Synergistic multielement effect at the B-site of high entropy double perovskite oxide: A promising fuel electrode for efficient co-electrolysis of H2O and CO2

Abstract

The performance of the fuel electrode in a solid oxide electrolysis cell (SOEC) is crucial to facilitating fuel gas electrolysis and is the key determinant of overall electrolysis efficiency. Nevertheless, the commercialization of integrated CO2–H2O electrolysis in SOEC remains constrained by suboptimal catalytic efficiency and long-term stability limitations inherent to conventional fuel electrode architectures. A novel high-entropy Sr2FeTi0.2Cr0.2Mn0.2Mo0.2Co0.2O6−δ (SFTCMMC) was proposed as a prospective electrode material of co-electrolysis in this work. The physicochemical properties and electrochemical performance in the co-electrolysis reaction were investigated. Full cell is capable of electrolyzing H2O and CO2 effectively with an applied voltage. The effects of temperature, H2O and CO2 concentrations, and applied voltage on the electrochemical performance of Sc0.18Zr0.82O2−δ (SSZ)-electrolyte supported SOEC were investigated by varying the operating conditions. The SOEC obtains a favorable electrolysis current density of 1.47 A·cm−2 under co-electrolysis condition at 850°C with 1.5 V. Furthermore, the cell maintains stable performance for 150 h at 1.3 V, and throughout this period, no carbon deposition is detected. The promising findings suggest that the high-entropy SFTCMMC perovskite is a viable fuel electrode candidate for efficient H2O/CO2 co-electrolysis.

1. Introduction

The escalation of atmospheric CO2 concentrations, primarily resulting from fossil fuel combustion, has caused global warming and precipitated a cascade of environmental challenges [1–3]. Hence, developing integrated CO2 capture-conversion systems powered by renewable energy has emerged as a critical technological imperative. A solid oxide electrolysis cell (SOEC) is a high-temperature electrochemical reactor that efficiently stores intermittent renewable electricity as synthetic fuels through steam/CO2 co-electrolysis processes. Excess electrical/thermal energy drives the catalytic splitting of H2O into renewable H2 while reducing CO2 to syngas precursors [4–5]. The simultaneous electrolysis of H2O and CO2 produces tunable H2/CO syngas mixtures, presenting a prospective approach to energy storage applications for a fuel and the manufacture of synthetic fuels [6].

The co-electrolysis of H2O and CO2 offers a dual advantage in the setting of climate change mitigation and renewable energy integration. Specifically, it effectively reduces carbon emissions while also providing a mechanism to achieve effective storage of H2 and CO2, thereby facilitating progress toward carbon neutrality [7–8]. The electrolysis performance of co-electrolysis is more similar to steam electrolysis, with lower overpotentials and polarization resistance (Rp) compared to CO2 electrolysis, which exhibits slower reaction kinetics and requires higher activation energies [9]. The fuel electrode of SOEC may exhibit a high degree of susceptibility to reverse water–gas shift (RWGS) reactions when operated at high temperature, wherein electrochemically generated H2 reacts with CO2, yielding CO and H2O [10–11]. At high temperatures, where water electrolysis predominates, CO production is primarily driven by the RWGS reaction [12].

The co-electrolysis of H2O/CO2 primarily takes place at the fuel electrode. Currently, the fuel electrode in SOEC generally uses a similar structure and material system to the anode of solid oxide fuel cell (SOFC). The widely utilized fuel electrode material is Ni-yttrium stabilized zirconium oxide (Ni-YSZ) metal composite ceramics, which exhibit superior performance in high-temperature electrolysis [13–14]. However, a high concentration of H2 must be used as a protective gas to avoid oxidation of Ni [15–16]. This requirement not only raises the operating costs but also adds to complexity [17]. Moreover, they are susceptible to nickel coarsening and carbon deposition during long-term operation, which significantly reduces their activity and durability [18–19]. Therefore, the development of novel fuel electrode materials with superior co-electrolysis performance is imminently required. Perovskite oxides are gaining attention as potential alternatives to nickel-based ceramics, owing to their strong CO2 reduction reaction (CO2RR) capability and redox stability [20]. The main candidates include Sr2Fe1.5Mo0.5O6−δ (SFM) [21], La0.2Sr0.8TiO3−δ (LST) [22–23], La0.75Sr0.25Cr0.5Mn0.5O3−δ (LSCM) [24–25], etc. Although these perovskites show promise, the electrocatalytic activity and stability to carbon deposition remain insufficient and requires further enhancement. To develop fuel electrodes with superior electrochemical properties based on the synergistic multielement effect, this work proposes a novel high-entropy perovskite SFTCMMC.