Preparation of hydrogen peroxide by cathodic reduction of oxygen in porous electrodes made of different carbonaceous materials

Abstract

The rate of formation of hydrogen peroxide by cathodic reduction of oxygen in porous electrodes made of natural graphite, electrographite, carbon black and active carbon has been studied, as well as the catalytic effect of these materials on spontaneous decomposition of alkaline solutions of hydrogen peroxide. The measured data revealed that the greatest current yields of hydrogen peroxide were attained with electrodes made of low-surface kinds of carbon black which simultaneously had the lowest catalytic effect on the spontaneous decomposition of hydrogen peroxide.Cathodic reduction of oxygen can proceed, according to the character of electrode material and the reaction conditions, either in two consecutive two-electron steps which can be, e.g. for alkaline medium, expressed by equations 02 + H 2 0 + 2 e --;.. HO l + OH-; Ef98 = -0,076 V,HO l + H 2 0 + 2 e --;.. 3 OH -; Ef98 = + 0'878 V, (B) or as a direct four-electron reaction, described by the overall equation 02 + 2 H 2 0 + 4 e --;.. 40H-; Ef98 = + 0'401 V. (C)Two-electron reduction of oxygen according to reaction (A) proceeding under the formation of hydrogen peroxide as a relatively stable intermediate, takes place e.g. on mercury and on some carbonaceous materials 1 , 2. Direct four-electron reduction according to overall Eq. (C) is known to proceed, at least in part, on electrodes made of noble metals (Pt, Au, Rh)3 -6. The primarily . formed hydrogen peroxide, or the perhydroxyl anion, however, is not a thermodynamically stable product and therefore it can spontaneously decompose to form again gaseous oxygen and water or hydroxyl ions according to the overall equation (again written for alkaline medium) 2 HOi' --;.. 20H-+ °2 ; Ll.Cf98 = -184'09 kJ . (D) This, from the point of view of hydrogen peroxide preparation, unwanted decomposition reaction is considerably catalyzed by various both homogeneous and heterogeneous catalysts, present in the reaction system.

Electrochemical synthesis of hydrogen peroxide with a three‐dimensional rotating cylinder electrode

“…Thus, 0.5 mol L ‐1 NaOH is an attractive supporting electrolyte due to the resulting high values of limiting current densities and an acceptable conductivity. Limiting currents are well defined at NaOH concentrations higher than 2 mol L ‐1 , but at lower concentrations the first wave presents a peak, which was also previously reported . The decay in the current density at more negative potentials of the porous electrodes was attributed to flooding of the carbon pores because the hydrogen peroxide oxidizes its surface thus becoming more hydrophilic .…”

“…Limiting currents are well defined at NaOH concentrations higher than 2 mol L ‐1 , but at lower concentrations the first wave presents a peak, which was also previously reported . The decay in the current density at more negative potentials of the porous electrodes was attributed to flooding of the carbon pores because the hydrogen peroxide oxidizes its surface thus becoming more hydrophilic . Taylor and Humffray proposed that the unexpected minimum of current for an activated electron transfer process is due to a decrease in the number of electrocatalytic active surface sites for oxygen reduction.…”

“…Therefore, a controlled flow trickle bed reactor was developed using a porous cathode composed of a bed of graphite chips coated with PTFE and carbon black . A second strategy for the cathodic manufacture of hydrogen peroxide is the use of oxygen gas‐diffusion electrodes . High hydrogen peroxide concentration with low specific energy consumption was reported in concentrated alkaline solutions .…”

Simulation of the Polarization Curves for Oxygen Reduction at a Rotating Disk Electrode

“…completes the set of equations needed to solve for the c~ and (P unknowns. The boundary conditions in the bulk solution and at the electrode surface are, respectively, at = 2 c~ = c~.~ and ~I ) : (:])re [7] and m s~,j ij -Ni ~=0 = '= ~ + si'4rs [8] where r~ is the catalytic rate of decomposition of peroxide at the electrode surface and m is the number of charge-transfer reactions occurring at the electrode surface, s~.j is the stoichiometric coefficient of species i, and nj the number of electrons transferred in reaction j, when written in the form E s~jM~ ~ ---> nf- [9] i Kinetic equations.--The kinetic rate equations for the electrochemical reactions at the electrode surface are approximated by the Butler-Volmer expression for the current density…”

“…The 2e-reduction of oxygen by Eq. [2], proceeding with the formation of peroxide as a stable intermediate, occurs on mercury and some carbon electrodes (8,9). With nondoped low ash carbons, and in the absence of any other catalysts, peroxide concentrations as high as 1M are attainable (10).…”