Solution-Cast Metal Oxide Thin Film Electrocatalysts for Oxygen Evolution

Abstract

Water oxidation is a critical step in water splitting to make hydrogen fuel. We report the solution synthesis, structural/compositional characterization, and oxygen evolution reaction (OER) electrocatalytic properties of ~2-3 nm thick films of NiO(x), CoO(x), Ni(y)Co(1-y)O(x), Ni(0.9)Fe(0.1)O(x), IrO(x), MnO(x), and FeO(x). The thin-film geometry enables the use of quartz crystal microgravimetry, voltammetry, and steady-state Tafel measurements to study the electrocatalytic activity and electrochemical properties of the oxides. Ni(0.9)Fe(0.1)O(x) was found to be the most active water oxidation catalyst in basic media, passing 10 mA cm(-2) at an overpotential of 336 mV with a Tafel slope of 30 mV dec(-1) with oxygen evolution reaction (OER) activity roughly an order of magnitude higher than IrO(x) control films and similar to the best known OER catalysts in basic media. The high activity is attributed to the in situ formation of layered Ni(0.9)Fe(0.1)OOH oxyhydroxide species with nearly every Ni atom electrochemically active. In contrast to previous reports that showed synergy between Co and Ni oxides for OER catalysis, Ni(y)Co(1-y)O(x) thin films showed decreasing activity relative to the pure NiO(x) films with increasing Co content. This finding is explained by the suppressed in situ formation of the active layered oxyhydroxide with increasing Co. The high OER activity and simple synthesis make these Ni-based catalyst thin films useful for incorporating with semiconductor photoelectrodes for direct solar-driven water splitting or in high-surface-area electrodes for water electrolysis.

Efficient Water Splitting Cascade Photoanodes with Ligand‐Engineered MnO Cocatalysts

“…Therefore, most of the previously reported results related to BiVO 4 ‐based photoanodes13, 14, 16, 19, 47, 51, 52, 53 were measured in sulfite oxidation condition to show photo‐electrochemical properties of BiVO 4 ‐based electrodes independently of its poor water oxidation kinetics, as shown in Table S2 (Supporting Information). The photo‐electrochemical current densities of the BiVO 4 ‐based photoanodes4, 13, 14, 16, 17, 19, 20, 21, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 64, 65, 66, 67, 68, 69, 77 were plotted as a function of potential versus RHE. Thus, we measured PEC properties of BiVO 4 ‐based anodes under sulfite oxidation to figure out the effect of ligand engineering.…”

“…Specifically, under neutral condition, manganese oxide nanoparticles exhibited superior performance to previously reported transition metal–based catalysts 32, 33. Several researches show that Mn‐based oxides have superior catalytic activity at neutral pH and are highly active in water oxidation compared to low activity oxides, as shown in Table S1 (Supporting Information) 31, 32, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49. As compared to other OECs, Mn‐based oxides showed good catalytic properties (Tafel slope and overpotential) in the neutral pH condition for water oxidation.…”

Improving O2 production of WO3 photoanodes with IrO2 in acidic aqueous electrolyte

“…37 For electrodeposited catalyst electrodes, a literature method was used to electrodeposit IrO 2 . 38 An aqueous electrodeposition bath of 20 mM oxalic acid and 4 mM K 3 IrCl 6 was adjusted to pH 10 with Na 2 CO 3 and aged for >10 days.…”

Chemical Recognition of Active Oxygen Species on the Surface of Oxygen Evolution Reaction Electrocatalysts

“…A recent report by the Boettcher group demonstrated that iron contamination is at the origin of its large OER activity 19. Subsequent studies have shown that iron serves multiple purposes for Ni(Fe)OOH catalysts:20 1) it adopts a different local environment with unusually short Fe−O bond distance as shown by operando X‐ray absorption spectroscopy (XAS);21 2) it modifies the redox activity of nickel;17 and 3) it improves the electronic conductivity of the film 22.…”