Surface area of nanoporous gold: Effect on temperature

Abstract

Nanoporous Au in two distinctly different surface states, namely, positively charged as-dealloyed and reduced clean metallic were investigated for temperature dependent properties like specific capacitance Cs and specific mass surface area αm. An electrochemical double layer capacitance ratio method was employed to carry out these studies. It is shown that for reduced clean metallic nanoporous Au sample, the variation in ln (Cs) versus 1/T plot is almost linear, which supports to the negative temperature coefficient predicted by the double layer model. This observation is in direct contrast with positively charged as-dealloyed nanoporous Au that did not reveal any such trend. We compare the specific-mass surface area αm of nanoporous Au values with the geometrical surface area αg, obtained by using the “ball-stick geometrical model” coupled with scanning electron microscopy images. Evolution of ultra small nanometric structures during dealloying renders positively charged as-dealloyed nanoporous Au vulnerable to oxidation and ligament coarsening up on its reduction. The validation of the specific-mass surface area obtained from the capacitance ratio method was confirmed by Brunauer-Emmett-Teller analysis and the process of adsorption/desorption of OH adsorbed species on pore surfaces in reduced clean metallic np-Au.