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Exploiting renewable energy sources to drive CO2 reduction electrochemically into value-added products has gained tremendous attention towards reducing the greenhouse effect. Upstream processes for capturing and purifying the CO2 raise the overall cost of the electrolysis system. Direct reduction of flue gas into value-added C2+ products has attained much consideration in recent years. However, the sensitivity of the cathode catalyst performance in the presence of flue gas contaminants, particularly O2, and strong competition from the hydrogen evolution reaction in aqueous electrolyte are major challenges for such an approach. Herein, the influence of flue gas contaminants on electrochemical reduction of CO2 in acidic nonaqueous methanol to a methyl formate product has been investigated on a Pb-catalyzed electrode in conjunction with aqueous anolyte for the promotion of a sustainable water oxidation half-reaction. The presence of 4% O2, 0.05% SO2, and 0.05% NO is shown to have minimal effect on the total faradaic efficiency of CO2 reduction products. CO2 concentration-dependent measurements reveal declining CO2 reduction faradaic efficiencies corresponding to the decrease in partial pressure, which is attributed to CO2 mass transfer limitations to the electrode surface. XPS analysis displays the relative stability of the Pb working electrode before and after the electrochemical operation during exposure to flue gas components, which further highlights the promising tolerance of this system for direct flue gas conversion. Figure 1

The conversion of waste CO2 to value-added chemicals through electrochemical reduction is a promising technology for mitigating climate change while simultaneously providing economic opportunities. The use of the nonaqueous solvent methanol allows for higher CO2 solubility and novel products through the incorporation of methanol as an intermediate. In this work, the electrochemistry of CO2 reduction in acidic methanol catholyte at a Pb working electrode was investigated while using a separate aqueous anolyte to promote a sustainable water oxidation half-reaction. The selectivity among methyl formate (a product unique to reduction of CO2 in methanol), formic acid, and formate was critically dependent on the catholyte pH, with a faradaic efficiency for methyl formate as high as 75% measured in pH < 2. Furthermore, strategies to limit the concentration of formic acid and maintain the surface oxide of the catalyst have been shown to be effective at improving the steady-state durability of the CO2-to-methyl formate process. Tests with simulated flue gas as the feedstock have shown a high level of tolerance for the Pb-catalyzed electrolysis to SO2, NO, and dilute O2 contaminants. Finally, a comparative technoeconomic analysis will be discussed to highlight target performance metrics and the viability of alternate pathways for electrochemical conversion of CO2 to methyl formate.

The conversion of waste CO2 to value-added chemicals through electrochemical reduction is a promising technology for mitigating climate change while simultaneously providing economic opportunities. The use of the nonaqueous solvent methanol allows for higher CO2 solubility and novel products through the incorporation of methanol as an intermediate. In this work, the electrochemistry of CO2 reduction in acidic methanol catholyte at a Pb working electrode was investigated while using a separate aqueous anolyte to promote a sustainable water oxidation half-reaction. The selectivity among methyl formate (a product unique to reduction of CO2 in methanol), formic acid, and formate was critically dependent on the catholyte pH, with a faradaic efficiency for methyl formate as high as 75% measured in pH < 2. Tests with simulated flue gas as the feedstock have shown a high level of tolerance for the Pb-catalyzed electrolysis to SO2, NO, and dilute O2 contaminants.

Plasmas have a number of unique properties which researchers may be able to leverage to enhance desired electrocatalyst material properties and steer electrochemical reaction performance. Two examples of the recent application of plasmas for advancements in electrochemical fuel production are presented. In the first, the nonequilibrium reaction environment of an air plasma enabled the synthesis of homogeneous phases of metastable compositions of a mixed W1-xIrxO3-δ alloy. For a low-platinum-group-metal (PGM) composition of only 1% Ir, plasma-synthesized W0.99Ir0.01O3-δ was observed to be an acid-stable oxygen evolution reaction (OER) catalyst of competitive overpotential. Moreover, the plasma-synthesized alloy was observed to have an OER overpotential ~ 570 mV less than that of a thermally oxidized alloy of the same composition. In the second example of a plasma enhancement, a nitrogen plasma was coupled into the cathode of a proton exchange membrane electrolyzer to provide energetically activated N2 species to the electrocatalyst surface and demonstrate a proof-of-concept synergistic enhancement in the rate of ammonia production. At an applied bias of ~3.5 V across the electrolyzer, plasma-assisted operation was observed to produce 47% more ammonia than the combination of plasma-without-bias and bias-without-plasma conditions.

Semiconductors of the III-V class are among the most promising materials for high efficiency solar fuels applications, particularly in tandem devices. Unfortunately, these materials are known to undergo oxidative corrosion as photoanodes in strongly acidic or alkaline electrolyte. In striving to overcome this challenge, researchers need to understand the fundamental degradation behavior during photoelectrochemical operation. Studying the in-situ photocorrosion process has largely been limited thus far to expensive and labor-intensive techniques that are not widely available in most labs. Herein, the corrosion of n-GaP, a promising III-V material for tandem top subcells, was investigated in strongly acidic electrolyte using an in-situ UV-Vis spectroscopy technique to monitor dissolved Ga and P species as a function of applied bias and time. The changing faradaic efficiency of the electrochemical GaP oxidation reaction was calculated from this data and used to interpret the corrosion process in conjunction with SEM and XPS characterization. Most notably, p+-GaP and n-GaP displayed strikingly different corrosion behavior, with p+-GaP dissolving uniformly across the active area and the corrosion faradaic efficiency increasing to a steady value. Illuminated n-GaP, in contrast, showed initially high corrosion faradaic efficiency which decreased during operation and was attributed to the phenomena of anisotropic surface etching and micropore formation during the beginning stages of photoanodic operation. In addition, corrosion measurements were made with thin conformal coatings of TiO2 as a protective barrier layer on the GaP surface. Although the protective coating slowed the rate of GaP dissolution, the TiO2 layers produced herein contributed significant charge-transfer resistance and still showed similar trends in the corrosion faradaic efficiency vs. time as the bare n-GaP.

Plasmas have a number of unique properties which researchers may be able to leverage to enhance desired electrocatalyst material properties and steer electrochemical reaction performance. Two examples of the recent application of plasmas for advancements in electrochemical fuel production are presented. In the first, the nonequilibrium reaction environment of an air plasma enabled the synthesis of homogeneous phases of metastable compositions of a mixed W1-xIrxO3-δ alloy. For a low-platinum-group-metal (PGM) composition of only 1% Ir, plasma-synthesized W0.99Ir0.01O3-δ was observed to be an acid-stable oxygen evolution reaction (OER) catalyst of competitive overpotential. Moreover, the plasma-synthesized alloy was observed to have an OER overpotential ~ 570 mV less than that of a thermally oxidized alloy of the same composition. In the second example of a plasma enhancement, a nitrogen plasma was coupled into the cathode of a proton exchange membrane electrolyzer to provide energetically activated N2 species to the electrocatalyst surface and demonstrate a proof-of-concept synergistic enhancement in the rate of ammonia production. At an applied bias of ~3.5 V across the electrolyzer, plasma-assisted operation was observed to produce 47% more ammonia than the combination of plasma-without-bias and bias-without-plasma conditions.

The electrolytic conversion of CO2 to useful fuels and chemicals is a promising technology for greenhouse gas reduction and waste utilization, but converting CO2 to larger multicarbon products with any selectivity is a major challenge. However, commercial electrolyzers for the conversion of CO2 to CO at high current density and high yield are in development. Subsequent electrochemical reduction of carbon monoxide affords the possibility of promoting a different reaction pathway for higher multicarbon product selectivity. The reaction conditions for the aqueous conversion of CO on Cu/CuOx catalyst have been explored including applied bias, gas flow rate, and oxide thickness. Significant faradaic efficiencies for C4 products (> 5% FE), including gamma-hydroxybutryic acid and succinic acid, were observed and quantified via NMR. The gas flow rate and resulting hydrodynamics of CO near the catalyst surface play a crucial role, with little C4 species observed at lower flow rates. A proposed reaction pathway for the formation of these C4 products will be presented as well.

One outstanding research challenge in water-splitting electrocatalysis is that few known materials have both high catalytic activity and extended stability for the oxygen evolution reaction in acidic electrolytes, and these have primarily been limited to noble metal oxides. A rapid and scalable novel plasma synthesis technique has been employed to fabricate mixed metal oxide compositions of homogeneously phase-pure catalysts with an aim toward the development of acid-stable OER catalysts of low noble metal content. In particular, a composition of W0.9Ir0.1Ox has been characterized and shows high activity and stability at pH 0 following a standardized benchmarking protocol. A high-throughput plasma reactor nanoparticle printer has been developed to enable the rapid search for acid-stable OER catalysts with minimal to no platinum-group-metal elements. Such materials could improve the sustainability and economic competitiveness of proton exchange membrane electrolyzers.

Photoelectrochemical water splitting cells comprising the alloys of III-V semiconductors hold record solar-to-hydrogen efficiencies. However, the performance of state-of-the art III-V alloy-based single absorber devices, particularly of InGaP2, InGaAs, GaPN, and GaAsN, comes short of unassisted water due to a) inadequate alignment of band edges with respect to the HER and OER redox potentials, b) insufficient photovoltage to favor charge separation at the solid electrolyte liquid junction, and/or iii) recombination. In order to circumvent these limitations considerable research efforts have been directed at creating more complex architectures involving e.g. tandem cells, nanostructures, and buried junctions to correctly position the bands and provide enough driving force to surmount overpotentials and the 1.23 eV energetic barrier of the water splitting reactions. Therefore, developing novel III-V photoabsorbers with adequate band energetics is key to conceiving simpler, yet efficient single semiconductor PEC cells for production of solar fuels at a competitive cost. First-principles DFT+U calculations incorporating the local density approximation and generalized gradient approximation have shown that incorporation of Sb narrows the band gap in Ga(Sbx)N1-x and changes the electronic band gap from indirect to direct in GaSbP. Theoretical computations predict that, with band gaps in the order of 2 eV, these materials straddle the potential window for water oxidation and proton reduction in acidic solution. Single crystalline films of these two materials have been deposited by metal organic chemical vapor deposition and halide vapor phase epitaxy, in a wide range of Sb incorporation without phase segregation. Experimental results corroborate the significant band gap reduction in GaSbN from 3.4 to 1.5 eV(Fig 1a) and suggest the reduction of the indirect band gap of GaP when Sb is incorporated(Fig 1b) as determined by Tauc plot analysis of diffuse reflectance data, low temperature photoluminescence spectroscopy, and photocurrent spectroscopy. Electrodes comprising Ga(Sbx)N1-x and Ga(Sbx)P1-x have been benchmarked employing 2- and 3-electrode standard methods for assessment of their characteristic attributes, i.e. flat-band and onset potentials, photovoltage, zero-bias photocurrent density, fill factors, carrier concentrations, and most importantly, their ability for gas evolution by in situ fluorescence probing. New insights into these materials regarding the donor concentration in GaP alloys, and the effect of incorporation help in fundamentally understanding the thermodynamics at a solid liquid electrolyte interface and work function of GaSbP to realize the full potential of these novel III-V alloys. This poster will highlight recent advances in the understanding of the inter-relationship of processing/synthesis, material structure and photoelectrochemical properties of this new class of materials. Acknowledgements: Financial support from US Department of Energy (DE-FG02-07ER46375) and NSF (DMS1125909). References: 1. R.M. Sheetz, E. Richter, A.N. Andriotis, C. Pendyala, M.K. Sunkara and M. Menon, “Visible light absorption and large band gap bowing in dilute alloys of gallium nitride with antimony”, Phys. Rev. B, 84, 075304 (2011) 2. S. Sunkara, V.K. Vendra, J.B. Jasinski, T. Deutsch, A.N. Andriotis, K. Rajan, M. Menon and M.K. Sunkara, "New Visible Light Absorbing Materials for Solar Fuels, Ga(Sbx)N1-x”, Adv. Mater., 26 (18), 2878-2882 (2014) 3. S. Sunkara et al., “Band Gap Engineering of Gallium Antimony Nitride Alloy Nanowires and Photoelectrochemical Properties”, To be submitted (2016). 4. H. Russell et al., “Direct Band Gap Gallium Antimony Phosphide GaSbxP1-x Alloys”, Scientific Reports 6, (2016).

Paramount to the global action plan on climate change is the renewable energy technology that drives carbon neutrality goal, and vital in this pursuit is the addressing of material challenges currently facing this technology. To properly address this issue, a synthesis technique capable of accelerating the discovery of materials for various energy conversion and storage applications needs to be developed. Here we present a technique that allows rapid and controlled synthesis of mixed metal oxide particles using plasma oxidation of liquid droplets containing mixed metal precursors1. The conventional wet chemical methods for synthesis of multimetal oxide solid solutions often require time-consuming high pressure and temperature processes, and so the challenge is to develop rapid and scalable techniques with precise compositional control. The concept is demonstrated by synthesizing binary and ternary transition metal oxide solid solutions with control over entire composition range using metal precursor solution droplets oxidized using atmospheric oxygen plasma. The results show the selective formation of metastable spinel and the rocksalt solid solution phases with compositions over the entire range by tuning the metal precursor composition. The synthesized manganese doped nickel ferrite nanoparticles, NiMnzFe2−zO4 (0 ≤ z ≤ 1), exhibits considerable electrocatalytic activity toward oxygen evolution reaction, achieving an overpotential of 0.39 V at a benchmarking current density of 10 mA/cm2 for a low manganese content of z = 0.20. References 1. Ajayi, B. P., S. Kumari, et al. (2016). "A rapid and scalable method for making mixed metal oxide alloys for enabling accelerated materials discovery." Journal of Materials Research, 1-12 doi: http://dx.doi.org/10.1557/jmr.2016.92

The electrochemical carbon dioxide reduction mechanism is a complex reaction pathway dependent on the active catalyst surface and intermediate species binding energy, convoluted with the competing effects of kinetics and mass transport. The nature of the photoelectrochemical semiconductor/catalyst interface and the optical interactions occurring there provide a unique opportunity to possibly affect the carbon dioxide reduction mechanism and influence the reaction pathway. For CO2 reduction under continuous 1-Sun illumination, Cu-catalyzed p-Si photocathodes demonstrated the same general product faradaic efficiency trends as dark Cu electrocatalysts, but offset by the photovoltage of the photocathode. Under chopped illumination, however, the product distribution at a given potential changed significantly and depended on the chopping frequency. The results are discussed along with the proposed effects of the chopped illumination on mass transfer and on the electrode interface which lead to the observed mechanistic shifts.

Many grand challenges in energy conversion and storage need discovery of new materials. However, there are not too many reported synthesis approaches that could easily be implemented for screening and rational understanding of structure-behavior relationships. Specifically, the challenges include semiconductors for photoelectrochemical water splitting, stable electrocatalysts for oxygen evolution and reduction, and nitrogen reduction and for many heterogeneous gas-solid reactions including carbon dioxide reduction. Many of the above challenges require synthesis of multi-element alloys with composition over entire range regardless of phases present. Here, we report a new synthesis technique that can be used to accelerate the discovery of materials for various energy conversion and storage applications. Specifically, this technique allows a rapid and controlled synthesis of mixed metal oxide particles using plasma oxidation of liquid droplets containing mixed metal precursors. The conventional wet chemical methods for synthesis of multi-metal oxide alloys often require time-consuming high pressure and temperature processes, and so the challenge is to develop rapid and scalable techniques with precise compositional control. The concept is demonstrated by synthesizing binary and ternary transition metal oxide alloys with control over entire composition range using metal precursor solution droplets oxidized using atmospheric oxygen plasma. The results show the selective formation of metastable spinel and the rocksalt solid solution phases with compositions over the entire range by tuning the metal precursor composition. The synthesized manganese doped nickel ferrite nanoparticles, NiMnzFe2- zO4 (01), exhibits considerable electrocatalytic activity towards oxygen evolution reaction (OER), achieving an overpotential of 0.39V at a benchmarking current density of 10 mAcm-2 for a low manganese content of z = 0.20.

Copper is one of the most commonly studied materials for the electrochemical conversion of carbon dioxide (CO2) into valuable chemical products. Numerous efforts have been made to enhance the product selectivity - an important characteristic essential for efficient chemical production from CO2 - of Cu with only marginal progress. Here, we introduce a pulsed-bias technique for the electrochemical reduction of CO2 on Cu catalyst which led to 100% selectivity for CO formation over other carbon products and only produced syngas (CO + H2). X-ray photoelectron spectroscopy (XPS) and controlled CO2 electrochemical reduction experiments suggest that in-situ oxidation and reduction of the Cu causes the preference for CO formation over other carbon products on polycrystalline Cu. Moreover, the observed pulse waveform dependency of the H2 to CO product ratio can also be beneficial by allowing tunable CO2 reduction products as a controllable syngas feedstock for different industrial applications (e.g., Fischer-Tropsch process, and hydroformylation of alkenes to aldehydes) without an additional hydrogen source. This study opens a new route for the selective conversion of CO2 into syngas on robust and cost-effective Cu catalysts, which could be adopted at large scale in the chemical industry. Keywords: Copper, Catalyst, CO2reduction, Syngas, Selectivity, Electrochemistry

Solar photovoltaic utilities require large land areas to produce power equivalent to a conventional fossil fuel utility, and also must be coupled to cost-effective energy storage to overcome the intermittency of sunlight and provide reliable, continuous energy generation. To target both of these disadvantages, a method was demonstrated to produce hydrogen fuel from solar energy by splitting seawater vapor from ambient humidity at near-surface ocean conditions. Using a proton exchange membrane electrolyzer with seawater-humidified air at 80% relative humidity at the anode and dry N2 at the cathode, sufficient electrolysis current density was maintained to operate near the maximum energy-conversion point when driven by a triple-junction amorphous Si solar cell of equivalent area. Fluctuations in atmospheric water content were demonstrated to have minimal effect on the solar-to-hydrogen efficiency, remaining ~ 6% with relative humidity ≥ 30%. Direct solar-driven H2 production from seawater vapor was maintained at > 4.5 mA cm-2 for > 90 hours. The calculated solar-to-hydrogen conversion efficiency before and after 50 h of operation changed from 6.0% to 6.3% using an ambient seawater humidity feedstock as compared to a drop from 6.6% to 0.5% using liquid seawater feedstock.

Organic-inorganic halide perovskites have created a breakthrough in the field of solar cells because of their low cost, low temperature processibility and excellent optoelectronic properties. However, the instability of organic-inorganic halide perovskites to moisture is currently a huge challenge in the field of perovskite solar cells and needs to be addressed to translate the perovskite technology from the laboratory bench to large scale industrial practice. Currently, all the lab scale perovskite cells are fabricated in controlled glove box atmosphere with less than 1 % relative humidity to prevent their deterioration under moisture. In this work, a novel concept of protecting the perovskite using a highly conductive composite of a layered material and a hole transporting polymer is presented. The excellent charge transport properties of the composite coating allow the use of thick coating on the perovskite, creating extremely high length scales for moisture diffusion through composite. The composite coating developed in our work, could be extended to lead-free organometallic perovskites that are both moisture and oxygen sensitive. The deposition of gold as a counter electrode for the lab scale perovskite cells is usually performed by thermal evaporation in a bell jar evaporator. This process is time consuming, energy intensive and not viable to scale up. Our approach involving lamination of individual electrodes, enables a much facile low cost process for fabricating perovskite solar cells. Our results and observation on polymer composites as protective coatings for perovskite and on laminating electrodes show high promise for the scalability and low cost fabrication of perovskite cells under atmospheric conditions (60 -70 % relative humidity). In addition, the degradation mechanisms involving both moisture and oxygen in the presence of UV light irradiation will be discussed.

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