Nickel and Commercially Available Nickel‐Containing Alloys as Electrodes for the Electrochemical Oxygen Evolution

Abstract Water electrolysis is a crucial technology for independency on fossil fuels. However, water splitting is limited by the sluggish kinetics of oxygen evolution reaction (OER). While many studies report highly active, non‐precious metal‐based electrocatalysts for alkaline OER, applicability under industrial conditions is often omitted. Such conditions require catalysts being applied on nickel or nickel‐containing alloys in elevated electrolyte concentrations. In contrast to the rather inert substrates often used in scientific studies, such industrially applied substrates exhibit significant OER activity themselves and show dynamic behaviour. Therefore, it is crucial to understand the OER behaviour of such substrates. Here, nickel and seven commercially available nickel‐containing alloys are investigated as anodes in alkaline OER and their elemental compositions correlated to their corresponding activities. Repeated potential cycling across the Ni(II)/Ni(III)‐redox couple is established as activity‐enhancing procedure. Overall, the nickel‐base alloy Hastelloy® X exhibits the highest activity due to its Fe‐, Cr‐, Mo‐ and Co‐content. Though, the activity gain differs significantly for the various materials. Comparing Ni and Hastelloy® X as least and most active materials, the positive impact of activation on both activity and stability becomes evident. While untreated Ni suffers from poor OER stability, the activity‐enhancing procedure also significantly increases electrode stability in 24 h chronopotentiometry

Elucidating the Influence of Intercalated Anions in NiFe LDH on the Electrocatalytic Behavior of OER: A Kinetic Study

Abstract The oxygen evolution reaction (OER) as one half‐cell reaction of electrochemical water splitting has a fundamental impact on water splitting efficiency and thus on the competitiveness of electrochemically generated hydrogen in the energy market. Nickel‐iron layered double hydroxides (NiFe LDH) are among the most promising electrocatalysts for efficient OER under alkaline conditions. Despite intensive research, correlations of the material properties and the resulting kinetically limiting surface processes are poorly investigated. This work focuses on the kinetic behavior of NiFe LDH catalysts containing different anions in the basal spacing in alkaline OER. Steady‐state Tafel plots, impedance measurements as well as reaction order plots were used to elucidate differences in the catalytic performance. All catalysts showed a dual Tafel behavior and fractional reaction orders. For kinetic modelling, the physisorbed hydrogen peroxide mechanism and Temkin adsorption model were adopted to fit experimental data. Our study showed that the intercalated anions affect the kinetics of rate determining steps. The hypophosphite intercalated LDH possessed the highest OER activity and the first step as rate determining. While for both carbonate and borate intercalated NiFe LDH, the second step proved to be rate determining in the low Tafel region, while the first step was found to be rate‐limiting in the high Tafel region