P.J. Mitchell

Methods for the reduction of shape change and dendritic growth in zinc-based secondary cells

Abstract The widespread adoption of alkaline zinc-based secondary systems has been hindered by two inherent problems associated with the charge reaction. These are commonly referred to as shape change and dendrite growth. This review examines the attempts that have been made to lessen their effects and, hence, ultimately arrive at a working, cycleable secondary zinc-based battery.

Electrolyte additives for zinc-anoded secondary cells I. Brighteners, levellers and complexants

Abstract A series of potential dendrite inhibiting additives, used essentially to aid zinc electrodeposition in zinc-anoded secondary cells, has been evaluated. Their performances have been assessed by current-time techniques and typical electrodeposits have been examined both visually and by scanning electron microscopy. Of those additives examined, triethanolamine, polyvinyl alcohol, and those based on heptonate, show promise.

Estimation of the residual capacity of maintenance-free leadacid batteries Part 1. Identification of a parameter for the prediction of state-of-charge

Abstract The ohmic resistance of maintenance-free leadacid batteries has been identified as an ideal parameter for the prediction of the state-of-charge using the a.c. impedance technique. The ohmic resistance has been found to mirror the change in specific gravity of the battery electrolyte when charged or discharged.

Effect of operating pressure on the system efficiency of a methane-fuelled solid polymer fuel cell power source

Abstract The energy conversion efficiency of a fuel cell is directly related to its operating voltage. In general increasing the fuel and oxidant pressure increases the cell potential. However, additional energy is required to compress the gases in order to raise the pressure, negating the efficiency gains achieved in the cells. System designers seek to balance complexity, cost and system efficiency. The overall system efficiency is highly dependent on the interaction and interconnection of the components. For a system which includes a solid polymer fuel cell (SPFC) stack, a methane fuel processor and a compressor/expander an analysis has been carried out to assess the functional relationship between the operating pressure and efficiency. For a system configuration which includes a high-temperature fuel processor and a 40-kW e stack, an 8% improvement in efficiency was predicted for the higher operating pressure (25% for 1.5 bar(a) and 33% for 4 bar(a).

The performance of secondary zinc electrodes in modified alkaline electrolytes I. Galvanostatic passivation studies in alkaline electrolyte

Abstract The passivation characteristics of a planar zinc electrode have been examined in 2 M KOH electrolytes containing a variety of additions. The time to passivation has been measured and compared to that of a planar cadmium electrode in 5.3 M KOH. The most promising additives were found to be borate and chromate. Auger analysis of electrode surfaces revealed possible passivating mechanisms.

Electrolyte additives for zinc-anoded secondary cells II. Quaternary ammonium compounds

Abstract Quaternary ammonium type derivatives have been examined to assess their efficacy as deposit-enhancing agents in secondary zinc-anoded cells. Simple current—time techniques have been utilised to screen potential alkyl groups and examine their effectiveness. Visual assessment and scanning electron microscopy were also applied to examine the zinc electrodeposits. Two promising additives were then further tested by depositing zinc for a set charge to assess their effect on charging time.

The electrodeposition of zinc onto graphitic carbon substrates from alkaline electrolytes

Abstract The electrodeposition and dissolution reactions of zinc on both solid and pasted graphitic substrates, in a series of KOH electrolytes containing zincate, have been studied using cyclic voltammetry. The data acquired have been used to aid the interpretation of the effects of graphitic additions on the charge and discharge reactions of conductor-modified secondary cells with zinc anodes.

The electrotechnology of the nickel positive electrode: a review of the recent literature

Abstract A review is presented of the very recent electrotechnology of the nickel positive electrode. The majority of the literature covered is from the 1980s and 61 references are noted.

Prospects for the application of fuel cells in electric vehicles

Abstract For a hybrid vehicle the use pattern has large effect on the vehicle design. If the vehicle is to be used extensively on the motorway then a continuous high power is required. For the case of a fuel cell battery hybrid vehicle this would require a large fuel cell ( > 30 kW) to meet the sustained high power demand. The current high materials and fabrication cost of most fuel cells prohibits the commercial development of such a system. Consequently if fuel cell vehicles are to enter a ‘clean car’ market, earlier rather than later, alternative configurations must be sought and compromises in terms of performance are inevitable.

The electrodeposition of zinc from zincate solutions. A review

The costly effluent disposal of alkaline cyanide-based electrolytes coupled with more stringent pollution laws has led to the appraisal of possible alkaline alternatives for the electrodeposition o...