Adsorption of 2-amino-5-nitropyridine on the (111) and (210) silver faces

The adsorption isotherms of 2-amino-5-nitropyridine (ANP) on the (111) and (210) silver faces from an aqueous solution of 0.09 M KClO4 + 0.02 M NaOH were determined at -0.4 V vs. the 1 mol-1 calomel electrode using double-potential-step chronocoulometry. The surface concentration ΓANP of ANP was obtained by stepping the applied potential from -0.4 V, where ANP is electroinactive, to -1.2 V, where ANP is electroreduced to 2,5-diaminopyridine. The charge involved in this step, once corrected for the diffusive and capacitive contributions, yields 6FΓANP directly. The maximum surface concentration and standard Gibbs energy of adsorption are equal to 3.6 × 10-10 mol cm-2 and -35 kJ mol-1 on Ag(111) and 5.2 × 10-10 mol cm-2 and 42 kJ mol-1 on Ag(210), thus demonstrating the strong effect of surface crystallography on the energetics of ANP adsorption.