Electrocatalytic Oxygen Evolution Reaction in Acidic Environments – Reaction Mechanisms and Catalysts

Abstract

The low efficiency of the electrocatalytic oxidation of water to O2 (oxygen evolution reaction‐OER) is considered as one of the major roadblocks for the storage of electricity from renewable sources in form of molecular fuels like H2 or hydrocarbons. Especially in acidic environments, compatible with the powerful proton exchange membrane (PEM), an earth‐abundant OER catalyst that combines high activity and high stability is still unknown. Current PEM‐compatible OER catalysts still rely mostly on Ir and/or Ru as active components, which are both very scarce elements of the platinum group. Hence, the Ir and/or Ru amount in OER catalysts has to be strictly minimized. Unfortunately, the OER mechanism, which is the most powerful tool for OER catalyst optimization, still remains unclear. In this review, we first summarize the current state of our understanding of the OER mechanism on PEM‐compatible heterogeneous electrocatalysts, before we compare and contrast that to the OER mechanism on homogenous catalysts. Thereafter, an overview over monometallic OER catalysts is provided to obtain insights into structure‐function relations followed by a review of current material optimization concepts and support materials. Moreover, missing links required to complete the mechanistic picture as well as the most promising material optimization concepts are pointed out.

Using Instability of a Non-stoichiometric Mixed Oxide Oxygen Evolution Catalyst As a Tool to Improve Its Electrocatalytic Performance

“…Hence, the potential at the outer Helmholtz plane can be significantly lower. Interestingly, during the first 30 min of anodic polarization, about 18 ng cm −2 of Ir is dissolved from Ir 0.7 Sn 0.3 O 2-x , which is similar to that observed in the Ir-Ni system with 70 at% of Ir [10,34]. This can be an indication of similar kinetics of initial Ir dissolution for both materials.…”

“…2a). A similar trend was reported recently by Reier et al for the IrNi system [10,34]. This behavior can be understood by taking a closer look at the XPS data.…”

“…During both potential sweep and steady-state polarization regimes, the rate of Sn dissolution significantly exceeds the rate of Ir dissolution. A similar trend in dissolution was also observed in the case of Ir-Ru and Ir-Ni mixed oxides [10,14,34]. The onset of Ir dissolution is ca.…”

Electrocatalytic Metal–Organic Frameworks for Energy Applications

“…T herefore, the OERi sk inetically challenging, typically requires large overpotentials, and is considered one of the major roadblocksf or the storageo fr enewable energy in chemical fuels. [5,6,64,94,95] Precious-metal-basedc atalysts, such as RuO 2 and IrO 2 ,a re considered the benchmark for the OER;h owever,t heir high cost ands carcity limit their commercial viability. [94,95] The design of earth-abundant catalysts [a] BHT = benzenehexathiolate,T HT = triphenylene-2,3,6,7,10,11-hexathiolate,T HTA = mixed triphenylene-2,3,6,7,10,11-hexathiolate and triphenylene-2,3,6,7,10,11-hexamine.…”

Assessing the Potential of Co-Pt Bronze for Electrocatalysis in Acidic Media

“…While various nonprecious metals can be used as OER catalysts for alkali electrolysis [8], only precious metals can be used for acidic polymer electrolyte membrane electrolysis, which allows much higher current density compared to alkali electrolysis, and therefore, arguably lower overall cost for hydrogen production. Among the OER catalysts in acidic media, iridium and/or ruthenium (mixed) oxides are regarded as the most active [9][10][11]. For stabilities, ruthenium metal and oxides are regarded as unstable, since ruthenium forms volatile RuO4.…”