DOI: 10.1002/celc.201402279 In Situ Tetraethoxysilane-Templated Porous Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3Àd Perovskite for the Oxygen Evolution Reaction Yisu Yang, Wei Zhou,* Ruochen Liu, Mengran Li, Thomas E. Rufford, and Zhonghua Zhu* [a] The perovskite Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3Àd (BSCF) is one of the best catalysts for the oxygen evolution reaction (OER), which is criti- cal to many energy-storage applications. However, the catalytic activity of BSCF perovskites is constrained by a low specific surface area (0.5 m 2 g À1 ). We report here, for the first time, a facile, in situ template method using tetraethoxysilane (TEOS) to synthesize porous BSCF with surface areas of up to 32.1 m 2 g À1 , which to our knowledge is the highest reported surface area in a BSCF perovskite, and with excellent catalytic activity for the OER. For example, the BCSF prepared using a TEOS-to-BSCF ratio of 3.4 exhibited up to 35.2 A g À1 at 1.63 V versus a reversible hydrogen electrode (overpotential, h = 0.4 V) and this current is 5.3 times that exhibited by nonporous BSCF (6.6 A g À1 ). The high activity of the porous BCSF is attrib- uted to the additional catalytic surface sites available in the pores created by the in situ TEOS-template method. The gen- eral application of this technique to produce porous perov- skites is demonstrated in the synthesis of a second example, porous LaMnO 3 . The generation of hydrogen by electrochemical water splitting is a potential route to store energy from intermittent renewa- ble energy sources, such as solar and wind. [1] However, the de- velopment of efficient and cost-effective water-splitting tech- nologies is limited by the kinetics of the oxygen evolution re- action (OER; 4OH À !O 2 + 2H 2 O + 4e À in alkali or 2H 2 O !O 2 + 4H + + 4e À in acid), which can be slow even when state-of-the- art precious metal catalysts such as iridium oxide (IrO 2 ) and ruthenium oxide (RuO 2 ) are applied. [1b] A potential alternative class of low-cost catalysts to the precious metal oxide catalysts is ABO 3 perovskites, which are composed of an alkali or a rare earth metal (A) with a transition metal or metals (B) and show promise as lower cost alternatives; [2] of these materials Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3Àd perovskite (BSCF) has been reported to have one of the highest intrinsic OER activities, due to an opti- mal e g orbital filling, which is close to unity. [2a] To realize the full advantage of the intrinsic OER activity of BSCF, it is desira- ble to maximize the surface area to mass ratio of the catalyst. We demonstrate here that the mass-normalized OER activity of BSCF can be enhanced fivefold by preparation of high specific surface area perovskites by using an in-situ silica sol–gel tem- plate method. The conventional approach used in catalysis to increase the specific surface area (SSA) of an active phase is to prepare nanoparticles, either supported on an inert structure, such as porous alumina, or in a colloidal suspension. Lee et al. [1b] re- ported such an approach for the preparation of rutile IrO 2 and rutile RuO 2 nanocatalysts. Recently, BaTiO 3 -type perovskite nanocrystals have been successfully synthesized at low tem- perature using the vapor diffusion sol–gel method by Brutchey et al. [3] However, the nanoparticle approach is less suitable for the preparation of perovskites, as the high temperatures (ap- proximately 900 8C for BSCF) required to calcine the perovskite can sinter the nanoparticles and result in low SSAs. Instead many researchers have investigated hard templating methods as a means to produce porous perovskites. [4] For example, Zhao et al. prepared three dimensional La x Sr 1Àx FeO 3Àd with poly(methylmethacrylate) (PMMA) microspheres, [5] Sadakane et al. prepared porous La x Sr 1Àx FeO 3Àd catalysts with colloidal polystyrene microspheres, [6] and Jiang et al. [7] and Lanfield et al. [4] each prepared strontium-based perovskites with cellu- lose-derived templates. A summary of porous perovskites pre- pared from templating methods is provided in Table S1 in the Supporting Information. One of the highest surface area perov- skites reported in the literature is a partly ordered mesoporous LaFe 0.4 Co 0.6 O 3 catalyst with a SSA of 163 m 2 g À1 ; this was syn- thesized by Wang et al. using the mesoporous silica KIT-6 as a template. [8] We attempted to follow the approach of Wang et al. to prepare BSCF perovskite by using a commercial meso- porous silica (Davisil Grade 643), but found the large grain size of the mesoporous silica hindered the formation of a crystalline BSCF phase (Figure S1). Furthermore, the multistage prepara- tion process for mesoporous silica templates is itself an expen- sive operation, and thus, a porous perovskite produced by this method is unlikely to be cost effective. In this study, our approach was the direct hydrolysis of tet- raethoxysilane (TEOS), as a template particle, concurrently and in situ with the BSCF precursor solution to form a homogenous sol. Scheme 1 illustrates the synthesis procedure and the ex- perimental details are provided in the Supporting Information. The TEOS + BSCF precursor gel was combusted at 260 8C then calcined at 900 8C, after which the solid was soaked in 2 m NaOH for 24 h to dissolve the silica impurities and leave a porous BSCF perovskite with a hierarchical pore structure. The effect of the silica on BSCF properties was investigated by [a] Y. Yang, Dr. W. Zhou, R. Liu, M. Li, Dr. T.E. Rufford, Prof. Z. Zhu School of Chemical Engineering, The University of Queensland St. Lucia, Queensland 4072 (Australia) Fax: (+)61 733654199 E-mail : wei.zhou@uq.edu.au z.zhu@uq.edu.au Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/celc.201402279.  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemElectroChem 0000, 00,1–4 &1& These are not the final page numbers! ÞÞ CHEMELECTROCHEM COMMUNICATIONS