The Aurivillius Compound CoBi₂O₂F₄ – an Efficient Catalyst for Electrolytic Water Oxidation after Liquid Exfoliation

Abstract

Investigation of new high‐efficiency catalysts for the oxygen evolution reaction (OER) is important for propelling the practical applications of water splitting. Here we report the Aurivillius compound CoBi2O2F4 to be a novel catalyst for catalytic OER. After liquid exfoliation of CoBi2O2F4 crystals in isopropanol, the resulting thin sheets deliver a low overpotential of 334 mV and a small Tafel slope of 47 mV dec−1 for catalytic OER, exhibiting substantially higher activity and faster kinetics compared with as‐synthesized crystals. This attributes to the increase in accessible surface area and dangling bonds on the edges providing more active sites exposed on the surface after exfoliation. The positive effects of F− anions to benefit OH− adsorption/combination and p‐block Bi3+ cations to direct reactants to preferred sites are proposed to synergistically improve the Co‐active centers for catalysis; based on this, the OER reaction mechanism on this new catalyst is discussed.

Recent Advances in Manifold Exfoliated Synthesis of Two‐Dimensional Non‐precious Metal‐Based Nanosheet Electrocatalysts for Water Splitting

“…Based on the research of 2D metal oxide‐based OER nanosheets catalysts, a 2D Co‐based oxofluoride nanosheet was prepared by a sonication treatment of bulk CoBi 2 O 2 F 4 in isopropanol for 6 h at room temperature. [ 14 ] The obtained 2D CoBi 2 O 2 F 4 nanosheets only need an overpotential of 0.334 V to reach 10 mA cm −2 current density in 1.0 m KOH for OER, outperforming commercial RuO 2 catalyst (0.353 V at 10 mA cm −2 ) (Figure 2c). Thanks to the numerous exposed active Co sites and the positive effects of F − anions and Bi 3+ cations, the reaction rate of OER process for 2D CoBi 2 O 2 F 4 nanosheets was obviously accelerated.…”

“…Reproduced with permission. [ 14 ] Copyright 2019, Wiley‐VCH. Pictures of d) bulk NiPS 3 powder and e) dispersion of 2D NiPS 3 nanosheets.…”

“…[ 5–9 ] However, precious metal‐based electrocatalysts are hard to be used in large scale of commercial applications, due to their high costs, poor stability, and low abundance in natural resources. Consequently, numerous low‐cost electrocatalysts based on earth‐abundant elements, such as metal oxides/hydroxides, [ 1,10–16 ] transition metal dichalcogenides (TMDs), [ 2,17–24 ] transition metal carbides and nitrides (TMNs and MXenes), [ 25–32 ] heteroatom‐doped carbons, [ 33–35 ] layered double hydroxides (LDHs), [ 36–38 ] metal–organic frameworks (MOFs), [ 39–42 ] monoelemental catalysts, [ 43–45 ] etc., have been developed to replace noble metal‐based electrocatalysts for water splitting. [ 3,46,47 ]…”

Symmetry and the Role of the Anion Sublattice in Aurivillius Oxyfluoride Bi2TiO4F2

“…The n = 1 Aurivillius oxyfluorides Bi 2 NbO 5 F and Bi 2 TaO 5 F, 37 Bi 2 VO 5 F, 38 Bi 2 TiO 4 F 2 , 39 and Bi 2 CoO 2 F 4 40 are less well understood but are increasingly attracting attention for their photocatalytic behavior, 41 − 44 and this is thought to be influenced by their polar and dielectric properties. 45 However, the dielectric behavior of Bi 2 TiO 4 F 2 is still not fully understood: it was first considered as a ferroelectric 46 , 47 with a ferroelectric Curie temperature T C = 284 K, 47 but later, experimental work on bulk ceramic samples found no evidence of ferroelectricity or of a polar crystal structure.…”

Engendering Unprecedented Activation of Oxygen Evolution via Rational Pinning of Ni Oxidation State in Prototypical Perovskite: Close Juxtaposition of Synthetic Approach and Theoretical Conception

“…[41][42][43] Ideally, in exfoliation, both approaches can be explored simultaneously. [44][45][46][47] It may be summarized that the optimization effects employed in the case of LaNiO3 are based on exploring minor adjustments to the structure of the catalyst and/or on the maximization of the materials specific area without aspiring to improve the intrinsic activity of the catalyst on an atomary level.…”