Enhancement of Oxygen Evolution Activity of Nickel Oxyhydroxide by Electrolyte Alkali Cations

Abstract

Herein, the effect of the alkali cation (Li + ,Na + ,K + , and Cs + )inalkaline electrolytes with and without Fe impurities is investigated for enhancing the activity of nickel oxyhydroxide (NiOOH) for the oxygen evolution reaction (OER). Cyclic voltammograms showthat Fe impurities have asignificant catalytic effect on OER activity;h owever,b oth under purified and unpurified conditions,the trend in OER activity is Cs + > Na + > K + > Li + ,suggesting an intrinsic cation effect of the OER activity on Fe-free Ni oxyhydroxide.I nsitu surface enhanced Raman spectroscopy( SERS), shows this cation dependence is related to the formation of superoxo OER intermediate (NiOO À ). The electrochemically active surface area, evaluated by electrochemical impedance spectroscopy (EIS), is not influenced significantly by the cation. We postulate that the cations interact with the NiÀOO À species leading to the formation of NiOO À ÀM + species that is stabilized better by bigger cations (Cs + ). This species would then act as the precursor to O 2 evolution, explaining the higher activity.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Deciphering Iron‐Dependent Activity in Oxygen Evolution Catalyzed by Nickel–Iron Layered Double Hydroxide

“…Other factors previously proposed to explain the cation effect of OER, including enhanced water diffusion in the interlayer space and cation‐induced exfoliation can be ruled out because our LDH samples are ultrathin and have abundant accessible surface sites, and because our samples are not exfoliated in CsOH. We can also exclude a stabilizing interaction of NiOO − with Cs + because we did not observe an evolution of a shoulder peak between 930–950 cm −1 in CsOH (Supporting Information, Figures S12 and S13) . To probe the possibility of electric field effect due to Cs + adsorption, we measured OER in tetramethylammonium hydroxide (TMAOH) solution.…”

Importance of Water Structure and Catalyst–Electrolyte Interface on the Design of Water Splitting Catalysts

“…Furthermore, as previously discussed, the presence of cations can also affect the OER activity by self-insertion into the porous structure of NiOOH in addition to hydration enthalpy which modifies the energetics of the intermediates and the water structuring effect. 90 Future work is thus needed to fully understand and dissociate all these different effects. In light of the effect of ions observed on the performances of the most active OER catalysts, one must therefore consider more than just the binding energy of oxygen intermediates on the surface of the catalyst.…”

Electrolyte Engineering as a Key Strategy Towards a Sustainable Energy Scenario?

“…Notably, slightly before the contribution of Shinagawa, Obata, and Takanabe, Schuhmann and co‐workers demonstrated that by increasing the ionic strength of the electrolyte the selectivity ratio of the competing chlorine and oxygen evolution reactions significantly shifts towards the side of chlorine evolution, while Koper and co‐workers reported that the presence of alkali cations enhances the activity of Ni‐oxyhydroxides in the oxygen evolution reaction . Similarly, Bandarenka and co‐workers discussed the influence of alkali cations on the HER activity, demonstrating that activity trends correlate with the hydration energy of the corresponding alkali cations present in the electrolyte …”