Anodized Nickel Foam for Oxygen Evolution Reaction in Fe-Free and Unpurified Alkaline Electrolytes at High Current Densities

Abstract

To achieve practically high electrocatalytic performance for the oxygen evolution reaction (OER), the active surface area should be maximized without severely compromising electron and mass transport throughout the catalyst electrode. Though the importance of electron and mass transport has been studied using low surface area catalysts under low current densities (∼tens of mA/cm2), the transport properties of large surface area catalysts under high operating current densities (∼500 mA/cm2) for practical OER catalysis have rarely been explored. Herein, three-dimensional (3D) hierarchically porous anodized nickel foams (ANFs) with large and variable surface areas were synthesized via electrochemical anodization of 3D nickel foam and applied as OER electrocatalysts in Fe-free and unpurified KOH electrolytes. Using Fe-free and in situ Fe-doped ANF that were prepared in Fe-free and unpurified electrolytes, respectively, we investigated the interdependent effects of active surface area and transport properties on OER activity under practically high current densities. While activity increased linearly with active surface area for Fe-free ANF, the activity of Fe-doped ANF showed a nonlinear increase with active surface area due to lower electrocatalytic activity enhancement. Detailed investigations on the possible factors (Fe incorporation, mass transport, and electron transport) identified that electron transport limitations played the major role in restricting the activity enhancement with increasing active surface area for Fe-doped ANF, although Fe-doped ANF has electron transport properties better than those of Fe-free ANF. This study exemplifies the growing significance of electron transport properties in large surface area catalysts, especially those with superb intrinsic catalytic activity and high operating current density.

Co/MoC Nanoparticles Embedded in Carbon Nanoboxes as Robust Trifunctional Electrocatalysts for a Zn–Air Battery and Water Electrocatalysis

“…In order to understand the ORR reaction kinetics in depth, the corresponding Tafel slopes are plotted and displayed in Figure c. In general, a lower Tafel slope at a low overpotential region implies efficient kinetics in the catalytic process. ,− Interestingly, the Co@IC/MoC@PC sample also possesses the smallest Tafel slope of 78 mV/dec, thus suggesting its excellent kinetics. The charge-transfer resistance could be measured by the electrochemical impedance spectroscopy (EIS).…”

Dendrimer-Ni-Based Material: Toward an Efficient Ni–Fe Layered Double Hydroxide for Oxygen-Evolution Reaction

“…Smith’s group, using the density functional theory and near-infrared spectroscopy, indicated that the additive cations asymmetrically affect the voltage-induced expansion and contraction of the nickel hydroxide lattice . The peak at 1.39 V could be related to such Ni sites. − …”

Advances and Challenges in Industrial-Scale Water Oxidation on Layered Double Hydroxides

“…178 Alternatively, one can settle using Ni mesh as an anode that can be activated by anodization or used as a Ni source for the formation of OER active NiFeOOH. 169,179,180 Although pure Ni mesh is not highly active, its stability under operation conditions is remarkable. For example, the anode performance loss is less than 0.5% per year for commercial Ni mesh anodes with an expected lifetime of more than 5 years.…”

“…181 Controlling the reaction rate between oxidation and dissolution is needed to nanostructure the metal foams. 169,181 Fluoride-free approaches include cathodic deposition of nanostructured Ni deposit from the electrolyte containing Ni 2+ salts followed by anodic oxidation. 182 Recently, Wan et al 168 reported anodic oxidation of Ni foam in 1−10 M KOH at 1−3 A cm −2 for 3 h, where metal oxidation and oxygen evolution occur simultaneously to give a nanostructured electrode.…”