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Green ammonia production is facing increasing interest on a global scale as a hydrogen carrier for power generation as well as fertilizer for food production. The conventional Haber-Bosch method for ammonia synthesis is energy demanding, requires high purity hydrogen, and is based on fossil fuels. A preliminary techno-economic model for electrochemical ammonia synthesis at near ambient pressure using feed rates of 32 metric ton/day for hydrogen and 135 metric ton/day for nitrogen is presented in this study. Various pathways using different methods for nitrogen generation and hydrogen production were investigated to gain insight into added energy savings per metric ton of ammonia. Electrochemical synthesis using electrolysis for hydrogen and cryogenic nitrogen was found to be a potentially viable pathway for green ammonia. The profitability metrics including discounted cash flow rate of return, net present value and discounted payback period were estimated to be 8%, $40 MM, and 4–6 years respectively for this pathway. The cost of electricity, conversion rate, and conversion efficiency dominate the tonnage cost of ammonia and were used to assess the feasibility of the model. A life cycle assessment was also conducted to assess the environmental impact of a well to product ammonia process. • Integrated electrochemical ammonia systems with renewable intermittent sources has. linear scalability advantages. • Energy consumption of at least 17 MWh per metric ton for electrochemical ammonia. • Number of modules decreases with current density. • Specific energy decreases as the production rate increases. [ABSTRACT FROM AUTHOR]

Sensors to detect mixtures of NO x /NH 3 are needed to monitor emissions of diesel automobiles where a selective catalytic reduction system uses an NH 3 mediated reaction to reduce NO x . We report on the application of a three electrode La 0.8 Sr 0.2 CrO 3 , Au 0.5 Pd 0.5 , Pt mixed potential sensor using yttria-stabilized-zirconia (YSZ) as a solid electrolyte to NO x /NH 3 sensing. Artificial neural networks were used to automatically decode the concentrations of NO x /NH 3 and errors of less than 15% are achieved. The optimal architecture for ANN decoding and the maximum density of training data points are also determined. The stability of the sensor was monitored by electrochemical impedance spectroscopy. The impedance associated with YSZ oxygen ion conduction and the electrochemical reactions at the three-phase interface are tracked over a period of over 100 days. [ABSTRACT FROM AUTHOR]

Zirconia-based electrochemical sensors have revolutionized oxygen monitoring and combustion control. These robust, solid-state devices are found in virtually every internal combustion engine today providing feedback information for tight air to fuel ratio control thus minimizing unwanted emissions and improving engine efficiency. Variations on the sensor design and operational mode enable the measurement of nitrogen oxides to part per million levels, providing control information for exhaust after-treatment systems. Emerging designs include the development of "gas analyzers on a chip" capable of monitoring oxygen, carbon monoxide, nitrogen oxides, ammonia and hydrocarbons. • Zirconia based electrochemical gas sensors can detect wide variety of pollutants. • Potentiometric, amperometric, impedance-based, and pulsed polarization methods are reviewed. • Modeling of sensor behavior can predict sensor response. • Machine learning techniques can be applied for sensor signal decoding. [ABSTRACT FROM AUTHOR]

Abstract: In this article, the independent testing and validation of a packaged, electrochemical prototype hydrogen sensor at the National Renewable Energy Laboratory (NREL) is reported. Custom electronics were developed to be compatible with the data acquisition system at NREL. The specialized hydrogen sensor-testing laboratory at NREL used a variety of standardized test protocols to assess sensor performance. The system controlled and monitored humidity, pressure, and hydrogen gas concentration and introduced interference gases such as methane, carbon dioxide, carbon monoxide and ammonia. The hydrogen sensor was made of Indium Tin Oxide and Platinum electrode and Yttria-Stabilized Zirconia (YSZ) electrolyte. NREL testing showed a fast response to H2 with exceptional low-level sensitivity (0.005–2%) and high signal-to-noise ratio. A minimal deviation in sensor response to changes in ambient conditions such as humidity was observed along with minimal response to interference gases. The hydrogen prototype sensor was operational and insensitive to variations in oxygen partial pressure down to approximately 0.2% oxygen, while anaerobic conditions caused the sensor to become inoperable. The NREL tests indicate that the sensor prototype will effectively function and trigger event alarms and continue to function unless anaerobic conditions are established. It is envisioned in future to develop a different working electrode based on a more robust material such as La1−x Sr x CrO3 for applications where substantially harsher environments (absence of oxygen supply, higher altitudes, and higher atmospheric pressure) may be experienced. [Copyright &y& Elsevier]

Highlights: [•] Mixed-potential electrochemical sensors are used to analyze diesel engine exhaust. [•] These sensors exhibit cross-interference between ammonia and hydrocarbons. [•] An array of sensors is created by varying bias currents applied to a single device. [•] Bayesian modeling is employed to infer ammonia concentrations in mixtures with propylene. [•] Minimal data acquisition requirements are investigated. [ABSTRACT FROM AUTHOR]

Abstract: In this article, the influence of perovskite electrode composition on an electrochemical based mixed potential sensor response is reported. Specifically, various stoichiometry of Strontium doped Lanthanum Chromite materials were used as the sensing electrode. Yttria-Stabilized Zirconia was used as the solid electrolyte and Pt as the counter electrode. The effect of varying doping levels of Strontium on the sensor response was studied. NO, NO2, C3H6, and C4H10 were used as test gases. The sensor response was studied under open-circuit and current biased conditions. Based on sensitivity and selectivity evaluations, the device configuration ‘La0.9Sr0.1CrO3/YSZ/Pt’ was found to behave as a selective total hydrocarbon sensor at 500°C when operated under open-circuit conditions. On the other hand, ‘La0.7Sr0.3CrO3/YSZ/Pt’ exhibited minimal cross-sensitivity to hydrocarbons facilitating its use as a selective NO x sensor when operated under a current bias. The variation in the sensor response and selectivity for different electrode materials indicate that it might be possible to develop multi-electrode sensor platform for identifying a suite of analytes with improved selectivity and sensitivity. [Copyright &y& Elsevier]

Abstract: In this investigation, an electrochemical mixed potential type gas sensor was characterized using impedance spectroscopy. Specifically, the effect of operating temperature (435–610°C) on sensor response and response time was studied. Propylene was used as the analyte to test the ‘La0.8Sr0.2CrO3/YSZ/Pt’ sensor configuration. Two-electrode AC impedance measurement was performed with a frequency sweep from 13MHz down to 10mHz and excitation voltage of 10mV. For a fixed propylene concentration, the bulk and interfacial resistances was seen to decrease with increase in the sensor operating temperature. An Arrhenius behavior of the bulk and interfacial resistance was observed. The activation energy for O2 ion conduction and charge transfer was found to be 0.94eV and 1.54eV respectively. For a 150°C rise in operating temperature from 485 to 585°C, a 26-fold improvement in response rise time was observed while an 82% reduction in sensor response was recorded. It is postulated that the increase in operating temperature results in faster reaction kinetics, faster oxygen reduction and greater heterogeneous catalysis. [Copyright &y& Elsevier]

Abstract: In this article, testing of an electrochemical, potentiometric hydrogen safety sensor is reported within a proposed packaging scheme. Device packaging under static and flow testing conditions are presented. During the static volume sensor testing, the sensors response is compared against a calibrated Gas Chromatography (GC) measurement. Also, a commercial H2 sensor is incorporated into the test chamber to act as a benchmark for the sensor prototype. In the testing phase, H2 selectivity is demonstrated using pulsed discharge technique. The packaging schemes for static and flow condition testing permit easy handling and exchange of the laboratory prototype sensors with other agencies for independent testing/performance validation. Upon testing, for a fixed inlet concentration of 2% (20,000 ppm) H2 and within the duration of the typical experiment conducted within a non-sealed test chamber, the sensor sees only around 6200 ppm as confirmed by the GC measurements. The sensitivity is around 105 mV for 6200 ppm of H2. While a logarithmic correlation of the sensor output with H2 concentration is observed in laboratory based H2 sensor, the commercial device suffered from an elevated baseline (due to reduced barometric pressure conditions of 2195 m elevation), humidity and uncorrelated sensor output for different H2 concentrations. The pulsed discharge scheme for achieving hydrogen selectivity holds a great potential for tackling cross-sensitivity problems that affect many H2 sensor technologies. [Copyright &y& Elsevier]

Abstract: The effect of trace quantities of ammonia on oxygen reduction reaction (ORR) on carbon-supported platinum catalysts in perchloric acid solutions is assessed using rotating ring disk electrode (RRDE) technique. The study demonstrates that ammonia has detrimental effects on ORR. The most significant effect takes place in the potential region above 0.7 V vs RHE. The effect is explained by the electrochemical oxidation of ammonia, which blocks Pt active sites and increases the formation of H2O2. This leads to losses in the disk currents and increments in the ring currents. The apparent losses in ORR currents may occur in two ways, namely, through the blocking of the active sites for ORR as well as by generating a small anodic current, which is believed to have a lower contribution. In addition, a detrimental effect of sodium cations in the potential range below 0.75 V vs RHE was demonstrated. This effect is most likely due to the co-adsorption of sodium cations and perchlorate anions on the Pt surface. [Copyright &y& Elsevier]

Abstract: Thermal (gas) nitridation of stainless steel alloys can yield low interfacial contact resistance (ICR), electrically conductive and corrosion-resistant nitride containing surface layers (Cr2N, CrN, TiN, V2N, VN, etc.) of interest for fuel cells, batteries, and sensors. This paper presents results of proton exchange membrane (PEM) single-cell fuel cell studies of stamped and pre-oxidized/nitrided developmental Fe–20Cr–4V weight percent (wt.%) and commercial type 2205 stainless steel alloy foils. The single-cell fuel cell behavior of the stamped and pre-oxidized/nitrided material was compared to as-stamped (no surface treatment) 904L, 2205, and Fe–20Cr–4V stainless steel alloy foils and machined graphite of similar flow field design. The best fuel cell behavior among the alloys was exhibited by the pre-oxidized/nitrided Fe–20Cr–4V, which exhibited ∼5–20% better peak power output than untreated Fe–20Cr–4V, 2205, and 904L metal stampings. Durability was assessed for pre-oxidized/nitrided Fe–20Cr–4V, 904L metal, and graphite plates by 1000+h of cyclic single-cell fuel cell testing. All three materials showed good durability with no significant degradation in cell power output. Post-test analysis indicated no metal ion contamination of the membrane electrode assemblies (MEAs) occurred with the pre-oxidized and nitrided Fe–20Cr–4V or graphite plates, and only a minor amount of contamination with the 904L plates. [Copyright &y& Elsevier]

Abstract: The article details the application of commercial manufacturing methods towards the development of NO x /NH3 sensors for vehicle on-board emissions control. These sensors possess a unique mixed potential sensor design. This unique LANL (Los Alamos National Laboratory) design results in improved sensitivity, selectivity and response time over conventional mixed potential sensors incorporating a stable three-phase interface using a porous electrolyte coated over a dense electrode. A prototype gas sensing platform conducive to large-scale manufacturing and commercialization is also been presented. The observed results indicate the possibility of evolution towards a combined NO x /NH3 sensor on the same platform. Finally, critical challenges towards developing field deployable mixed potential NO x /NH3 sensors are identified and discussed. [Copyright &y& Elsevier]

Abstract: Mixed potential sensors using dense, thin film metal oxide working electrodes, Pt counter electrodes, and thin film YSZ electrolytes on Al2O3 polycrystalline and sapphire substrates were prepared and studied between 450 and 650°C. Their response to NO, NO2, CO, and C1 and C3 hydrocarbons in 10.4% O2/N2 balance and in air atmospheres was characterized. The lanthanum chromite-based sensors showed preferential sensitivity to NO2 with cross sensitivity to CO and non-methane hydrocarbons such as C3H6 and C3H8 with the highest NO x sensitivity and minimal CO/HC cross sensitivity exhibited by a sensor prepared with a La0.8Sr0.2CrO3 working electrode. Studies of the Mg-doped LaCrO3 devices conducted for up to 800h at 600°C showed minimal aging in these devices. In contrast, sensors fabricated with spinel NiCr2O4 or ZnFe2O4 working electrodes showed preferential sensitivity to HCs and minimal sensitivity to NO2. Sensors fabricated with Y0.16Tb0.3Zr0.54O2−∂ working electrodes required operating temperatures in excess of 600°C and, like the spinels, showed minimal NO x sensitivity. A prototype three-electrode mixed potential device for the detection of multiple gases was also demonstrated. The use of a heated Pt black pre-catalyst upstream to the sensor was demonstrated to effectively remove the CO and hydrocarbon response. [Copyright &y& Elsevier]

Thin films of LaCrO3 and La0.8Sr0.2CrO3 were prepared using RF magnetron sputtering, electron beam evaporation and pulsed laser deposition (PLD). The films were prepared from both oxide targets and from targets consisting of Cr metal and lanthanum and strontium fluorides. Subsequent anneal of the fluoride/metal composite films in humidified Ar produced an oxide film. Direct growth of the perovskite from oxide targets via sputtering was usually accompanied by second phases with Cr in valance states higher than 3+. Single-phase La–Sr–Cr–O films could not be prepared from a single oxide target electron beam evaporation. However, thick, stoichiometric films were prepared at 400 °C using an electron beam/thermal evaporation dual source method but inconsistently. Single-phase lanthanum chromate films, based on the limited results obtained in this work, could not be prepared using PLD from either oxide or fluoride precursors under conditions similar to those used in the other techniques. However, films prepared by the intermediate fluoride process via off-axis RF magnetron sputtering process produced high quality thin films with density, microstructure and phase purity very similar to bulk La0.8Sr0.2CrO3 using a film growth temperature as low as ambient (Tsub<100 °C). The deposition rate was typically low at approximately 1500 A˚/h. SEM analysis showed that the morphology of films produced via fluoride sputtering was nearly identical to bulk La0.8Sr0.2CrO3 prepared by sintering ceramic powders at 1650 °C in air and, based on previous work, should be suitable for mixed potential sensor applications. [Copyright &y& Elsevier]