They also can be organic or inorganic acids, such as HI and HCl [41], H3PO2 [42], HI + HBr [43], formic acid [44], trimesic acid [45], 2,2′-bipyridine (Bpy) and 2,2':6′,2″-terpyridine (Tpy) [46], and so on. Almost all of these chemical additives enhance PCE while ...