Abstract
The electroless plating of palladium and palladium alloy membranes is fast becoming an important and enabling technology. This is more so when juxtaposed with the rising demand for high purity hydrogen for applications particularly in proton exchange membrane fuel cells (PEMFC). The effect of process factors such as sensitization and activation during surface modification, concentration of the reducing agent, plating temperature, time, pH, additives, air aeration on plating efficiency, quality of the palladium film and deposit morphology is reviewed with the aim of identifying areas requiring further investigation. The paper also reviews how these process factors could be optimised for better plating efficiency and overall membrane quality. The concentration of the reducing agent has been identified as the limiting factor on plating efficiency albeit other process factors separately impact on the plating efficiency. Furthermore, bulk precipitation caused by concentration of the reducing agent has been identified as a major problem during electroless plating with hydrazine based plating baths. To ameliorate this problem, a multi step addition of the hydrazine reducer in separate portions has been recommended.
Highlights
In palladium based membrane reactors, palladium membranes can be used in an equilibrium limited reaction to remove one of these products and increase the conversion or to selectively saturate hydrogen through the membrane in both scenarios, palladium has a catalytic function [4]
The common reducing agents used for the electroless plating of palladium and palladium alloy membranes are hydrazine, hydrophosphite, borohydride, dimethylamine boron and formaldehyde [21]
Palladium membranes suffer from hydrogen embrittlement and Pd/Ag membranes are resistant to hydrogen embrittlement due to their ability to avoid α – β phase transition [3]
Summary
Some of the several advantages the electroless plating method has over other methods include its uniformity and easiness of coating over any surface of any shape, no energy supplies required, low cost, simple equipment as shown in Figure 1 and it avoids accumulation of the deposits around the substrate edges to ensure in uniformity of coating [1] It has its drawbacks such as its time consuming procedure as a result of the several treatment steps involved [2]. Optimisation of these process factors is one critical way of ameliorating the mass transfer problem in the conventional electroless plating [8] [9]
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