Anode catalytic

A similar infiltration method was used to form anodes with Cu-Co alloys as the electronically conducting phase, with Co added to enhance the anode catalytic activity without catalyzing carbon deposition [85], in contrast with Ni-Cu alloys, which were found to catalyze carbon deposition even when small quantities of Ni were present [86], The authors of the studies [84-86] have reported that the percolation of the infiltrated phases is incomplete following the processing of the cells, such that subsequent carbon deposition can actually serve to connect previously isolated islands of the metallic phase, thus increasing the electronic conductivity and decreasing Rs in the short term. Since carbon deposition was observed by the same authors to cause severe... 

Anodic catalytic waves for hydroquinone were observed at a rotating gold elec-tode, confirming the regeneration mechanism with a rate constant for Phenidone regeneration of 1.3 x 10 L mol s [57]. 

Proton conducting membrane m) Anode catalytic layer mj) Anode diffusion layer cr)... 

Kang Y, Ren M, Yuan T, Qiao Y, Zou Z, Yang H (2010) Effect of Nafion aggregation in the anode catalytic layCT on the ptafonnance of a direct formic acid fuel cell. J Power Sources 195 2649-2652... 

The Wacker anode catalytic cycle, the anode OR, and the cathode and overall cell reactions in this fuel cell eCMR are described below ... 

Another requirement of the underwater power system is the hydrogen-removal system, which is needed to safely remove the hydrogen that is generated by corrosion of the anode. Catalytic recombination is especially attractive for applications where space and energy efficiency are needed. The unit shown in Fig. 38.39 uses a hydrogen-removal system, but the amount of hydrogen generated is not excessive since a low-corrosion aluminum alloy is used. 

In the presence of 6-iodo-l-phenyl-l-hexyne, the current increases in the cathodic (negative potential going) direction because the hexyne catalyticaHy regenerates the nickel(II) complex. The absence of the nickel(I) complex precludes an anodic wave upon reversal of the sweep direction there is nothing to reduce. If the catalytic process were slow enough it would be possible to recover the anodic wave by increasing the sweep rate to a value so fast that the reduced species (the nickel(I) complex) would be reoxidized before it could react with the hexyne. A quantitative treatment of the data, collected at several sweep rates, could then be used to calculate the rate constant for the catalytic reaction at the electrode surface. Such rate constants may be substantially different from those measured in the bulk of the solution. The chemical and electrochemical reactions involved are... 

The methods of investigation of metal species in natural waters must possess by well dividing ability and high sensitivity and selectivity to determination of several metal forms. The catalytic including chemiluminescent (CL) techniques and anodic stripping voltammetry (ASV) are the most useful to determination of trace metals and their forms. The methods considered ai e characterized by a low detection limits. Moreover, they allow detection of the most toxic form of metals, that is, metal free ions and labile complexes. 

In 1996, consumption in the western world was 14.2 tonnes of rhodium and 3.8 tonnes of iridium. Unquestionably the main uses of rhodium (over 90%) are now catalytic, e.g. for the control of exhaust emissions in the car (automobile) industry and, in the form of phosphine complexes, in hydrogenation and hydroformylation reactions where it is frequently more efficient than the more commonly used cobalt catalysts. Iridium is used in the coating of anodes in chloralkali plant and as a catalyst in the production of acetic acid. It also finds small-scale applications in specialist hard alloys. 

Participation in the electrode reactions The electrode reactions of corrosion involve the formation of adsorbed intermediate species with surface metal atoms, e.g. adsorbed hydrogen atoms in the hydrogen evolution reaction adsorbed (FeOH) in the anodic dissolution of iron . The presence of adsorbed inhibitors will interfere with the formation of these adsorbed intermediates, but the electrode processes may then proceed by alternative paths through intermediates containing the inhibitor. In these processes the inhibitor species act in a catalytic manner and remain unchanged. Such participation by the inhibitor is generally characterised by a change in the Tafel slope observed for the process. Studies of the anodic dissolution of iron in the presence of some inhibitors, e.g. halide ions , aniline and its derivatives , the benzoate ion and the furoate ion , have indicated that the adsorbed inhibitor I participates in the reaction, probably in the form of a complex of the type (Fe-/), or (Fe-OH-/), . The dissolution reaction proceeds less readily via the adsorbed inhibitor complexes than via (Fe-OH),js, and so anodic dissolution is inhibited and an increase in Tafel slope is observed for the reaction. 

Degradation of wood is also observed adjacent to anodic corrosion sites. Some metal ions, notably Fe, catalytically decompose the cellulose components of wood. This significantly reduces the wood s fastener-holding ability. 

Thus indeed CH4 oxidation in a SOFC with a Ni/YSZ anode results into partial oxidation and the production of synthesis gas, instead of generation of C02 and H20 as originally believed. The latter happens only at near-complete CH4 conversion. However the partial oxidation overall reaction (3.12) is not the result of a partial oxidation electrocatalyst but rather the result of the catalytic reactions (3.9) to (3.11) coupled with the electrocatalytic reaction (3.8). From a thermodynamic viewpoint the partial oxidation reaction (3.12) is at least as attractive as complete oxidation to C02 and H20. 

Table 3.1 lists some of the anodic reactions which have been studied so far in small cogenerative solid oxide fuel cells. A more detailed recent review has been written by Stoukides46 One simple and interesting rule which has emerged from these studies is that the selection of the anodic electrocatalyst for a selective electrocatalytic oxidation can be based on the heterogeneous catalytic literature for the corresponding selective catalytic oxidation. Thus the selectivity of Pt and Pt-Rh alloy electrocatalysts for the anodic NH3 oxidation to NO turns out to be comparable (>95%) with the... 

The extent to which anode polarization affects the catalytic properties of the Ni surface for the methane-steam reforming reaction via NEMCA is of considerable practical interest. In a recent investigation62 a 70 wt% Ni-YSZ cermet was used at temperatures 800° to 900°C with low steam to methane ratios, i.e., 0.2 to 0.35. At 900°C the anode characteristics were i<>=0.2 mA/cm2, Oa=2 and ac=1.5. Under these conditions spontaneously generated currents were of the order of 60 mA/cm2 and catalyst overpotentials were as high as 250 mV. It was found that the rate of CH4 consumption due to the reforming reaction increases with increasing catalyst potential, i.e., the reaction exhibits overall electrophobic NEMCA behaviour with a 0.13. Measured A and p values were of the order of 12 and 2 respectively.62 These results show that NEMCA can play an important role in anode performance even when the anode-solid electrolyte interface is non-polarizable (high Io values) as is the case in fuel cell applications. 

At t=0 a constant anodic current I=5mA is applied between the Pt catalyst film and the counter electrode. The catalyst potential, Urhe, reaches a new steady state value Urhe=1.18 V. At the same time the rates of H2 and O consumption reach, within approximately 60s, their new steady-state values rH2-4.75T0 7 mol/s, ro=4.5T0 7 mol/s. These values are 6 and 5.5 times larger than the open-circuit catalytic rate. The increase in the rate of H2 consumption (Ar=3.95T0 7 mol H2) is 1580 % higher than the rate increase, (I/2F=2.5T0 8 mol/s), anticipated from Faraday s Law. This shows clearly that the catalytic activity of the Pt catalyst-electrode has changed substantially. The Faradaic efficiency, A, defined from ... 

Since both the forward reactions (9.13) and (9.14) are anodic, it follows that a positive I, causing an increase in catalyst potential Urhe, will also cause an increase in both re,t and re,2, i.e. Are,i>0 and Are,2>0. Consequently, if the rate of the catalytic reaction, rc, were not changing upon current application (Arc=0) it follows from Eq. (9.19) that ... 

Figure 10.2. NEMCA in H2 oxidation on Pt/graphite in 0.1 M KOH Steady-state effect of applied positive (anodic) current (I) on the increase in the rates of hydrogen ( ) and oxygen (O) consumption Ph2=0.8 kPa, po2 L25 kPa r 2 (=rg =rc°)=2,38xl0 7 mol/s is the open-circuit catalytic rate Fv=540 cm3/min at STP. Reprinted with permission from Nature, McMillan Magazines Ltd.3...

Similar electrodes may be used for the cathodic hydrogenation of aromatic or olefinic systems (Danger and Dandi, 1963, 1964), and again the cell may be used as a battery if the anode reaction is the ionization of hydrogen. Typical substrates are ethylene and benzene which certainly will not undergo direct reduction at the potentials observed at the working electrode (approximately 0-0 V versus N.H.E.) so that it must be presumed that at these catalytic electrodes the mechanism involves adsorbed hydrogen radicals. 

Sol-gel technique has also been applied to modify the anode/electrolyte interface for SOFC running on hydrocarbon fuel [16]. ANiA SZ cermet anode was modified by coating with SDC sol within the pores of the anode. The surface modification of Ni/YSZ anode resulted in an increase of structural stability and enlargement of the TPB area, which can serve as a catalytic reaction site for oxidation of carbon or carbon monoxide. Consequently, the SDC coating on the pores of anode leads to higher stability of the cell in long-term operation due to the reduction of carbon deposition and nickel sintering. 

In the search of high-performance SOFC anode, doped ceria have been evaluated as possible anode materials [9,10]. Comparing Ni-samaria-doped ceria (SDC) with Ni-YSZ, the Ni-SDC anode exhibits higher open-circuit voltages and a lower degree of polarization with either methanol as the fuel, as shown in Fig. 5, or methane as the fuel, as shown in Fig. 6. It was found that the depolarization ability of the anode is associated with the catalytic activity, the electrical conductivity, and the oxygen ionic conductivity of the anode materials [9]. It was also found that the anodic polarization and electro-catalytic activity strongly depend on the Ni content in the anode, and the optimum result for the Ni-SDC anode is achieved with 60... 

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