Paper on Combined Exsolution and Electrodeposition Strategy for Enhancing Electrocatalytic Activity of Ti-Based Perovskite Oxides in Oxygen and Hydrogen Evolution Reactions

Abstract

The significant interest in perovskite oxides stems from their compositional and structural flexibility, particularly in the field of electrochemistry. In this study, the double E strategy (exsolution and electrodeposition strategies) is successfully devised for synthesizing perovskite-based bifunctional electrocatalysts, enabling simultaneous OER and HER applications with exceptional catalytic performance. The synthesized R-LCTFe/Ni catalyst exhibits outstanding electrocatalytic activity, delivering low overpotentials of 349 and 309 mV at 10 mA cm⁻² for OER and HER, respectively, indicating substantial improvements in the inherent electrocatalytic activity. Moreover, the impressive stability of R-LCTFe/Ni under alkaline conditions underscores its potential for practical water electrolysis applications. The superior bifunctional electrocatalytic performance can be attributed to the reduced charge transfer resistance and the synergistic cooperation between exsolved Fe nanoparticles and electrodeposited Ni compounds. The successful development of the R-LCTFe/Co catalyst further confirms the transferability of the double E strategy. Compared to R-LCTFe/Ni, the overpotential of R-LCTFe/Co is 58 mV higher for OER, yet 48 mV lower for HER at a current density of 10 mA cm⁻². This study provides an efficient and promising approach for the fabrication of highly active perovskite-based electrocatalysts, contributing valuable insights into the design of bifunctional electrocatalysts for OER and HER.

1 Introduction

As a strategy for addressing the challenges of energy scarcity and environmental degradation, it is crucial to prioritize the development of renewable and sustainable energy sources that can effectively replace fossil fuels in the future.^[1-3] Hydrogen has great potential as a zero-carbon energy carrier that is clean and renewable, because it does not cause pollution and it is widely available.^[4, 5] One of the most efficient and environmentally friendly ways to produce hydrogen is electrochemical water splitting, which can use renewable energy sources such as solar and wind to power the process.^[6-8] However, the intrinsically sluggish kinetics of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) remain a challenge in the electrochemical water splitting process.^[9-11] Consequently, considerable endeavors have been devoted to the development of highly efficient electrocatalysts capable of reducing energy barriers. While noble metals such as Ir/Ru oxides and Pt are widely recognized as state-of-the-art electrocatalysts for OER and HER, respectively, the high cost and limited availability severely constrain their large-scale applications.^[10-12] Therefore, it is crucial to design and synthesize electrocatalysts that are both economical and abundant. Perovskite oxides have emerged as a promising class of materials due to their cost-effectiveness, compositional flexibility, tunable electronic structures, and outstanding stability.^[13] Although titanium-based perovskites have been extensively utilized in solid oxide fuel cells (SOFCs), solid oxide electrolysis cells (SOECs), and photocatalysis, their potential as a bifunctional electrocatalyst for low-temperature water splitting remains largely untapped.^[14-20] This may be due to the inherently poor catalytic activity of titanium-based perovskites at room temperature. For example, Ikuya et al. systematically investigated 25 kinds of perovskite oxides for their OER catalytic performance, and found that the titanium-based perovskites could not even reach 0.05 mA cm⁻² at 1.8 V versus RHE.^[21] In recent years, our group has successfully enhanced the OER catalytic activity of titanium-based perovskites through the redox-exsolution method. For instance, in 2020, we improved the OER performance of CaTiO₃ by Ni exsolution,^[22] and last year, we systematically investigated the influence of Co doping levels and redox conditions on the OER catalytic activity of LCTCo.^[23] However, their intrinsic performance still falls short of the benchmark OER catalysts, RuO₂ and IrO₂.

Herein, to further enhance the catalytic activity of titanium-based perovskites, we propose a double E strategy, consisting of exsolution and electrodeposition in series, to greatly enhance the electrocatalytic activity of Ti-based perovskite oxide La_0.25Ca_0.65Ti_0.95Fe_0.05O₃ (LCTFe) for both OER and HER. Iron nanoparticles can be exsolved and anchored on the parent perovskite surface through reduction under a reducing atmosphere, generating a sample of R-LCTFe. This method can increase the number of active sites and improve the performance of the perovskite. Moreover, a significant enhancement in water splitting performance can be achieved by further depositing trace amounts of nickel onto the surface of R-LCTFe using a fast electrodeposition technique (R-LCTFe/Ni). The synergistic effect between the iron nanoparticles and the electrodeposited nickel not only enhances electron transfer efficiency but also creates a combined catalytic performance that exceeds the sum of their individual contributions, demonstrating a 1 + 1 > 2 effect. To validate the extensive applicability of the double E strategy, we further investigate the utilization of cobalt instead of nickel during the electrodeposition process. Under the conditions of a 10 mA cm⁻² current density, R-LCTFe/Co, in contrast to R-LCTFe/Ni, shows a 58 mV overpotential increase for OER and a 48 mV decrease for HER. In both R-LCTFe/Ni and R-LCTFe/Co, the content of active Fe and Ni (or Co) is quite small. Therefore, the double E strategy not only enhances the catalytic activity of Ti-based perovskites but also improves the atom utilization efficiency of the active elements, resulting in increased mass activity. Consequently, the double E strategy presents a promising approach for optimizing water splitting performance in Ti-based perovskite oxides doped with exsolvable metals. The broader implication is that this strategy can be extended to a wider range of material systems and electrocatalytic applications.

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Credit Authorship

Shangshang Zuo, Chenchen Wang, Zhi Xia, Jiaxin Ding, Aaron B. Naden, John T. S. Irvine

First published: 20 December 2024