Potentiodynamic behaviour of the rhodium/H2SO4(aq) interface in the potential range of the hydrogen and oxygen electrosorption

Abstract

The electrochemical response of Rh/H3SO4(aq) interfaces at 25°C, subjected to different potential-time perturbation programs in the potential range of H and 0 electrosorption and H and 0 electrodesorption is reported . The H electrosorption and H electrodesorption involve the participation of at least two distinguishable adsorption states. The degree of reversibility of the corresponding electrochemical processes is appreciably influenced by the history of the electrode including the type of perturbation applied to the electrode in the 0 electrosorption potential range.The 0 electrosorption and 0 electrodesorption involve the formation of different surface species as it is deduced either from the charge balance or from the kinetic response of the electrochemical interface . The early stages of the anodic reaction are interpreted through a reversible charge transfer comprising the formation of OH adsorbed species which later undergoes electrochemical and chemical reactions yielding different 0-containing species . The existence of the various 0-containing surface species as well as the influence of the most stable ones in the H electrosorption potential range is evidenced through their potentiodynamic electrodesorption . The kinetic results of the 0 electrosorption are discussed in terms of aging mechanisms including anion adsorption .

Hydrogen/anion electrosorption at rhodized electrodes as revealed by electrochemical impedance spectroscopy

“…1 and 2 as three potential values (denoted by arrows) characteristic for the hydrogen adsorption/desorption pair, ''doublelayer'' region and reversible part of the oxy(hydroxide) film formation [1][2][3][4][9][10][11]15]. At three different potential values, different shapes of impedance spectra are obtained with either different u plots, or different numbers of characteristic break frequencies or ''bends'', denoting positions of changing slopes in log jZ el j [31].…”

“…The upper potential limit was chosen to avoid the potential region of the surface (oxy)hydroxide formation/reduction [1,10] and loss of the rhodium material at high anodic potential values [1,21]. (ii) When immersed in test electrolyte solution (H 2 SO 4 or HClO 4 ), previously conditioned rhodium electrode was held for about 1 h to attain the equilibrium at the open circuit potential and then the electrode was polarised to this potential value.…”

“…Utility of application of the electrochemical impedance spectroscopy (EIS) for the rhodium electrode in this potential region can be easily predicted from the literature concerned on voltammetry [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], radiochemical coverage experiments [9,[17][18][19][20], electrochemical quartz crystal microbalance technique [20,21], and surface spectroscopy [8,16,[22][23][24][25] of various kinds of rhodium (smooth polycrystalline, single-crystal, ad-layer, and rhodized) electrodes. Almost all of these studies commonly suggested the presence of different adsorption phenomena in this region of polarisation potentials, including under-potential deposition (UPD) of hydrogen at potentials positive to the reversible H þ /H 2 potential, adsorption of various (an)ions present in electrolyte solutions, and adsorption of oxygen containing species prior to formation of the bulk oxides.…”

Temperature Dependence of Growth of Surface Oxide Films on Rhodium Electrodes

“…In the case of electroformation of oxides, the extend of surface oxidation depends on the nature of the metals, the polarization conditions (polarization potential, current density or time, E p , i p and t p , respectively) and the electrolyte composition and pH (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). The oxide formed on an electrode surface markedly affects anodic Faradaic electrode processes at the double-layer by: (i) afFecting the reaction energetics; (ii) changing electronic properties of the metal electrode; (iii) imposing a barrier to the charge transfer; (iv) affecting the adsorption properties of the reaction intermediates and products (14)(15)(16)(17).…”

“…At noble metals, the growth of submonolayer and monolayer oxides can be studied in detail by application of electrochemical techniques such as cyclicvoltammetry, CV (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and such measurements allow precise determination of the oxide reduction charge densities. Complementary X-Ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), infra-red (IR) or ellipsommetry experiments lead to elucidation of the oxidation state of the metal cation within the oxide and estimation of the thickness of one oxide monolayer (12,(21)(22)(23).…”