bluuebunny/crossref_metadata_2025_split huggingface dataset:
CO2 Electrocatalytic Reduction at Gold and Copper Electrodes: Role of Particle Size and Surface Chemistry
Authors: Andrews Evan Michael , Flake John , Fang Yuxin 
Published: February 2020

Electrochemical CO2 reduction holds the potential to produce energy-dense liquid fuels using renewable energy sources. Previous works have shown that Cu provides some of the highest yields for valuable products such as methane or ethylene, yet the mechanisms for selectivity are not well understood. Of course, nature performs similar reactions using enzymes including nanocluster metal alloys and ligands with extraordinary selectivity. Here we discuss the effects of various ligands at Cu, Au and Au-Cu alloy electrocatalysts.
From the literature, results of CO2 electroreduction on bulk Cu, Au and Au-Cu alloys are known (1-3) as are the size effects of Cu and Au nanoparticles (4, 5), but the effect of chemical surface modification is still unknown, as is the size effect of gold/copper alloy nanoparticles.
In this work we demonstrate the effect of chemical surface modification and the size effect of Au-Cu alloy nanoparticles with the aim of combining the two effects to improve CO conversion and hydrogenation. The effect of surface chemistry is studied using planar electrodes modified by organic compounds. Copper and gold foils are exposed to strongly adsorbed ligands such as alkylthiols and glutathione (GSH) and subsequently used as electrocatalysts. As shown in Figure 1, where copper foil was modified with GSH, the adsorbed ligands strongly affect the product yields and selectivity. At the optimal CO yield potential, the yield of CO on the GSH-modified copper was 2.4 times that of blank bulk copper. Although the yield of CH4 has been decreased by a factor of 0.5 in exchange, the overall yield of gas product has been increased by a factor of 2 on the surface engineered electrode.
The size effect of Au-Cu nanoparticles is investigated using nanoparticles synthesized via the Brust-Schiffrin method immobilized in various binder inks as electrocatalysts for CO2reduction. Ultimately, we consider the potential to break scaling relationships associated with conventional metal electrodes through the use of size control, alloys and ligands.
References
1. Y. Hori, A. Murata, K. Kikuchi and S. Suzuki, J. Chem. Soc., Chem. Commun., 728 (1987).
2. Y. Hori, K. Kikuchi and S. Suzuki, Chemistry Letters, 1695 (1985).
3. J. Christophe, T. Doneux and C. Buess-Herman, Electrocatalysis, 3, 139 (2012).
4. D. R. Kauffman, D. Alfonso, C. Matranga, H. Qian and R. Jin, Journal of the American Chemical Society, 134, 10237 (2012).
5. R. Reske, H. Mistry, F. Behafarid, B. Roldan Cuenya and P. Strasser, Journal of the American Chemical Society (2014).

Figure 1
Enhancing the Electrochemical Surface Area of Tin Based Porous Electrodes for Carbon Dioxide Reduction to Formate
Authors: Agarwal Arun S , Gautam Dushyant , Rode Edward , Jasinski Jacek B , Nguyen Tu Quang , Sunkara Mahendra Kumar , Sridhar Narasi 
Published: February 2020

Conversion of CO2 to value added chemicals can provide an attractive alternate pathway for making petrochemicals without petroleum based raw materials, storing renewable energy in chemical form, as well as providing greater acceptance to CO2 as a valuable resource of chemical manufacture. This work deals with the electrochemical reduction of CO2 to formate / formic acid, with specific focus on economic feasibility of this process. The current density or rate of production of product directly affects the overall capital expenditure of a large scale process by affecting the reactor requirements. In this paper, the various approaches studied to enhance the electrochemical surface area of the electrodes will be presented. Electroplating of tin of carbon fiber substrates provided a 5-10 times area enhancement. Nano particles of tin (~ 5 nm size) were formed on high surface area activated carbon black (Vulcan XC-72). The porous electrode structure is optimized based on the binder content and loading on the base substrate. Studies were also performed to ascertain the effects of tin oxide on the reduction of CO2 to the desired product. The time evolution of the performance of such electrodes with respect to both, the overall current density as well as the selectivity towards formate product will be presented. Characterization of the electrode and particle morphology based on ‘before’ and ‘after’ experiment SEM and TEM analysis will also be presented.
Effect of Acid-Leaching on the Electrochemical Performance of Carbon-Supported Copper Phthalocyanine Tetrasulfonic Acid Tetrasodium Salt (CuTSPc/C) Catalys
Authors: Qiao Jinli , Qing Xin 
Published: February 2020

Since the strong O=O bond (498kJ mol-1) with very slow oxygen reduction reaction (ORR) rate at the cathode has a much larger overpotential (or polarization) than that of hydrogen oxidation reaction (HOR) at the anode, the cathodic ORR has become the most challenging step in a fuel cell1. Up to now, Pt is still the best catalyst candidate for the ORR due to its high catalytic activity. As yet, there are still two major challenges for the Pt-based catalysts, one is high cost, and the other is insufficient electrochemical durability2-3. Therefore, the major effort in fuel cell research and development have been put on reducing Pt loading by exploring more effective synthesis technologies, and/or replacing Pt metal using other non-precious metals such as Fe, Co and Cu.
In this regard, carbon-based transition metal macrocycle complexes catalysts have become one of the most promising candidates to replace Pt/C catalyst, especially these catalysts synthesized after thermal treatment show high catalytic activity3,4. For revealing the mechanism of ORR and improving the ORR activity, one should know the active site in these catalysts. So far, there is a consensus that carbon, nitrogen and transition metals are all considered to be indispensable elements for the ORR activity5. However, for the transition metals, there is few report clearly point out whether it is a part of the active sites in these macrocycle complexes. In this work, with carbon-supported copper phthalocyanine tetrasulfonic acid tetrasodium salt, CuTSPc/C, as a target, the role of transition metal in macrocycle complexe was investigated by acid-leaching procedures.
The Electrochemical Conversion of Carbon Dioxide to Fuels on a Nanoporous Copper/M Catalyst
Authors: Billy Joshua , Co Anne C. 
Published: February 2020

Introduction

The electrochemical conversion of CO2 has been studied for many years, and copper is the only metal catalyst found to produce hydrocarbons1. This work examines the behavior of a nanoporous copper/M electrode when used as a catalyst for the electroreduction of CO2.

Materials and Methods

A copper/aluminum alloy was used as the starting material for producing a high surface area copper catalyst. The aluminum was removed through an etching procedure in strong base. The resulting nanoporous copper was crushed and mixed with Nafion, a binding agent, then casted over a copper foil substrate. After drying, transition metal (M) was galvanically displaced onto the copper to form nanoporous copper/M. Carbon dioxide electroreduction was performed by placing the catalyst in a specially designed flow cell. A bubbler in the cell was used to deliver CO2 to saturate the electrolyte, 0.1 M KHCO3, at a rate of 10 mL/min. The catalyst acts as the working electrode in this electrochemical cell. The product distribution from the electroreduction process was collected at a series of potentials. Gaseous products were identified and quantified using gas chromatography coupled with both mass spectrometry and a thermal conductivity detector. Liquid products were analyzed using nuclear magnetic resonance.
The surface morphology and composition of the catalyst was characterized using scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). The SEM images show a rough surface that retains a porous structure before and after experiments. Depth profiling studies with XPS show that the transition metal (M) from the surface of the material migrates to the bulk after electrolysis.

Results and Discussion

Identification of reduction products reveal that the catalyst is selective toward C2 species such as ethane and ethanol. This is a phenomenon that is also observed on nanoporous copper without the transition metal, while the addition of a transition metal changes the product selectivity. The only C1 species produced were carbon monoxide and formic acid, while no methane and methanol was detected. The most interesting product observed was n-propanol, a C3 species.
This work provides further insight into how selectivity of the CO2 reaction can be altered by tuning the catalyst properties. The use of a nanoporous copper catalyst provides an increased surface area and introduces many step edges, which are sites that are considered to be especially electrochemically active2. The role of the transition metal has yet to be determined, however future work will focus on optimizing the selectivity as a function of controlling the Cu/M (where M = transition metals) composition in the nanoporous copper framework.

References

1] Hori, Y.; Kikuchi, K.; Suzuki, S. Chem. Lett. 1985, 1695.
2] Billy, Coleman, Walz, Co, US 62/058,121.

Figure 1
High Activity of Ru@CoSe2/C Electrocatalyst Toward Oxygen Reduction Reaction
Authors: Li Hengyi , Cheng Xuan , Zhang Ying 
Published: February 2020

High electrocatalytic activity toward oxygen reduction reaction (ORR) of carbon supported Ru@CoSe2 catalysts (Ru@CoSe2/C) were prepared through a simple and facile two-step route. The CoSe2 nanoparticles were first obtained by microwave method, and then followed by galvanic substitution of Ru on CoSe2. The introduction of a small amount of Ru into CoSe2 led to a core-satellite structure in which the disordered Ru nanoparticles were adsorbed on the CoSe2 nanocrystallites. Compared with Ru85Se15/C[1] and CoSe2/C[2], the Ru@CoSe2/C exhibited higher ORR activity due to the enhanced Ru utilization through the interaction between Ru and CoSe2. Accordingly, the half-wave potential of 0.548 V and the cathodic current density of 3.37 mA cm-2 at 0.6 V were achieved for Ru@CoSe2/C in an acidic solution.
[1] Q. Zheng, X. Cheng, T. C. Jao, F. B. Weng, A. Su, Y. C. Chiang. Fuel cell performances at optimized Nafion and Ru85Se15 loadings in cathode catalyst layer.
Journal of Power Sources
201 (2012) 151-158
[2] H. Li, D. Gao, X. Cheng. Simple microwave preparation of high activity Se-rich CoSe2/C for oxygen reduction reaction.
Electrochimica Acta

138 (2014) 232-239
Synthesis and Electrochemical Properties of IrO2 Nanosheets
Authors: Shimizu Wataru , Ishida Takanobu , Miyasaka Syu , Ayato Yusuke , Sugimoto Wataru 
Published: February 2020

1. Introduction
IrO2 is known as one of the most highly active and stable OER catalysts. It is essential that high surface area materials are used, either by preparing porous architectures or dispersing nanoparticles on conducting supports since Ir is a precious metal. Two-dimensional nanosheets have recently attracted increased interest as building blocks for high surface area porous materials. Nanosheets with electronic conductivity, for example, RuO2 nanosheets find application in transparent conductive electrodes as well as electrochemical energy storage and conversion.1,2) IrO2 is analogous to RuO2in many aspects; both possess the rutile structure and are room-temperature metallic conductors. Here we report the successful synthesis of an ion exchangeable layered iridium oxide which can be exfoliated into elemental nanosheets and subsequently used as an electrocatalyst.
2. Experimental
Layered K0.30Ir0.93O2•nH2O was prepared by solid-state reaction of a 1:2 mixture of K2CO3 and IrO2 under inert atmosphere. Proton exchange was conducted by reaction in 1 M HCl for 3 days. Chemical exfoliation was conducted by shaking H0.30Ir0.93O2•nH2O in an aqueous solution of tetrabutylammonium hydroxide for 1 week. Electrochemical properties were studied in H2SO4 and HClO4.
Results and discussion
The Ir0.93O2 nanosheets (typical AFM image given in Fig. 1 inset) have an average thickness of c.a. 1.5 nm. The sharp edges suggest that the nanosheets are highly crystalline. Cyclic voltammograms of the Ir0.93O2 nanosheet electrode in 0.5 M H2SO4 is shown in Fig. 1. Three distinct redox peaks are observed. The E
1/2=0.95 and 1.19 peaks are typical of IrO2
3) and assigned to the Ir3+/Ir4+ and Ir4+/Ir5+ couple. The peaks at E
1/2=0.83 is observed only for IrO2 nanosheet, and shifts in HClO4; this peak is attributed to ad/desorption of anion. The onset of OER is observed at a potential similar to IrO2 nanoparticles.4) The specific capacitance between 0.2 and 1.2 V vs RHE at 2 mV s-1 was 93 kF mol-1, or 432 F g-1, which is the highest reported value for IrO2-based materials. It also closely matches the value of 88 kF mol-1 for RuO2nanosheet. Thus, almost all of the nanosheets surface is electrochemically accessible, and thus should provide unprecedented high utilization of the precious metal.
1) W. Sugimoto, H. Iwata, Y. Yasunaga, Y. Murakami, Y. Takasu, Angew. Chem. Int. Ed., 42, 4092 (2003).
2) K. Fukuda, T. Saida, J. Sato, M. Yonezawa, Y. Takasu, W. Sugimoto, Inorg. Chem., 49, 4391 (2010).
3) H. Andreas, H. Elzanowska, I. Serebrennikova, V.J. Birss. J. Electrochem. Soc., 147, 4598 (2000).
4) Y. Lee, J. Suntivich, K.J. May, E.E. Perry, Y. Shao-Horn, J. Phys. Chem. Lett. 3, 399 (2012).
Figure 1. Cyclic voltammograms of IrO2 nanosheet electrodes in 0.5 M H2SO4 at 50 mV -1 (inset shows a typical AFM image of nanosheets on Si).

Figure 1
Synthesis and Characterization of Cu, Fe, Co Based Non-Precious Metal Catalysts for ORR in Alkaline Fuel Cells
Authors: Goenaga Gabriel A. , Roy Asa Logan , Cantillo Nelly M. , Foister Shane , Zawodzinski Thomas A. 
Published: February 2020

The sluggish oxygen reduction reaction (ORR) in both proton exchange membrane and anion exchange membrane fuel cells, imposes the need for a catalyst to increase the reaction rate and overall cell efficiency. Pt, due to its high catalytic activity and relative stability, is currently the most used ORR catalyst. However, as a precious metal, Pt is expensive and a limited resource, greatly impacting the fuel cell’s cost and, as a consequence limiting its mass commercialization.
An advantage of alkaline fuel cells (AFCs) over proton exchange membrane fuel cells (PEMFCs) is that non-precious metals catalysts (NPMC) that are not very efficient for the ORR in acidic environment present higher catalytic activity and stability in alkaline media, even comparable to Pt. Synthesis of NPMCs is often inspired by natural systems. Enzymes, such as laccase, are very efficient ORR catalysts and are known to reduce oxygen at approximately 1.2 V vs. the reversible hydrogen electrode (RHE) under mild pH conditions.
We have synthesized a series of pyrolyzed NPMCs based on Cu, Co, Fe and their bimetallic combinations, and a phthalocyanine-like ligand supported on a carbon black. The as prepared catalysts are then pyrolyzed at temperatures ranging from 600 oC to 1000 oC. Various methods were used to optimize the catalysts activity; we evaluated the impact of different solvents during synthesis and removal of excess metal after pyrolysis. Catalyst ORR activity and stability in 0.1 M KOH were tested by rotating ring disk electrode (RRDE) experiment. Half wave potentials, number of electrons transferred and reaction rate were also calculated.
The bimetallic catalysts based on CoFe and CuFe surpassed the ORR activity of commercial Pt/C, reaching half wave potentials E1/2of 0.832 V and 0.815 V respectively, compared to 0.808 V vs. RHE of Pt/C. See figure 1.
The samples were characterized using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and x-ray powder diffraction (XRD). RRDE experiments were used to study the effect of catalyst loading, to determine the reaction order and catalyst stability. Ongoing experiments study the performance of the catalysts on a single cell using various anion exchange membranes.

Figure 1. RDE plots for Cu, Co, Fe based catalysts and their comparison to commercial 30% Pt/C.

Acknowledgments

We gratefully acknowledge the support of this work by the NSF-funded TN-SCORE program, NSF EPS-1004083, under Thrust 2.

References:

X. Li, B. N. Popov, T. Kawahara, H. Yanagi. J. Power Sources 196 (2011) 1717-1722.

H. Peng, F. Liu, X. Liu, S. Liao, C. You, X. Tian, H. Nan, F. Luo, H. Song, Z. Fu and P. Huang. ACS Catalysis 4 (2014) 3797−3805.

Figure 1
Inhibiting Effects of Nafion on ORR Catalyzed By Precious and Non-Precious Electrocatalysts Supported on Carbon
Authors: Chlistunoff Jerzy , Sansiñena José-María 
Published: February 2020

Nafion has been an ionomer of choice in polymer electrolyte fuel cells (PEFCs) for three decades.1 However, recent research studies demonstrate that the polymer has a number of undesired properties. One of such properties is its ability to restructure at the catalyst surface, which may lead to a partial blocking of the catalyst surface and thus an inhibition of the desired electrochemical reactions, i.e., oxygen reduction and hydrogen oxidation. While a simple evidence for the blocking was presented for ideal Pt/Nafion interfaces,2-5quantitative evaluation of such effects is much more difficult for highly dispersed catalysts, such as carbon supported Pt.
In this work, we will present results of our recent rotating ring disk electrode study on the inhibiting effects of Nafion on the electrocatalysis of oxygen reduction by carbon supported Pt and transition metal macrocycles. We will demonstrate that carbon plays an active role in the ORR inhibition and that the effects are especially strong for the non-precious catalysts (Fig. 1).

Acknowledgement

The financial support from the University of California (grant 12-LR-237440) is gratefully acknowledged.

References

1) G. H. McCain, M. J. Covitch, J. Electrochem. Soc., 131, 1350-1352 (1984).
2) J. Chlistunoff, F. Uribe, B. Pivovar, ECS Trans., 1,137-146 (2006).
3) J. Chlistunoff, F. Uribe, B. Pivovar, ECS Trans. 2, 37-46, (2006).
4) J. Chlistunoff, B. Pivovar, ECS Trans., 11, 1115-1125 (2007).
5) D. L. Wood, J. Chlistunoff, J. Majewski, R. L. Borup, J. Am. Chem. Soc., 131, 18096-18104 (2009).

Fig. 1. The effect of Nafion on ORR catalyzed by carbon (XC72) supported cobalt phthalocyanine (CoPC). Scan rate 10 mV s-1. Rotation rate 400 rpm. Catalyst ink composition: 46.5 mg XC72; 0.8 mg CoPC; 8 cm3 isopropanol; 41.9 μl 5% Nafion (solid line); 83.9 μl 5% Nafion (dotted line). Catalyst loading 0.1 mg (for XC72).

Figure 1
Platinum-Dysprosium Alloys for Oxygen Reduction in Alkaline Media
Authors: Sljukic Biljana , Santos Diogo M.F. , Martins Marta , Sequeira Cesar A.C. , Macciò Daniele , Saccone Adriana 
Published: February 2020

Oxygen reduction reaction (ORR) has become one of the most studied electrochemical reactions due to its fundamental complexity and great importance in practical applications [1]. Specifically, different renewable energy technologies, including metal-air batteries and fuel cells (FCs) [2], are based on this reaction. Direct borohydride fuel cells use alkaline sodium borohydride solution as fuel and oxygen as the oxidant.
The mechanism of the ORR is primarily determined by the electrode material and electrolyte solution. Recently, bimetallic alloys of Pt or Pd with rare earth (RE) metals scandium (Sc) or yttrium (Y) were suggested as novel electrocatalysts for the ORR based on density functional theory calculations [3]. Electrochemical measurements have confirmed improved activity of polycrystalline Pt3Sc and Pt3Y electrodes in comparison with pure Pt by a factor of 1.5 - 1.8 and 6 - 10, respectively, in the range 0.9 - 0.87 V.
Herein, platinum-dysprosium (Pt-Dy) alloys, with different amounts of RE metal (50 to 60 at.%) were prepared by arc-melting starting from the stoichiometric amounts of the two metals and their composition and structure were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy.
Subsequently, electrocatalytic activity for the ORR of Pt-Dy alloy electrodes was studied in alkaline solution by cyclic voltammetry (CV) and chronoamperometry (CA). Main kinetic parameters, namely charge transfer coefficient and number of electrons exchanged, were evaluated for temperatures ranging from 25 to 65 ºC.
Furthermore, electrocatalytic activity for the ORR was studied in the presence of sodium borohydride in the supporting electrolyte in order to simulate conditions in direct borohydride fuel cells where borohydride crossover is possible to occur.
References
[1] Lee, J.; Jeong, B.; Ocon, J. D. Oxygen Elecrocatalysis in Chemical Energy Conversion and Storage Technologies. Current Applied Physics
2013, 13, 309.
[2] Mulder, G. Fuel Cells – Alkaline Fuel Cells | Overview. Encyclopedia of Electrochemical Power Sources
2009, 321.
[3] Greeley, J.; Stephens, I. E. L.; Bondarenko, A. S.; Johansson, T. P.; Hansen, H. A.; Jaramillo, T. F.; Rossmeisl, J.; Chorkendorff, I.; Nørskov, J. K. Alloys of Platinum and Early Transition Metals as Oxygen Reduction Electrocatalysts. Nature Chemistry
2009, 1, 552.
(Invited) Oxygen Reduction Reaction at Cathodes on Proton Conducting Oxide Electrolytes: Contribution from Three Phase Boundary Compared to Bulk Path
Authors: Merkle Rotraut , Poetzsch Daniel , Maier Joachim 
Published: February 2020

So far, the oxygen reduction reaction for cathodes on proton conducting electrolytes such as acceptor-doped BaZrO3 is less well understood than for cathodes on oxide ion conductors. Two groups of reaction pathways can be hypothesized: (i) without involvement of oxygen vacancies (which are, in contrast to cathodes on oxide conducting electrolytes, not required for the overall reaction on proton conducting electrolytes), (ii) with involvement of oxygen vacancies as catalytically active center, where the vacancies are restored at the end of the reaction by water desorption. Reaction rates for different steps being rate determining are derived, considering also the dependence of point defect concentrations on both pO2 and pH2O. These predictions are compared to experimental findings.
By thermogravimetry, a proton concentration in the range of 0.1-1mol% could be detected in Ba0.5Sr0.5Fe0.8Zn0.2O3-
d (BSFZ) under humid conditions.[1] Impedance measurements on pore-free BSFZ and Ba0.5Sr0.5Co0.8Fe0.2O3-
d (BSCF) microelectrodes show that their proton conductivity suffices for the oxygen reduction reaction to proceed by the "bulk path" on the whole surface area.[2] In the analysis of these measurements on gas-symmetrical cells, the influence of the perceptible hole conductivity of the BaZr1-xYxO3-x/2 proton conducting electrolyte in high pO2must properly be accounted for.[3]
The measured pO2 and pH2O dependencies indicate that molecular oxygen species and oxygen vacancies are involved in the rate determining step. Thus, it appears that at least for perovskites such as BSFZ and BSCF with high oxygen vacancy concentration, the early steps of oxygen reduction are similar for cathodes on oxide conducting and proton conducting electrolytes, and differ only in the later stages (oxygen incorporation and transfer to the electrolyte vs. water desorption).
[1] D. Poetzsch, R. Merkle, J. Maier, Phys. Chem. Chem. Phys. 16 (2014) 16446
[2] D. Poetzsch, R. Merkle, J. Maier, in preparation
[3] D. Poetzsch, R. Merkle, J. Maier, J. Power Src. 242 (2013) 784