Smart Control of Composition for Double Perovskite Electrocatalysts toward Enhanced Oxygen Evolution Reaction

Abstract

Double perovskites have emerged as efficient candidates for catalyzing the electrochemical oxygen evolution reaction (OER). Smart control of the composition of a B‐site ordered double perovskite can lead to improved catalytic performance. By adopting a facile co‐doping strategy, the OER‐active elements are simultaneously introduced into the B‐site and B′‐site of a B‐site‐ordered double perovskite (A2BB′O6), leading to an enhancement of the exposed reactive sites and an optimum surface chemical state. As a result, a model system built from the substitution of Co for Mo and Fe in the Sr2FeMoO6−δ double perovskite (with a composition of Sr2Fe0.8Co0.2Mo0.6Co0.4O6−δ) shows significantly enhanced OER activity in alkaline media compared with the host material, requiring an overpotential of 345 mV to reach a 10 mA cm−2 current density (catalyst loading≈0.232 mgcat cm−2GEO) and a cell voltage of 1.57 V to afford the same current density for the overall water splitting when coupled with a Pt/C cathode (catalyst loading≈2 mg cm−2). It also demonstrates excellent electrochemical stability. The generalizability of the compositional control methodology has also been demonstrated in double perovskites incorporating transition metals other than Co (e.g., Ni).

Bulk and Surface Properties Regulation of Single/Double Perovskites to Realize Enhanced Oxygen Evolution Reactivity

“…All the powders were synthesized by a facile sol‐gel method, involving thermal‐induced self‐assembly at high temperature . The as‐synthesized material structure was initially investigated using laboratory‐based XRD (Figure S1), which revealed a hybrid DP and SP oxide composition as shown by the reflection of at ≈19.5° arising from B‐site ordering .…”

“…The single/double perovskite (SP/DP) system with the nominal composition Sr 2 Fe 0.2 Co 0.8 Mo 0.65 Ni 0.35 O 6−δ , double perovskite Sr 2 Fe 0.8 Co 0.2 Mo 0.65 Ni 0.35 O 6−δ , and single perovskite SrFe 0.5 Co 0.5 O 3−δ were synthesized by a sol‐gel method . Taking Sr 2 Fe 0.2 Co 0.8 Mo 0.65 Ni 0.35 O 6−δ (10 mmol) as an example, Sr(NO 3 ) 2 (4.2326 g), Fe(NO 3 ) 3 ⋅9 H 2 O (3.2320 g), Co(NO 3 ) 2 ⋅6 H 2 O (1.7462 g), (NH 4 )Mo 7 O 24 ⋅4 H 2 O (1.1476 g), and Ni(NO 3 ) 2 ⋅6 H 2 O (1.4540 g) (all analytical grade from Sinopharm Chemical Reagent Co., Ltd.) were dissolved in deionized water with the assistance of citric acid (CA, 16.8 g) and C 10 H 16 N 2 O 8 (EDTA, 11.6 g).…”

“…Xu and co‐workers reported that the partial substitution of Fe in CoAl 2 O 4 allowed the control of surface reconstruction to form active oxyhydroxides under OER conditions, improving catalytic performance . Additionally, high‐valence 3 d‐transition metal ions incorporated into metal oxides are known to achieve a high reactivity towards water oxidation, which have been confirmed by some highly covalent oxides with lattice oxygen involved …”

“…Among many candidate materials, single perovskites of ABO 3 ‐type where A and B are commonly rare‐earth and transition‐metal elements, respectively, are regarded as promising OER electrocatalysts owing to low cost, rich composition, flexible crystal structure, and tunable lattice and surface defects . The OER activity of such perovskites can be boosted through tailoring the crystal, defect, or electronic structure.…”

Designing High‐Valence Metal Sites for Electrochemical Water Splitting

“…[ 9a,28b ] In addition, Co ions have rich and tunable redox behaviors, including valence states (Co 2+ , Co 3+ , and Co 4+ ) and spin states (low spin, intermediate spin, and high spin) that provide wide opportunities to design and construct desired properties. [ 127 ] A number of excellent reviews of Co‐based electrocatalysts are available. [ 10a,b,28b ] In this section, we briefly emphasize the application of high‐valence Co sites in designing excellent electrocatalysts for water splitting ( Table 2 ).…”