Tadahiko Mizuno, Jed Rothwell, in Cold Fusion, 2020
Reactants
Nickel mesh and deuterium gas were used as reactants. The hydrogen molecules of the reactant are dissociated into hydrogen atoms and incorporated into the metal. The nickel mesh was plated with palladium (200 mesh, 200 × 300 mm, for 2 pieces with a total weight of 36 g). When the palladium temperature exceeds 300°C, the hydrogen content cannot be increased further because hydrogen exits from the metal, but the metal is extremely active with hydrogen gas. As the temperature of nickel increases, the solubility of hydrogen gas into the metal increases, so excess heat generation at high temperatures becomes easier. To generate excess heat via cold fusion, surface refinement of the reactant metal, impurity removal, and surface modification with other metals are needed. An outline of these treatments is given below.
In a first setup, Mizuno [14] measured excess heat by plasma sputtering palladium on a nickel mesh. He then introduced deuterium and checked the amount of excess heat vs temperature by air flow calorimetry. Excess heat from 10 to 40 W were measured.
In a second design, Mizuno et al. [15] have produced excess heat by depositing palladium on a nickel mesh, either by rubbing a palladium rod onto the mesh, or by electroless plating, see Fig. 11 for details of the setup. The excess power measured by airflow calorimetry was 10–30 W, or 5%–15% of input power, and up to 40 W in one instance. More details of this work is in Chapter 8.
Fig. 11. Schematic representation of the second setup.
A major influence of electrode structure on cell voltage was observed with the static cell. Figure 6.27 shows the cell voltage data obtained for two different designs, namely nickel mesh on the stainless steel feeder plate, and then with the feeder plate only. The conditions for the experiment were: electrolyte, 7.7 M KOH solution, electrode spacing 2 mm. As can be seen from Figure 6.27, at a solution bulk temperature of 348 K, with a current density of less than 10 kA/m2 there were no significant voltage differences between the two electrode structures. However, notable differences were apparent when the current density was higher than10 kA/m2. This behaviour was attributed to (a) the different electrode material, and (b) the extra surface area conferred by the nickel mesh. These factors obviously became more critical as the rate of bubble generation increased. It was presumed that the effect would be observed at lower current densities if smaller electrode spacing had been used.
Figure 6.27. Cell voltage against current density for the static cell for different electrodes. The conditions for the experiment were as follows: electrolyte, 7.7 M KOH solution; bulk temperature, 348 K; inter-electrode space, 2.0 mm. Square solid dots represent the experiment data for electrodes made of nickel mesh upon stainless steel current feeding plate, and triangular solid dots for electrodes made of stainless steel current feeding plate only.
Further tests were performed to check the effect of additional electrode area. Figure 6.28 shows data obtained with electrodes comprised of different numbers of nickel mesh layers. Under the conditions used previously, the cell voltage tended to reduce with increased numbers of mesh layers at any given current density, though the effect was most marked at high current density. This result shows that high electrode areas are conducive to improved cell efficiency. However, with only gravitational acceleration available, this approach could be self-defeating due to the increased gas logging encountered with what effectively becomes a porous electrode.
Figure 6.28. Cell voltage versus current density for the static cell with electrodes comprising different number of nickel mesh layers. The conditions for the experiment were as follows: electrolyte, 7.7 M KOH solution; bulk temperature, 348 K; inter-electrode space, 2.0 mm. Square solid dots represent the experiment data for electrodes made of one layer of nickel mesh upon stainless steel plate; triangles for electrodes of two layers nickel mesh upon stainless steel plate; and round solid dots for electrodes of three layers nickel mesh upon stainless steel plate.
Three types of the cathode, mesh-like stainless steel, nickel, and copper (S1, S2, and S3), respectively, were used, and the following conclusion was drawn:
1.
Compared with stainless steel and copper meshes, nickel mesh cathode remarkably affected the reactor performance by showing promising results in COD with a maximum value of 84.56%, TOC removal efficiency of 83%.
2.
Carbohydrate removal was not significantly affected by the cathode material, MY raised to a maximum of 0.143 mL/mg COD and MPR to 0.37 m3 CH4/m3 reactor/day in S2 reactor, with a current generation of 8.6 mA.
3.
CV analysis of the cathode materials showed significant peaks, which indicated the low overpotential and high current generation of nickel. The CE values were relatively less, and we suggest that increasing the electrode size and surface area may bring about a rise in energy efficiency.
4.
In-depth microbial community analysis is also needed to support the role of microbes in this study.
In Japan, Fuji Electric demonstrated a 10 kW AFC (1972). Around 1976, Elenco, a Belgian–Dutch consortium, built fuel cell stacks of 24 monopolar alkaline cells (for cell characteristics, see Figure 6). The hydrogen and oxygen electrodes were based on nickel mesh. At the electrolyte side, a layer of activated carbon–PTFE–platinum was rolled on, and at the gas side, a layer of porous PTFE. Heat treatment or sinter processes were not required. The electrodes were mounted in injection-molded acrylonitrile butadiene styrene plastic (ABS) frames. The electrolyte of potassium hydroxide was ‘mobile’, that is, it was circulated in the gaps between the electrodes. In the later EUREKA project (1989–94), together with Air Products, Ansaldo, and Saft, an 80 kW fuel cell system fueled by LH2 was combined with a nickel–cadmium battery in a 180 kW/800 V propulsion system for city buses.
Figure 6. Current–voltage characteristics after the data of Elenco alkaline fuel cells (6.6 mol L−1 KOH, 70 °C): 1 = H2/O2 (platinum), 2 = H2/air (platinum), 3 = H2/air (without catalyst). A = activation polarization, B = ohmic drop in the electrolyte, C = mass transport controlled region at high current densities. Reproduced from Kurzweil P (2003)Brennstoffzellentechnik (Fuel Cell Technology). Wiesbaden: Vieweg.
In this case study, H2 and N2 are directly used for electrochemical synthesis of ammonia at the electrodes. N2 receives the electrons from external power supply. Hence nitrogen gas sent via the porous nickel cathode is reduced to nitride according to the following equation:
(2)
It becomes N3− then after moves to the other electrode where H2 is being supplied. Hydrogen ions combine with nitrogen ions and form NH3 at anode electrode as illustrated in Fig. 30 and shown the following equation:
Fig. 30. Electrochemical ammonia synthesis reaction in molten salt medium.
(3)
The anode reaction is also achieved on porous nickel electrode.
The overall reaction is:
(4)
Hydrogen and nitrogen are required separately to be produced and supplied to the ammonia synthesis reactor. To conduct the electrochemical reaction for ammonia synthesis, reactant nitrogen is supplied from the nitrogen tank. For the production of hydrogen, a separate electrode–electrolyte assembly is formed consisting of graphite rods and NaOH electrolyte. The volume of the electrolyte is 1 L whereas the molarity of NaOH solution is 1 M.
Nickel mesh is used for both electrodes each having an area of 100 cm2 as shown in Fig. 31. Nickel meshes have high melting point, non-corrosivity, high conductivity and excellent stability in the molten salt medium. The area of 100 cm2 is used for Faradaic efficiency calculations. The reactor, 500 mL crucible, is made of Alumina (Al2O3) being 99.6% pure, having high melting point, strong hardness, chemical stability, and non-corrosivity. The cover plates are made of stainless steel (316 alloys) which withstand high temperatures.
Fig. 31. Nickel mesh electrodes in the reactor for the reactor.
The molten salt electrolyte is a mixture of 0.5 M NaOH and 0.5 M KOH. The mass of the NaOH is 221 g whereas KOH mass is 310 g. The total volume of the mixture was about 430 mL at 200°C. The mixture is originally prepared at room temperature, putting the salts into the reactor to melt in the crucible when initially heated up to 255°C. The experiments were performed at 210 and 215°C using the heating tape shown in Fig. 32.
Fig. 32. Heating tape used around the alumina crucible.
Iron oxide (Fe3O4) as nano-powder (20–30 nm, 98+%) is used in the experiments as a catalyst. The high surface area of the nano-Fe3O4 in the electrochemical synthesis is critical for the reaction to occur and to obtain higher ammonia evolution rates. Since ammonia is highly soluble in water, the molten salt electrolyte is not mixed with the water inside the reactor to allow higher ammonia capturing in the H2SO4 solution.
The ammonia electro-synthesis chamber comprises a nickel mesh cathode and a nickel mesh anode immersed in molten hydroxide electrolyte containing 10 g suspension of the nano-Fe3O4 contained in alumina crucible sealed to allow gas inlet at the cathode and gas outlet from the exit tubes. The reactants, H2 and N2, are bubbled through the mesh over the anode and cathode, respectively. The combined gas products (H2, N2, and NH3) exit through two exit tubes in chamber head space. The exiting gasses are firstly measured using flow meters and bubbled through an ammonia water trap then analyzed for ammonia, and subsequently, the NH3 scrubbed-gas is analyzed for H2 or N2 using hydrogen analyzer device (ABB Continuous gas analyzers model AO2020). In the alumina crucible cell, the anode consists of a pure Ni mesh with an area of 100 cm2 and the 100 cm2 cathode composed of the same material. These Ni meshes are stable in the molten 200–250°C hydroxide. The electrodes are connected externally by spot welded Ni wires. The reactor is kept at constant temperature using on/off type temperature controller, and the internal temperature of the reactor is continuously measured using a Pt 100 temperature probe inside the reactor body. As mentioned earlier, the product gasses from the reactor is bubbled through an ammonia trap consisting of a dilute 500 mL 0.001 M H2SO4 solution, changed every 15 min for ammonia analysis. Ammonia concentration is determined using various techniques to confirm the results. The methods utilized are as follows: ammonia test strips, ammonia gas flowmeters, Arduino ammonia gas sensor, and salicylate-based ammonia determination method. For the salicylate-based method, two different solutions are used where one of them contains sodium salicylate, and the other one contains sodium hydroxide and sodium hypochlorite. In each case, redundant measurements yield similar ammonia formation values, with the observed reproducibility of methodologies. Also, the pH level of the dilute H2SO4 solutions is recorded before and after NH3 trapped in the solution in order to observe the dissolved ammonia. Ammonia formation rate is calculated by converting the measured NH3 to moles per seconds and considering the surface area of Ni electrodes as 100 cm2. The ammonia formation rate is calculated using the following equation:
(5)
where [] is the concentration of formed ammonia in mg/L, is the total volume of H2SO4 for trapping ammonia as L and is the time of collection.
The Faradaic efficiency is calculated based on the moles of electrons consumed compared to the 3e−/NH3 equivalents produced. Thus, the Faradaic efficiency of ammonia generation process is defined as follows:
(6)
where F is Faraday constant and is the current density (A/cm2).
The energy efficiency of the ammonia production process is also calculated based on lower heating values (LHVs) of reacted hydrogen and ammonia, nitrogen enthalpy and electrical power input as follows:
(7)
where is the total electricity input during the experiment calculated using the total charge, applied voltage and duration.
Planar, also known as flat plate, SOFCs are more popular than the tubular type of SOFCs because they are easy to fabricate, operate at a lower temperature, and offer a higher-power density [14]. A typical unit cell in a planar SOFC is made of a positive electrode–electrolyte–negative electrode, also called PEN, assembly, a porous nickel mesh, two end interconnect plates and gas seals, as shown in Fig. 2.1. As can be seen, in a planar SOFC-type configuration, the electrolyte layer is sandwiched between anode and cathode layers. In some collector plates, the air and fuel is supplied through the channels that are embedded in the cell flat plate. This design reduces the Ohmic resistance and gives higher-power densities compared to tubular type of SOFC.
Figure 2.1. Schematic of a planar-type SOFC.
Another advantage of the planar-type SOFC is its simple design and low-cost fabrication method such as screen printing and tape casting that reduces the manufacturing costs. Planar substrate is normally fabricated by tape casting and other components are doped on the surface by screen printing, and/or laminating process.
One of the major disadvantages of planar design is the reactants leakage through the cell edges, requiring gas-tight sealing. The sealing material must not only seal the edges of the cell and avoid fuel leakage and air mixing but also be mechanically compatible (i.e., must match the coefficient of thermal expansions with adjacent components) and chemically stable (i.e., long-term stability under the RedOx environment). Glass ceramics and glass are materials that are used for preventing the leakage in planar-type SOFCs [15].
To optimize the use of MH as active material in the NiMH cells, a great effort has been made to develop MH electrode technology. The aim of the MH electrode technology is to make MH electrodes possess an appropriate energy capacity, suitable geometric dimensions, good mechanical integrity, satisfactory electrochemical functioning, and long cycle life. At present, two different techniques for preparing MH electrodes have been developed and are widely used in the battery industry: (i) the sintering method (Fetcenko et al. 1990) for Ti-Zr-V-based alloy by pressing the powder materials without additive on a nickel-mesh sheet, followed by a sintering process; and (ii) the pasting method (Kinoshita et al. 1996) by extruding the substrate through a slurry containing MH powder, conductive powders such as carbon, nickel, cobalt, etc., and other additives to improve the electrode conductivity and surface reactivity. The pasting technology is more complicated because the properties of the numerous additives have to be optimized to obtain the desired electrode properties. The binder materials, such as polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), silicon rubber, SEBS rubber, etc. have been characterized for use in the MH electrode to obtain satisfactory mechanical strength; additives like carbon black will form a solid–gas interface to accelerate the oxygen recombination; a hydrophilic agent may generate a solid–liquid interface to enhance the water electrolysis, etc.
A significant improvement in electrode technology, for both MH and Ni(OH)2 , allows improvement in the packing factor of the active materials without sacrificing the electrochemical efficiency, and in turn improves the NiMH energy density (see Table 1). Since 1991, NiMH batteries have become an important part, with growing potential, of rechargeable batteries and a well-developed new industrial domain, including manufacturing of raw materials and component parts around the NiMH batteries, has been established.
Table 1. Examples to show the progress of a NiMH cell capacity (in mAh).
The cell tests were performed in the Energy Research Center (Petten, the Netherlands) in a test bench with an alumina housing for 5 × 5 cm2 cells [127].
Fuel cells were assembled in configuration Pt grid/LSC/20GCO/8YSZ/Ni-YSZ anode substrate/Ni-Al foam catalytic plate/Ni grid. Here, platinum grid was used for cathode current collection, LSC is cathode La-Sr-cobaltite layer, and 20GDC-Ce0.8Gd0.2O2 − y interlayer is between cathode and a thin layer of YSZ supported on a planar Ni-YSZ anode substrate. Nickel mesh as anode current collector was pressed to Ni-Al foam catalytic plate, so current was passed through it. A stream of CH4 + H2O feed (H2O/CH4 = 2) or humidified H2 was passed along the catalytic plate loaded with 5 wt% of nanocomposite 50% LaMnCrPr + 30%NiO + 20%YSZ promoted by 1.3 wt% Ru. Air stream was used as oxidant from the cathode side. Electrochemical characterization was performed by V/I curves and impedance spectroscopy with a Solartron 1255/1287 setup.
At 600°C and 700 mV, the area-specific resistance (ASR) was estimated to be 0.77 ohm cm2 without any contribution of catalyst to Rohm, which meets target of operation for intermediate-temperature solid oxide fuel cells.
As follows from Fig. 12.26, 800°C cell performance for both types of fuels is comparable, which demonstrates a high efficiency of planar catalytic element in steam reforming of methane. Power density up to 350–850 mW cm− 2 is achieved in 600–800°C range, which is comparable with best values reported in literature (Table 12.14) and is promising for the practical application. At CH4 flow of 90 mL min− 1 and 600°C CH4, conversion increases from 47% to 55% with increasing current from 0 to 4 A, which suggests impact of direct electrochemical oxidation of methane in this cell.
Fig. 12.26. Power-current density characteristics of the 25 cm2 SOFC with Ni-Al foam-supported nanocomposite catalyst at 800°C, 700°C, 600°C, and 605°C measured at 500 cm3 min− 1 flow rate of H2 or 130, 100, and 90 cm3 min− 1 flow rate of CH4·H2O/CH4 = 2.
Cyclic voltammetry is a convenient method to study redox reactions which occur in a specified range of potential. Three types of electrode cell consisting of working, counter and reference electrodes are normally used, as shown in Fig. 1. The working electrode is a carbon material. When the carbon material is in sheet or block form, it is easy to use as an electrode. For powder carbons, it is bound onto a foamed nickel surface using a binder such as polyvinylidene fluoride (PVDF) [5] or pressed onto nickel mesh. In order to characterize a carbon for use as an anode of the lithium ion secondary battery, metallic lithium is employed as the counter and reference electrodes in organic solvents. They are prepared by pressing metallic lithium onto a nickel mesh. When highly crystalline graphite is used as an electrode material, a mixture of ethylene carbonate (EC) with either diethyl carbonate (DEC) or dimethyl carbonate (DMC) (1:1 in volume) containing 1 mol dm−3 LiClO4 or LiPF6 should be employed. Of these, EC is an essential component in the solvents because EC decomposes electrochemically to form a thin protective film on the graphite surface so preventing degradation of the graphite during charge/discharge cycling [6]. On the other hand, when a non-graphitic carbon is used, propylene carbonate (PC) containing solvents is preferable for the formation of this surface film. In commercial batteries, LiPF6 is used as an electrolyte to avoid explosions. However, LiClO4 is used in laboratory experiments because of its relatively high solubility in organic solvents. The electrochemical cell is placed in a glove box filled with dry argon gas. The glove box is thermostatted to about 25°C.
Fig. 1. Schematic illustration of an electrochemical cell.
The electrode potential of the working electrode is measured relative to that of a lithium reference electrode, vs Li/Li+, through a Luggin capillary used to reduce errors (usually several tens mV) caused by an IR drop in solution. If the error is not important, then the Luggin capillary is not used. Three electrodes are connected to a potentiostat/galvanostat. In cyclic voltammetry experiments, the electrode potential is scanned in a negative direction from the rest potential (≈ 3 V for a carbon material) and reversed at 0 V vs Li/Li+ by a function generator and potentiostat/galvanostat. After the potential reverse, the potential is scanned in a positive direction and again reversed at a desired positive potential. Potential scans are usually repeated between 0 and 1–3 V vs Li/Li+ depending on the kind of experiment or carbon material used. The scan speed is changed in the range of 0.1 mV s−1–100 V s−1. Slow scan speeds of 0.1–1 mV s−1 are close to a steady-state method. Current flow during a potential scan is recorded on a chart of an X–Y recorder as a function of the potential of the working electrode. In cyclic voltammetry experiments, a cyclic voltammogram, as shown in Fig. 2, is obtained. The horizontal and vertical axes show the potential of the working electrode and current flow during a potential scan, respectively. Two cathodic peaks and the corresponding anodic peaks are usually observed. Peak current, ip, increases as the reaction rate increases. When the rate of charge transfer is much faster than rates of diffusion of a reactant or a product, then the peak current ip is proportional to v1/2 (v: scan speed). When the rate of charge transfer is comparable to or slower than rates of diffusion, the rate of charge transfer becomes faster as the scan speed decreases. When the scan speed is sufficiently high, the rate of charge transfer, relatively, is much slower than rates of diffusion. In this case, values of ip are also proportional to v1/2, but are not proportional to v1/2 in an intermediate condition. It is also found that the potential difference between anodic and cathodic peaks, ΔEp (= Ea – Ec) decreases as the rate of charge transfer increases. When several reactions occur at different potentials, the same number of corresponding peaks is usually observed. Figure 3 shows an example of a cyclic voltammogram for graphite powder (average particle diameter 7 μm) obtained at 0°C in 1 mol dm−3 of LiClO4-EC/DEC. On the first scan in the cathodic direction, a small peak is observed at 0.6–0.7 V, indicating the electrochemical reduction of EC. Further reduction of graphite yields two peaks at ca. 0.15 V and nearly 0.0 V, which are regarded as the formation of stage 2 and 1 lithium-intercalated graphite, respectively [7]. With anodic oxidation, two peaks corresponding to those observed on the cathodic side appear at ca. 0.12 and 0.28 V. The two cathodic and anodic peaks show the reversible intercalation and de-intercalation of lithium. From the second cycle, only anodic and cathodic currents for lithium intercalation/de-intercalation are observed.
Fig. 2. A cyclic voltammogram.
Fig. 3. Cyclic voltammogram for a graphite powder (≈7 μm) obtained in 1 mol dm−3 LiClO4-EC/DEC at 0°C. Dashed line: 1st cycle; solid line: 6th cycle.
Recently, a new compact apparatus for cyclic voltammetry experimentation was developed. The three parts of the experimental system are accommodated in one apparatus which is conveniently operated by a computer system. It is now commercially available.