Mid Sweden University

A system for the measurement of methane concentration in water is presented. The system is a stand- alone device using a high-resolution NDIR (Non-Dispersive Infra-Red) gas sensor. The NDIR sensor is configured to measure methane, water vapor, and carbon dioxide in the air. It is mounted in a housing with a stabilized environment and includes cross-sensitivity compensation. An equilibrator is used to transfer the methane concentration from the water into a circulating gas flow that is analyzed by the NDIR gas sensor. The equilibrator consists of a vertical plastic tube filled with 2,000 glass marbles, where the water runs from top to bottom on the surface of the glass marbles, in contact with a circulating air flow, exchanging gas. The system is stand- alone, including power supply and logging features for 72 hours of operation. The system performance was evaluated in a field test, measuring the methane content of seawater at a fiber bank in Sundsvall, Sweden. This fiber bank consists of remaining waste from an old paper industry from before 1970 and is known to produce methane. The detection limit of the tested system is below 1.4 nmol/L in water, corresponding to 1 ppm methane concentration in the air. The settling time of the system in its current configuration, including the equilibrator and gas sensor housing, is 30 minutes. 

Measurements of atmospheric gas concentrations using of NDIR gas sensors requires compensation of ambient pressure variations to achieve reliable result. The extensively used general correction method is based on collecting data for varying pressures for a single reference concentration. This one-dimensional compensation approach is valid for measurements carried out in gas concentrations close to reference concentration but will introduce significant errors for concentrations further away from the calibration point. For applications, requiring high accuracy, collecting, and storing calibration data at several reference concentrations can reduce the error. However, this method will cause higher demands on memory capacity and computational power, which is problematic for cost sensitive applications. We present here an advanced, but practical, algorithm for compensation of environmental pressure variations for relatively low-cost/high resolution NDIR systems. The algorithm consists of a two-dimensional compensation procedure, which widens the valid pressure and concentrations range but with a minimal need to store calibration data, compared to the general one-dimensional compensation method based on a single reference concentration. The implementation of the presented two-dimensional algorithm was verified at two independent concentrations. The results show a reduction in the compensation error from 5.1% and 7.3%, for the one-dimensional method, to −0.02% and 0.83% for the two-dimensional algorithm. In addition, the presented two-dimensional algorithm only requires calibration in four reference gases and the storing of four sets of polynomial coefficients used for calculations. 

A selective algorithm for nondispersive infrared (NDIR) sensing of gases with overlapping absorption spectra was developed and evaluated in modified multichannel NDIR sensor. Measurements in the optic channel with the spectral band where two gas species (target and secondary gas) have overlapping absorption lines are complemented by additional measurements in second channel where spectral absorption for only one gas (secondary gas) is present. The real concentration for the target gas is retrieved by adjusting the absorption data obtained in the overlapping gas spectra's optic channel, with respect to the absorption data retrieved in the second optic channel that has sensitivity only for the secondary gas. An implementation example is performed by obtaining the true concentration of CH4 (as target gas) in a mixture with H2O vapor. The channel for the target gas is equipped by an optic filter with spectra at 3.375 μm where both CH4 and H2O have absorption lines. The complementary second channel provides sensing in spectra at 2.7 μm where only H2O have absorption. Data from a third channel, at 3.95 μm, is used as reference value for 'zero-level' calibration. A calibration procedure was developed and tested, which involves matching of the absorbed light energy in target and secondary channels in humid reference environments. A selective algorithm for sensing of CH4 with elimination of spectral impact from H2O was validated in environments with variable CH4 and H2O concentrations. By implementing the multispectral approach and the developed algorithm, an uncertainties of 5-10 ppm relative the reference concentrations were achieved. For the environments where selective algorithm was validated this should be compared to an uncertainty of 70-90 ppm for the non-corrected CH4 concentration. 

A multispectral nondispersive infrared (NDIR) sensor was developed for simultaneous detection of methane and water vapor in air. The NDIR sensor is capable of measuring optic transmission in the CH4 absorption spectra at 3.375 μm and the H2O absorption spectra at 2.7 μm. Data from a third channel, 3.95 μm, is used as reference value for 'zero-level' calibration. The actual CH4 concentration is retrieved by adjusting the data obtained in the CH4 spectra with respect to the concentration sensed in the H2O spectra. A calibration procedure was developed and tested, which involves matching of the absorbed light energy in the CH4 and the H2O spectrum in humid reference environments. A compensation algorithm for elimination of humidity impact was developed and validated in environments with variable CH4 and H2O concentrations. By implementing the multispectral approach, and the developed algorithm, an uncertainty of 15-25 ppm relative the reference concentrations was achieved. For a concentration range valid for environmental monitoring applications this should be compared to an uncertainty of 180-200 ppm for the non-corrected CH4 concentration. 

This paper presents a lab test system for studying pressure dependence of NDIR gas sensors in accuracy demanding applications. The test system consists of a hardware test bench, user software (LabVIEW based) and a calculation algorithm. The lab test bench provides highly accurate test environment for collecting characterization data. The software and the calculation algorithm process the data to derive accurate compensation parameters for each specific design of NDIR sensors. The compensation parameters are used to normalize the measured concentration to the values valid for standard atmospheric pressure.

Printed electronics is a rapidly developing field where many components can already be manufactured on flexible substrates by printing or by other high speed manufacturing methods. However, the functionality of even the most inexpensive microcontroller or other integrated circuit is, at the present time and for the foreseeable future, out of reach by means of fully printed components. Therefore, it is of interest to investigate hybrid printed electronics, where regular electrical components are mounted on flexible substrates to achieve high functionality at a low cost. Moreover, the use of paper as a substrate for printed electronics is of growing interest because it is an environmentally friendly and renewable material and is, additionally, the main material used for many packages in which electronics functionalities could be integrated. One of the challenges for such hybrid printed electronics is the mounting of the components and the interconnection between layers on flexible substrates with printed conductive tracks that should provide as low a resistance as possible while still being able to be used in a high speed manufacturing process. In this article, several conductive adhesives are evaluated as well as soldering for mounting surface mounted components on a paper circuit board with inkjet printed tracks and, in addition, a double sided Arduino compatible circuit board is manufactured and programmed.

The physical and electrochemical properties of ternary oxides Ti 0.7Ru0.3-xCoxO2 (x = 0.093 and x = 0) have been investigated and compared. Samples of three different thicknesses were prepared by spin-coating onto polished titanium to achieve uniform and well-defined coatings. The resulting electrodes were characterized with a variety of methods, including both physical and electrochemical methods. Doping with cobalt led to a larger number of micrometer-sized cracks in the coating, and coating grains half the size compared to the undoped samples (10 instead of 20 nm across). This is in agreement with a voltammetric charge twice as high, as estimated from cyclic voltammetry. There is no evidence of a Co 3O4 spinel phase, suggesting that the cobalt is mainly incorporated in the overall rutile structure of the (Ti,Ru)O2. The doped electrodes exhibited a higher activity for cathodic hydrogen evolution compared to the undoped electrodes, despite the fact that one third of the active ruthenium was substituted with cobalt. For anodic chlorine evolution, the activity was similar for both electrode types.

Substrates of different roughness spin coated with Ti0.7Ru 0.3O2 films have been evaluated as model system for fundamental studies of the industrially and scientifically interesting (Ti,Ru)O2 based electrodes. The approach allowed for much more accurate control over the material synthesis than the traditionally used brush-, dip-, or spray-coating, on titanium-metal substrates. It moreover yielded well-defined samples suitable for basic studies of the surface properties that are of fundamental importance for understanding the electrochemical functionality of the electrode. We have compared the films on silicon substrates to films prepared by spin coating the same material on titanium-metal substrates. Samples have been characterized using atomic force microscopy (AFM), X-ray diffraction, scanning electron microscopy (SEM), and cyclic voltammetry. The samples displayed a uniformity of the films appropriate for AFM characterization. The smoother the substrate the less cracks in the coating. Using easily broken silicon wafers as substrate, a straightforward sample preparation technique was demonstrated for cross-section SEM. In addition, using high spinning velocities we have deposited the oxide films directly on silicon-nitride grids, thin enough to allow for studies with transmission electron microscopy without further sample preparation.

Activation of the hydrogen evolution reaction (HER) by in-situ addition of Mo(VI) to the electrolyte has been studied in alkaline and pH neutral electrolytes, the latter with the chlorate process in focus. Catalytic molybdenum containing films formed on the cathodes during polarization were investigated using scanning electron microscopy (SEM), energy-dispersive X ray analysis (EDS), X-ray photoelectron spectroscopy (XPS), and X ray fluorescence (XRF). In-situ addition of Mo(VI) activates the HER on titanium in both alkaline and neutral electrolytes and makes the reaction kinetics independent of the substrate material. Films formed in neutral electrolyte consisted of molybdenum oxides and contained more molybdenum than those formed in alkaline solution. Films formed in neutral electrolyte in the presence of phosphate buffer activated the HER, but were too thin to be detected by EDS. Since molybdenum oxides are generally not stable in strongly alkaline electrolyte, films formed in alkaline electrolyte were thinner and probably co-deposited with iron. A cast iron molybdenum alloy was also investigated with respect to activity for HER. When polished in the same way as iron, the alloy displayed a similar activity for HER as pure iron.

Sodium chlorate is mainly used for production of chlorine dioxide (a pulp bleaching agent). Sodium chlorate is produced by an electrochemical process where chloride ions (from sodium chloride dissolved in water) are oxidized to chlorine on the anodes and hydrogen is evolved on the cathodes. The anode of this process consists of a metal plate coated with a catalytically active metal oxide film. The electrocatalytic properties of the anode coating film have been widely investigated due to the great importance of these electrodes in the electrochemical industry. The material properties are, however, not as well investigated, and the studies described in this thesis are an attempt to remedy this.

Several standard material characterization methods were used, such as SEM, TEM, AFM, EDX, XRD, porosimetry and DSC. Also, a novel model system based on spin coated electrode films on smooth substrates was developed. The model system provided a way to design samples suitable for e.g. TEM, where the sample thickness is limited to maximum of 100 nm. This is possible due to the ability to control the film thickness by the spinning velocity when using the spin coating technique.

It was shown here that the anode coating has a nanostructure. It consists of grains, a few tens of nanometers across. The nanostructure leads to a large effective area and thus provides an explanation of the superior catalytic properties of these coatings. The grains were also shown to be monocrystalline. The size of these grains and its origin was investigated. The calcination temperature, the precursor salt and (if any) doping material all affected the grain size. A higher calcination temperature yielded larger grains and doping with cobalt resulted in smaller grains and therefore a larger real area of the coating. Some preparation conditions also affected the microstructure of the coating; such as substrate roughness. The microstructure is for example the cracked-mud structure. A smoother substrate gave a lower crack density.

The cathode of chlorate production is usually an uncoated metal plate, therefore 'less catalytically active'. It is, however, possible to activate the cathode by for example in situ additions to the electrolyte. It was shown here that sufficient addition of molybdate to the electrolyte resulted in a molybdenum film deposited on the cathode and thereby an increase of its surface area and an activation the hydrogen evolution reaction.