Enhanced Activity of Gold-Supported Cobalt Oxide for the Electrochemical Evolution of Oxygen

Abstract

Scanning electron microscopy, linear sweep voltammetry, chronoamperometry, and in situ surface-enhanced Raman spectroscopy were used to investigate the electrochemical oxygen evolution reaction (OER) occurring on cobalt oxide films deposited on Au and other metal substrates. All experiments were carried out in 0.1 M KOH. A remarkable finding is that the turnover frequency for the OER exhibited by ∼0.4 ML of cobalt oxide deposited on Au is 40 times higher than that of bulk cobalt oxide. The activity of small amounts of cobalt oxide deposited on Pt, Pd, Cu, and Co decreased monotonically in the order Au > Pt > Pd > Cu > Co, paralleling the decreasing electronegativity of the substrate metal. Another notable finding is that the OER turnover frequency for ∼0.4 ML of cobalt oxide deposited on Au is nearly three times higher than that for bulk Ir. Raman spectroscopy revealed that the as-deposited cobalt oxide is present as Co(3)O(4) but undergoes progressive oxidation to CoO(OH) with increasing anodic potential. The higher OER activity of cobalt oxide deposited on Au is attributed to an increase in fraction of the Co sites present as Co(IV) cations, a state of cobalt believed to be essential for OER to occur. A hypothesis for how Co(IV) cations contribute to OER is proposed and discussed.

Recent Progress in Energy‐Driven Water Splitting

“…Yeo et al examined this by depositing Co 3 O 4 on Au as well as other metallic substrates. It was found that the OER activity of Au‐supported Co 3 O 4 was 40 times higher than its bulk counterpart, whereas Co 3 O 4 with other metal substrates exhibited less significant enhancement 143. The OER activity of Co 3 O 4 increased with the increasing electronegativity of metal substrates in a sequence of Au > Pt > Pd > Cu > Co.…”

Redox and electrochemical water splitting catalytic properties of hydrated metal oxide modified electrodes

“…They found that the lowest OER onset potential was obtained for a manganese oxide modified Au substrate. In a number of recent publications, Bell and coworkers 25,27 have also highlighted the effect of the substrate on the electrocatalytic properties of Ni and Co oxides. In particular, they observed that the OER activity of a submonolayer of cobalt oxide decreases in the order CoO x /Au > CoO x /Pt > CoO x /Pd > CoO x / Cu > CoO x /Co.…”

“…In particular, they observed that the OER activity of a submonolayer of cobalt oxide decreases in the order CoO x /Au > CoO x /Pt > CoO x /Pd > CoO x / Cu > CoO x /Co. 27 This trend was interpreted in terms of the electronegativities of the substrates. That is, the more electronegative metals, such as Au, can facilitate the formation of higher Co oxidation states thereby improving the electrocatalytic properties of the oxide.…”

“…For instance hydroxylation reactions such as, (27) will result in the conversion of oxy to hydroxy species in the outer region of the surface layer. Also, place exchange processes can result in an increase in the thickness of the surface layer.…”

“…[13][14][15][16][17][18] Consequently, a significant body of research exists on the application of non-noble transition metal oxides as OER anodes. Among the most promising materials are various intermetallic alloys, [19][20][21] electrodeposited nickel, [22][23][24][25] cobalt [26][27][28] and manganese oxides, 29 spinels including nickelites, [30][31][32][33] cobaltites [34][35][36] and ferrites, 37,38 perovskites, [39][40][41][42] and hematite photoanodes. 43 An important practical and fundamental factor which should also be noted when considering OER anode materials is that, even in the case of the parent metal, the anodic OER always occurs at an oxidised surface.…”