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When hydrogen is produced by electrolysis the possibility of water stress in some populations and scarcity of precious metals for catalyst production are seen as future barriers. The use of non-precious metal catalysts allied to direct saltwater splitting reduce the pressure on scarce resources. Here, four Metal-Nitrogen-Carbon (M-N-C) catalysts were synthesized with metal salts of Co, Fe, Ni and FeNi, with 1,5-diaminonhaptalene as N-C source. These catalysts were compared with a blank N-C without metal and a Pt/C commercial catalyst. Tests were conducted in electrolyte solution 0.5 M of H2SO4 and 0.5 M of NaCl. Results showed limited activity towards Hydrogen Evolution Reaction (HER) compared with Pt/C and other non precious metal catalysts. Nevertheless, points out trends for better catalyst synthesis as improved activity of FeNi catalyst in acidic media and saltwater.

A variety of techniques for management of carbon dioxide emissions from power generation facilities and other industrial sites have been under active investigation for decades, in an effort to mitigate the environmental impacts of these releases. Once such approach is electrochemical reduction, which treats the waste CO2 as a source material for the production of value-added materials. Currently, the most promising form factor for this electrocatalytic application appears to be a stack-based system, where catalyst is immobilized on porous media that is interfaced with a liquid or solid electrolyte, and the reactant carbon dioxide is delivered to the active region by gaseous diffusion, which is orders of magnitude faster that diffusion though aqueous media. Various carbonaceous reduction products can be created depending on the composition, size, and microstructure of the catalyst particles, including formic acid/formate, carbon monoxide, alcohols, and hydrocarbons. In general, smaller catalyst particles, ideally in the nanoparticulate (<< 1 μm) range, tend to yield superior catalytic performance, due to a combination of factors such as a higher density of exposed grain boundaries and a higher fraction of exposed crystalline facets that are uncommon in particles of micron size or larger.This talk will survey recent work illustrating the ability of pulse/pulse-reverse electrodeposition processes to tune the size of particles applied to gas-diffusion electrode substrates, with a primary focus on two single-metal catalyst materials relevant to carbon dioxide electroreduction: tin and copper. The former is a catalyst primarily for formic acid production, while the latter is unique among single-metal catalysts as the only element known to date to produce significant amounts of hydrocarbons and/or alcohols. Particle morphology and representative particle size will be discussed as a function of pulsed electrodeposition waveform parameters, with the goal of highlighting overarching trends across the waveform space.

Space programs around the globe have begun to consider the logistical demands of missions beyond the orbital neighborhood of Earth. Unlike local installations such as the International Space Station, long-range missions will not have the option to resupply critical materials from Earth. Thus, the development of capabilities for what is often termed “In-Situ Resource Utilization” (ISRU) have been a continuing focus of research through NASA and other agencies. One particular long-range mission of interest is to place human astronauts on Mars; the major component of the thin Martian atmosphere is carbon dioxide, making CO2 a natural input to ISRU technologies for production of carbon-containing materials. Production of mission consumables from in-situ Mars resources will be critical to enabling human exploration of Mars, in part by minimizing the number and size of descent/ascent vehicles. Potential ISRU products from CO2 include that seem likely to provide significant mission benefits with minimal infrastructure required are propellants (e.g., hydrocarbons), fuel cell reactants (e.g., formic acid, methanol, carbon monoxide), and life support consumables (e.g., oxygen). The first portion of this talk will comprise a high-level overview of the chemical transformations that can be imparted to CO2 via electrocatalysis on gas-diffusion electrodes (GDEs), in the form of a summary of literature reports on the catalytic performance of a wide variety of single-metallic and metal-alloy systems. The remainder will encompass an exposition of the electrocatalytic performance of tin and copper single-metal GDE electrocatalysts prepared by pulsed electrodeposition. These metals are well known for their ability to reduce carbon dioxide to formic acid and hydrocarbons/carbon monoxide, respectively, and are under active development in numerous academic research groups and industrial entities to this end. These experimental results clearly demonstrate the power and flexibility of the pulse/pulse-reverse electrodeposition approach to catalyst fabrication, as evidenced by the appreciable effects of the pulsed-waveform electrodeposition parameters on CO2 electroreduction product distribution and total current density.

It is well accepted that adsorbed CO (COad) on Pt electrode reacts with water (or oxygenated species). We have recently found that COad also reacts with methanol and ethanol to form methyl formate (COad + CH3OH → HCOOCH3) and ethyl formate (COad + C2H5OH → HCOOC2H5), respectively, by using surface-enhanced infrared absorption spectroscopy and high-performance liquid chromatography. In the present report, we estimate the rate constants of the reactions by considering that the reactions proceed via Langmuir-Hinshelwood mechanism. The rate constants are estimated to be in the order of 0.1 s-1.

In this work, we demonstrate layered manganese oxide with potassium intercalated cation (K-birnessite) as a bifunctional electrocatalyst for Zn-air battery with an open circuit potential (OCP) of 1.31 V versus Zn/Zn2+. Zn-air battery using K-birnessite catalyst exhibits a small potential gap between discharge and charge potential of 0.79 V measured via galvanostatic discharge-charge technique at a current density of 2 mA cm-2 in the ambient air with 2 hr per cycle. Moreover, the cyclability of Zn-air battery using K-birnessite measured with a short period of 10 min per cycle exhibits cyclable stability over 10 hr which is better than the Zn-air battery using the state-of-art mixed catalyst of Pt/C and RuO2 (8 hr). This 2D layered K-MnO2 may be practically used as a bifunctional catalyst in metal-air batteries.

Nickel and nickel-based nanomaterials are an attractive choice to replace noble metals as electrocatalyst in alkaline direct alcohol fuel cells (DAFCs) owing to their lower cost and suitable electrocatalytic activity. Among the different synthetic methods available for the production of nanostructured materials, galvanostatic electrodeposition offers a fast and simple means of fabricating active electrodes. Therefore, thin-layers of nickel were electrodeposited onto polycrystalline gold electrodes using constant current pulses from an electrolyte containing 50 mM NiSO4. The electrocatalytic properties of the nickel nanostructures in alkaline medium, in which the catalytic species NiOOH is formed, were evaluated through cyclic voltammetry in 0.5 M methanol + 1 M KOH. The effects of current density pulse and the presence of sulfate or chloride anions in the supporting electrolyte on the electrocatalytic activity of the deposits were studied using Ni(OH)2 surface concentration, Gamma, and electrocatalytic intensity, EI, as performance parameters. It was found that highest electrolcatalytic activities were obtained when using current densities pulses close to 4.0 mA/cm2 in the presence of sulfates. It was found that the presence of sulfates leads to a strong correlation between the electrocatalytic activity for the oxidation of methanol and the surface concentration of Ni(OH)2.

Precise characterization of activities is crucial for benchmarking and mechanistic examinations of electrocatalysts. In this study, the importance of surface areas to correctly characterize the activities of electrocatalysts is discussed. Exemplified for the hydrogen evolution reaction (HER) on a smooth and porous gold electrode, normalization of the activity to the geometric surface areas of the electrodes lead to activities that deviate by orders of magnitudes. Normalization to the electrochemically active surface areas (ECSAs) as determined by capacitance measurements lead to similar activities. To verify if surface areas of different electrodes can be correctly estimated by capacitance measurements, we examined a choice of noble (Au, Pt, Rh, Ir) and non-noble (Ni, Co, Ti, Nb) metal electrodes. The capacitances of all examined metals are individually affected by potential and passivation layers or specific adsorption processes of ions and/or molecules. Thus, the measured capacitances often deviate from the double layer capacitance that is typically used to estimate the ECSA. Accordingly, capacitance measurements to estimate the ECSA must be carefully evaluated and can only be correctly applied in certain frameworks.

In this contribution, we demonstrate the presence of high-spin Fe3+ in Fe-substituted ZrO2 (FexZr1−xO2−δ), as deduced from X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and 57Fe Mössbauer spectroscopy measurements. The activity of this carbon-supported FexZr1−xO2−δ catalyst towards the oxygen reduction reaction (ORR) was examined by both the rotating (ring) disk electrode (R(R)DE) method and in single-cell proton exchange membrane fuel cells (PEMFCs). DFT calculations suggest that the much higher ORR mass activity of FexZr1−xO2−δ compared to Fe-free ZrO2 is due to the enhanced formation of oxygen vacancies: their formation is favored after Zr4+ substitution with Fe3+ and the oxygen vacancies create potential adsorption sites, which act as active centers for the ORR. H2O and/or H2O2 production observed in RRDE measurements for the Fe0.07Zr0.93O1.97 is also in agreement with the most likely reaction paths from DFT calculations. In addition, Tafel and Arrhenius analyses are performed on Fe0.07Zr0.93O1.97 using both RRDE and PEMFC data at various temperatures.

The performance of electrocatalysts for the electrochemical carbon dioxide (CO2) reduction reaction (eCO2RR) is largely dependent on the ability to efficiently deliver CO2 to the active sites. A variety of reactor configurations have been explored in the literature that can be broadly classified as based on either liquid- or gas-phase reactant delivery. These configurations utilize a range of electrode types including metal plates, meshes, packed granules, and gas diffusion electrodes (GDEs) [1]. Amongst these methods, the use of gas-phase reactor designs employing GDEs enables a dramatic increase in current density (typically an order of magnitude or larger) over liquid-phase reactor designs, where the low solubility and aqueous diffusivity of CO2 result in severe mass transport limitations.However, the performance of GDEs in various CO2 electroreduction processes can be hampered by poor catalyst utilization and transport limitations within the catalyst layer. At higher catalyst loadings (thicker catalyst layers), which are desirable for high production rates, conversion efficiencies drop and undesirable side product formation (both from hydrogen evolution and diversion of carbon to alternative reaction pathways) increases due to reactant starvation. Reducing particle size typically enhances both catalyst utilization and activity per unit mass. This, in turn, may enable thinner catalyst layers, mitigating or avoiding such decreases in product selectivity. While synthesis methods exist for generating smaller (< 10 nm) particles, these particles must still be deposited on a gas-diffusion layer (GDL) substrate such that ionic and electronic contact can be maintained with the electrolyte and GDL, respectively.Previous work directed towards platinum (Pt) catalyst utilization in polymer electrolyte fuel cell GDEs demonstrated an “electrocatalyzation” (EC) approach that used pulse and pulse-reverse electrodeposition to obtain highly dispersed and uniform Pt catalyst nanoparticles (~5 nm) [2-4]. Moreover, since the catalyst was electroplated through an ionomer layer onto the bare GDL, the formed nanoparticles were inherently in both electronic and ionic contact within the GDE and, consequently, utilization was enhanced. Specifically, for the oxygen reduction reaction, the electrodeposited catalyst exhibited equivalent performance at 0.05 mg/cm2 loading compared to a conventionally prepared GDE with a loading of 0.5 mg/cm2 [4].This talk will discuss the electrodeposition of tin (Sn) and copper (Cu) onto both commercially-available and custom-fabricated GDLs through an EC process, and the electrocatalysis performance of these catalysts as compared to state-of-the-art Sn and Cu nanoparticle catalysts (75-150 nm) prepared by spray-coating. Testing in a custom flow-cell electroreactor has demonstrated that the EC GDEs exhibit electrocatalytic performance comparable or superior to both literature reports and the spray-painted catalysts. Further, clear effects of the pulsed-waveform EC parameters on product distribution and total current density will be highlighted. Preliminary work toward development of GDLs robust against electrolyte saturation/penetration over many hours of operation will also be discussed. In summary, the highly scalable EC approach appears promising for fabricating active catalytic layers directly onto GDL substrates for carbon dioxide reduction applications.References[1] I. Merino-Garcia, E. Alvarez-Guerra, J. Albo, A. Irabien, Chemical Engineering Journal, 305 (2016) 104-120.[2] M. E. Inman, E.J. Taylor, in, U.S. Patent No. 6,080,504, 2000.[3] N .R.K. Vilambi Reddy, E. B. Anderson, E.J. Taylor, in, U.S. Patent No. 5,084,144, 1992.[4] E.J. Taylor, E.B. Anderson, N.R.K. Vilambi, Journal of The Electrochemical Society, 139 (1992) L45-L46.