Bi/PO4/PSS(A)	Equal volumes of solutions of Na2HPO4 (4 mM), Bi(NO3)3 (1 mM), and PSS (25 mM) are mixed. Then, 5 μL of this solution is drop-casted onto the working electrode.
Bi/VO4/PSS(A)	Same as Bi/PO4/PSS(A), except using 3 mM NaVO2 instead of 4 mM Na2HPO4.
Bi/PO4/PSS(B)	2 μL of the 25 mM solution of PSS is drop-casted onto the working electrode and left drying. Then, 5 μL of a solution prepared by mixing equal volumes of Na2HPO4 (4 mM) and Bi(NO3)3 (1 mM) is drop-casted onto the working electrode.
Bi/VO4/PSS(B)	Same as Bi/PO4/PSS(B), except using 3 mM NaVO2 instead of 4 mM Na2HPO4.
Bi/PO4/PSS(B5)	2 μL of the 25 mM solution of PSS is drop-casted onto the working electrode and left to dry. Then, 5 μL of a solution prepared by mixing equal volumes of Na2HPO4 (20 mM) and Bi(NO3)3 (5 mM) is drop-casted onto the working electrode.
Bi/VO4/PSS(B5)	Same as Bi/PO4/PSS(B5), except using 15 mM NaVO2 instead of 20 mM Na2HPO4.
Bi/PO4/PSS(C)	5 μL of a solution prepared by mixing equal volumes of Na2HPO4 (4 mM) and Bi(NO3)3 (1 mM) is drop-casted onto the working electrode and left to dry. Then, 2 μL of the 25 mM solution of PSS is drop-casted onto the working electrode
Bi/VO4/PSS(C)	Same as Bi/PO4/PSS(C), except using 3 mM NaVO2 instead of 4 mM Na2HPO4.