Electrolyzer efficiency

In order to maximize electrolyzer efficiency, the available solar energy has to be equally distributed by the power controller (PoC-2) among the cell electrodes and the rate of electrolyte circulation has to be matched to the electrolyzer loading. The other contribution to efficiency is minimizing pumping costs, which is achieved by the use of variable-speed pumps and by circulating only as much electrolyte as the power distribution controller (PoC-2) requires to maximize efficiency. 

It should be noted that much progress is being made in the use of catalysts in fuel cells and electrolyzers. In both the cost and supply of fuel cells, the need for platinum catalysts used to be a serious limitation because platinum is expensive and its availability is limited. This limitation is being solved by the development of nanocarbon catalysts. Similarly, in the area of electrolyzer efficiency the new NanoNi catalysts promise a more than doubling of the H2 output of electrolyzers by drastically increasing the electrode surfaces (QuantumSphere, Inc.). 

Figure 5.1.6 Comparison of the energy efficiencies and current densities for C02 reduction to formic acid, syngas, and hydrocarbons (methane and ethylene) reported in the literature with those of water electrolyzers. Efficiencies of electrolyzers are total system efficiencies, while the CO2 conversion efficiencies only include cathode losses and neglect anode and system losses. Adapted from [17],...

An initial cost analysis was completed in [56] to determine the effects of the electricity price on hydrogen costs. For each electrolyzer, the specific system energy requirement was used to determine how much electricity is needed to produce hydrogen. At current electrolyzer efficiencies, in order to produce hydrogen at lower values than US 3.00/kg, electricity costs must be lower than 4//kWh. In a developing country without oil, such as Uruguay, the electricity costs from thermal devices are nearly US 1/kWh, so the inferences have to be very different. 

Hydrogen production costs from electrolysis are highly dependent on electricity prices (Table 6.7). For an electrolyzer efficiency of 70%, each 1-cent increase in electricity prices raises the produced hydrogen cost by 0.47 /kg. At the average price paid for electricity by residential users in 2003 (8.97cents/kWh ), it would cost about 4.44 /kg to produce... 

Cell room current efficiency should be determined at least twice a week. In a bipolar cell room with a relatively small number of electrolyzers, individual electrolyzer efficiencies should be measured weekly. If individual sample connections are available, the current efficiency of a single cell can be determined. 

The electrolyzer efficiency is the reverse of fuel cell efficiency ... 

Depending on their conversion efficiency, electrochemical detectors can be divided into two categories those that electrolyze only a negligible fraction (0.1-5%) of the electroactive species passing through the detector (amperometric detectors), and those for which the conversion efficiency approaches 100% (coulo-metric detectors). Unfortunately, the increased conversion efficiency of the analyte is accompanied by a similar increase for the electrolyte (background) reactions, and no lowering of detection limits is reahzed. 

V) is actually required to electrolyze water when platinum electrodes are used. Much contemporary research on electrochemical cells involves attempts to reduce the overpotential and hence to increase the efficiency of electrolytic processes. 

In the membrane-cell process, highly selective ion-exchange membranes of Du Font s Nation type are used which allow only the sodium ions to pass. Thus, in the anode compartment an alkali solution of high purity is produced. The introduction of Nafion-type membranes in chlor-alkali electrolyzers led to a significant improvement in their efficiency. Today, most new chlor-alkafi installations use the membrane technology. Unfortunately, the cost of Nafion-type membranes is still very high. 

The productivity of modem electrolyzers per unit volume or unit of floor space as a rule is lower than that of chemical reactors with a similar purpose. This is due to the fact that in an electrochemical reactor the reactions occur only at the electrode surfaces, while in a chemical reactor they can occur in practically the full volume. Therefore, recent efforts go in a direction of designing new, more efficient electrochemical reactors. 

Depending on the size, type, and condition of an electrolysis plant, the energy requirement to produce 1 Nm3 of H2 lies in the range 4-6 kWh. With a hydrogen HHV of 3.5 kWh/Nm3, the efficiency of water electrolyzers lies in the range 58-87%. 

The development goals for water electrolyzers are oriented toward increasing the efficiency and reducing the cost. Most of the issues to be addressed are not specific to intermittent power operation. The efficiency of water electrolysis increases with the increasing... 

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