Selectivity of Nanocrystalline IrO2-Based Catalysts in Parallel Chlorine and Oxygen Evolution

Abstract

This paper examines the detection and quantification of the potentially corrosive byproducts of the oxygen evolution reaction on iridium and iridium-ruthenium mixed oxides. A conventional but stationary ring-disc electrode was employed in a flow cell configuration for the detection of volatile reaction product other than oxygen, and the formation of at least two active species was detected.Potential-modulated UV-VIS reflectance spectroscopy helped to identify one of these volatile reaction byproducts as hydrogen peroxide, and the other is tentatively suggested to be ozone. It was found that these species are formed under potentiodynamic conditions due to the chemical recombination of the absorbed reaction intermediates. The influence of the electrode material composition on the production yield of these byproducts was studied, and we found that the generation of these corrosive reaction byproducts is suppressed the more active the catalyst is for the OER. The formation of by-products can therefore be addressed by a rational choice of the electrode materials based on the adsorption energy of the reaction intermediates as is done for the OER itself. Steady-state electrolysis minimizes hydrogen peroxide formation as byproduct of the oxygen evolution reaction.

Overpotential‐Dependent Volcano Plots to Assess Activity Trends in the Competing Chlorine and Oxygen Evolution Reactions

“…[4] Regrettably, the oxygen evolution reaction (OER) constitutes a detrimental anodic side reaction under CER conditions. [5][6][7][8] Even though conventionally applied dimensionally stable anodes (DSAs) [9][10][11] reveal CER selectivity of about 97-99 %, [12] the gaseous products Cl 2 and O 2 need to be separated from each other, corresponding to a significant fraction of the overall process costs. [13,14] Therefore, the development of an electrode material that is as stable as DSAs under the harsh anodic reaction conditions, but reveals higher CER selectivity than DSAs, is an ultimate dream of chemical industry.…”

Controlling Stability and Selectivity in the Competing Chlorine and Oxygen Evolution Reaction over Transition Metal Oxide Electrodes

“…[1][2][3][4] The anode material consists of Ti plates coated with TiO 2 À RuO 2 mixed oxides, commonly denoted as dimensionally stable anodes (DSA). [5][6][7] RuO 2 has been identified as active component of the DSA for electrochemical chlorine evolution (CER), [8] which is impaired by a selectivity problem: the evolution of gaseous oxygen (OER) is a competing side reaction in the same potential window of CER, [9][10][11][12][13] which from a thermodynamic point of view is even preferred over CER according to the smaller equilibrium potential.…”

Integrated Valorization of Desalination Brine through NaOH Recovery: Opportunities and Challenges

“…Chlorine evolution is thermodynamically less favorable than oxygen evolution, but because it is atwo-electron process rather than the four electrons required for OER, chlorine production is less kinetically hindered and thus can be more favorable than oxygen production. [57,[59][60][61] Oxygen-selective catalysts in acidic chlorinated conditions are relatively underexplored, yet afew promising early studies have reported selectivity for oxygen production from seawater by using doped manganese oxides. [58] Catalyst activities for OER and CER were initially found to follow the same trends,inwhich better OER catalysts were also better CER catalysts,b ut more recent studies have tuned the selectivity of OER over CER by adjusting the catalystse lectronic structure using dopants.…”

“…[57] Indeed, CER is typically favored over OER at acidic conditions. [62,63] More recent work used similar doped manganese oxides [52,64] and other doped oxides [59,61,65] to selectively produce oxygen even under acidic brine conditions with reasonable selectivity. [57,[59][60][61] Oxygen-selective catalysts in acidic chlorinated conditions are relatively underexplored, yet afew promising early studies have reported selectivity for oxygen production from seawater by using doped manganese oxides.…”

“…[58] Catalyst activities for OER and CER were initially found to follow the same trends,inwhich better OER catalysts were also better CER catalysts,b ut more recent studies have tuned the selectivity of OER over CER by adjusting the catalystse lectronic structure using dopants. [57,[59][60][61] Oxygen-selective catalysts in acidic chlorinated conditions are relatively underexplored, yet afew promising early studies have reported selectivity for oxygen production from seawater by using doped manganese oxides. [62,63] More recent work used similar doped manganese oxides [52,64] and other doped oxides [59,61,65] to selectively produce oxygen even under acidic brine conditions with reasonable selectivity.…”