Effects of Gold Substrates on the Intrinsic and Extrinsic Activity of High-Loading Nickel-Based Oxyhydroxide Oxygen Evolution Catalysts

Abstract

We systematically investigate the effects of Au substrates on the oxygen evolution activities of cathodically electrodeposited nickel oxyhydroxide (NiOOH), nickel-iron oxyhydroxide (NiFeOOH), and nickel-cerium oxyhydroxide (NiCeOOH) at varying loadings from 0 -2000 nmol of metal/cm 2 . We determine that the geometric current densities, especially at higher loadings, were greatly enhanced on Au substrates: NiCeOOH/Au reached 10 mA/cm 2 at 259 mV overpotential, and NiFeOOH/Au achieved 140 mA/cm 2 at 300 mV overpotential, which were much greater than those of the analogous catalysts on graphitic carbon (GC) substrates. By performing a loading quantification using both inductively coupled plasma optical emission spectrometry and integration of the Ni 2+/3+ redox peak, we show that the enhanced activity is predominantly caused by the stronger physical adhesion of catalysts on Au. Further characterizations using impedance spectroscopy and in situ X-ray absorption spectroscopy revealed that the catalysts on Au exhibited lower film resistances and higher number of electrochemically active metal sites. We attribute this enhanced activity to a more homogeneous electrodeposition on Au, yielding catalyst films with very high geometric current densities on flat 3 substrates. By investigating the mass and site specific activities as a function of loading, we bridge the practical geometric activity to the fundamental intrinsic activity.

Effects of Metal Electrode Support on the Catalytic Activity of Fe(oxy)hydroxide for the Oxygen Evolution Reaction in Alkaline Media

“…The lack of activity increase in metal‐ion‐contaminated electrolyte may imply weak adhesion/adsorption of metal oxide (MO x ) species to the glassy carbon surface. This poor adhesion has been demonstrated previously to affect charge transfer in catalysts intentionally deposited onto glassy carbon as an electrode substrate . Au is the most affected by solution impurities, with the OER current increasing by roughly an order of magnitude as the electrolyte purity decreases.…”

“…This improved charge transfer at the Au / transitionmetal-oxide interface may be due to an increased strength of adsorption or adhesion of the oxide to the Au surface, which has been reported before for NiFeO x H y on Au. [20] This increased adhesion strength is tentatively supported by XPS analysis after performing electrochemistry in KOH with 1 ppm Fe (Figure 4). Despite the fact that electrochemical analysis indicates OER activity from FeO x species, after removing the electrodes from solution and rinsing with H 2 O, Fe is only observed on Au and Cu substrates, not Pt or Pd (Figure 4).…”

“…The electron‐withdrawing ability of the substrate is dependent on the substrate's electronegativity, but also on the ability to transfer charge at the interface between substrate and catalyst. Studies comparing NiO x H y and Ni(Fe)O x H y on GC and Au substrates have indicated that the nominal Ni 2+/3+ oxidation is “more complete” on Au than GC substrates, apparently indicating poorer charge transfer at the interface for the GC substrate. This improved charge transfer at the Au / transition‐metal‐oxide interface may be due to an increased strength of adsorption or adhesion of the oxide to the Au surface, which has been reported before for NiFeO x H y on Au .…”

“…Studies comparing NiO x H y and Ni(Fe)O x H y on GC and Au substrates have indicated that the nominal Ni 2+/3+ oxidation is “more complete” on Au than GC substrates, apparently indicating poorer charge transfer at the interface for the GC substrate. This improved charge transfer at the Au / transition‐metal‐oxide interface may be due to an increased strength of adsorption or adhesion of the oxide to the Au surface, which has been reported before for NiFeO x H y on Au . This increased adhesion strength is tentatively supported by XPS analysis after performing electrochemistry in KOH with 1 ppm Fe (Figure ).…”

“…The enhancement of the OER activity of other transition metal (oxy)hydroxides (Mn, Co, Ni, NiFe) by Au and other noble metals (Pt, Ag, Cu, Pd) has also been investigated . Yeo and Bell showed enhanced OER activity of Au‐supported Ni and Co oxides, which they attributed to charge transfer from the transition metal to the electronegative Au substrate .…”