicon PV electrolyzer system.•The flow electrolyzer design utilized an indium cathode and an IrO2 anode.•3 cells with 109 cm2 electrodes were placed in series forming an electrolyzer stack.•Thermionic energy conversion efficiency (η) using sunlight (AM1.5) was 1.8%.•This represents the highest η for solar CO2 reduction reported to date.The storage of solar energy as formic acid generated electrochemically from carbon dioxide has been identified as a viable solar fuel pathway. We report that this transformation can be accomplished by separating light absorption and CO2 reduction through the use of a commercial solar panel illuminated with natural AM1.5 sunlight to power a custom closed-loop electrochemical flow cell stack. Faradaic yields for formate of up to 67% have been demonstrated in this system, yielding a solar energy to fuel thermionic conversion efficiency above 1.8%.Download full-size image

A versatile chemical method for the formation of macroporous transition metal alloys from cyanometalate coordination polymers

Co-reporter:Christine M. Burgess, Martina Vondrova and Andrew B. Bocarsly

Journal of Materials Chemistry A 2008 - vol. 18(Issue 31) pp:NaN3701-3701

Publication Date(Web):2008/07/04

DOI:10.1039/B804258F

A facile two-step synthetic route to macroporous metal and metal alloy frameworks from hydrogel-forming coordination polymers known as cyanogels is described. The polymerization of a chlorometalate and cyanometalate in aqueous solution results in the formation of a cyanogel that will auto-reduce at elevated temperatures to form metal alloys under an inert atmosphere. Cyanogels are versatile precursors to macroporous metals due to the large number of metal alloy systems that can be produced. This synthetic route is advantageous due to the production of uncontaminated final products of refractory metals at low temperatures. Transient reactive liquid sintering is shown to be the physical process through which macroporous metal forms from the cyanogel precursor.

Stabilizing cyanosols: amorphous cyanide bridged transition metal polymer nanoparticles

Co-reporter:Christine M. Burgess, Nan Yao and Andrew B. Bocarsly

Journal of Materials Chemistry A 2009 - vol. 19(Issue 46) pp:NaN8855-8855

Publication Date(Web):2009/10/15

DOI:10.1039/B911682F

Nanoparticles of an amorphous, cyanide bridged, transition metal polymer are isolated by exchanging the counter-ions of the polymer network with cetyltrimethylammonium (CTA+). The nanoparticles isolated are stable, soluble in organic solvents such as dichloromethane and have an average diameter of 4 ± 1 nm (mean ± std). The reported technique is amenable to a variety of transition metals as Pd–Co, Pd–Ru and Pd–Fe cyanometalate polymer nanoparticles are isolated. Increasing the reaction time prior to counter-ion exchange allows for the isolation of nanoparticle agglomerates. The transition metal ratio of the nanoparticulate polymer network is demonstrated to be under synthetic control. Subsequent chemical alteration of the nanoparticles is afforded due to the free coordination sites of the transition metals in the polymer. The nanoparticles also serve as chemical precursors to transition metal alloy nanoparticles due to the ability of bridging cyanides to act as reducing agents at relatively low temperatures.

The effect of Mg-doping and Cu nonstoichiometry on the photoelectrochemical response of CuFeO2

Co-reporter:Anna Wuttig, Jason W. Krizan, Jing Gu, Jessica J. Frick, Robert J. Cava and Andrew B. Bocarsly

Journal of Materials Chemistry A 2017 - vol. 5(Issue 1) pp:NaN171-171

Publication Date(Web):2016/11/14

DOI:10.1039/C6TA06504J

We report the tuning of CuFeO2 photoelectrodes by Mg doping and Cu deficiency to demonstrate the effects of carrier concentration on the photoresponse. Carrier type and concentration were quantitatively assessed using the Hall effect on pure, Mg-incorporated, and Cu-deficient pellets (CuFe1−xMgxO2 and Cu1−yFeO2, x = 0, 0.0005, 0.005, 0.02, and y = 0.005, 0.02) over the range of thermodynamic stability achievable using solid-state synthesis. The same samples were used in a photoelectrochemical cell to measure their photoresponse. We find that the material with the lowest p-type carrier concentration and the highest carrier mobility shows the largest photoresponse. Furthermore, we show that increasing the p-type carrier concentration and thus the conductivity to high levels is limited by the delafossite defect chemistry, which changes the majority carrier type from p-type to n-type near the Mg solubility limit (x = 0.05) and at high Cu defect concentrations.