Fast and Simple Preparation of Iron‐Based Thin Films as Highly Efficient Water‐Oxidation Catalysts in Neutral Aqueous Solution

Abstract

Water oxidation is the key step in natural and artificial photosynthesis for solar-energy conversion. As this process is thermodynamically unfavorable and is challenging from a kinetic point of view, the development of highly efficient catalysts with low energy cost is a subject of fundamental significance. Herein, we report on iron-based films as highly efficient water-oxidation catalysts. The films can be quickly deposited onto electrodes from Fe(II) ions in acetate buffer at pH 7.0 by simple cyclic voltammetry. The extremely low iron loading on the electrodes is critical for improved atom efficiency for catalysis. Our results showed that this film could catalyze water oxidation in neutral phosphate solution with a turnover frequency (TOF) of 756 h(-1) at an applied overpotential of 530 mV. The significance of this approach includes the use of earth-abundant iron, the fast and simple method for catalyst preparation, the low catalyst loading, and the large TOF for O2 evolution in neutral aqueous media.

Electro‐Oxidation of Ni42 Steel: A Highly Active Bifunctional Electrocatalyst

“…Therefore Tafel lines that can be assigned to both samples move (toward higher potentials) towards each other in the lower overpotential region (<500 mV) and move (toward higher potentials) apart from each other in the higher overpotential region (>500 mV) respectively (Figure 3b [31,89] were determined. We investigated oxidized standard carbon manganese steel S235 as a potential OER electrocatalyst in pH 7 regime and found at lower potentials a Tafel-slope of 172.4 mV dec -1 , which is comparable to the slopes reported here and those slopes reported in the literature [30,31,33] .…”

“…Generally the determined overpotentials for OER on recently developed materials in pH 7 media are relatively close to 500 mV at 1 mA cm -2 current density [30] . An overpotential of 610 mV for the onset of OER at pH 6.9 was reported for ZrS 3 nanosheets [31] .…”

“…An overpotential of 610 mV for the onset of OER at pH 6.9 was reported for ZrS 3 nanosheets [31] . Wu et al [30] reported a 480 mV overpotential at stable current density of 1 mA/cm films for OER in alkaline and neutral media and under optimal synthesis condition the films exhibited sufficient water splitting at pH 7 (470 mV overpotential at 1 mA/cm 2 current density) [32] .…”

Bi‐Functional Iron‐Only Electrodes for Efficient Water Splitting with Enhanced Stability through In Situ Electrochemical Regeneration

“…[ 30 ] Further, the scalability of phosphide materials is limited by toxicity and availability. Examples of iron oxyhydroxides operating as OER catalysts in alkaline solution are well known and operate in an overpotential range of 0.35-0.5 V, [38][39][40] but they have not been reported as HER catalysts. Chlorine oxidized stainless steels were also shown to be OER catalysts at alkaline (1.5 mA cm −2 at η = 260 mV) and neutral pH (1 mA cm −2 at η = 462 mV).…”

“…Hence iron is arguably the most attractive element on which to base sustainable catalysts, due to its effectively inexhaustible supply, low toxicity, and negligible environmental impact. Despite this, iron-based catalysts have been relatively underreported and underused, probably due to their notoriety for corrosion.Iron-based electrodes for either the HER or the OER have been reported, [35][36][37][38][39][40] but bi-functionally active iron-only materials in water splitting are unknown. For example, FeP is described as a promising high activity noble-metal-free material Scalable and robust electrocatalysts are required for the implementation of water splitting technologies as a globally applicable means of producing affordable renewable hydrogen.…”