HC-PB preparation is based on a previously described method with modifications. An equimolar ratio of K 3 (Fe(CN) 6 and K 4 Fe(CN) 6 (10 mmol) was dissolved in a 150 mL 0.6 M HCl solution. The solution was heated to 80 o C and stirred for 20 hours. The resulting precipitate was filtered under vacuum and washed with DI water several times. The powder collected was dried in a vacuum oven at 80 o C for 3 hours.