The role of glycine in the iron-phosphorous alloy electrodeposition

The influence of glycine on the iron phosphorous alloy electrodeposition was investigated by electrochemical
quartz microbalance (EQMB), in-situ external reflection FTIR spectroscopy, and electrochemical
impedance spectroscopy (EIS) measurements. An increase of glycine concentration leads to a decrease of
the iron-phosphorous alloy electrodeposition rate and an increase of hydrogen evolution. Strong
adsorption of glycine species, such as H2(gly)þ, H(gly)± or/and Fe(gly)þ, have been observed during the
hydrogen evolution and the Fe-P deposition reaction. Due to the concurrent hydrogen evolution the pH
attains higher values at the interface than in the electrolyte bulk (pH2.5). The formation of adsorbed
Fe(gly)þ and of the chelate complex Fe(gly)2 in solution avoids the precipitation of Fe(OH)2 in the pH
range between 2.5 and ca. 7 at the interface. The phosphorous content of the iron phosphorous alloy
deposit increases with the glycine concentration. This is due to a lower deposition rate of iron caused by
the adsorption of Fe(gly)þ, while the hypophosphite reduction rate to phosphorous increases.