Zero charge potentials of platinum metals and electron work functions (Review)

The methods of determining the potentials of zero total charge (ZTCP) and zero free charge (ZFCP) of platinum metals are considered. Special attention is paid to the CO displacement technique developed in the recent 15 years. This method allows directly determining the so called zero displaced charge potentials (ZDCP) that for many systems are close to ZTCP. The published experimental data are tabulated by values of ZTCP/ZDCP for electrodes of smooth polycrystalline and dispersed (electrolytic deposits) metals; single crystal faces; stepped surfaces with different step density; adatom layers of platinum metals on well characterized ordered supports; single crystal faces decorated by foreign adatoms; nanoparticles with the given surface structure, controlled shape, or given size. The concepts of global and local zero charge potential values (ZCP) are analyzed. The effect of the composition and surface structure, solution composition and pH, electrode pretreatment conditions on the ZCP values is discussed. Special attention is paid to the results of determination of ZTCP and ZFCP of the most intriguing interface: Pt(111)/solution of electrolyte. The necessity is emphasized of detailed studies of the size dependence of ZCP as an important aspect of nanoelectrochemistry. In the cases when the corresponding data are accessible, the values of ZCP and electron work function are compared. It is assumed that such comparison in the case of platinum metals can refer both to ZTCP/ZDCP and ZFCP. The results of comparison are discussed with account for the contributions of solution ions, hydrogen atoms, and water molecules to potential drops at interfaces.