Corrosion and protection of metallic materials in molten carbonates for concentrating solar power and molten carbonate electrolysis applications

Molten carbonates have recently attracted increasing interest for use as effective functional media in the fields of sustainable energy processes such as the Concentrating Solar Power (CSP) plants and the molten carbonate electrolysis (MCE) process. The compatibility between metallic materials and molten carbonate media is one of the important considerations and significant technical challenges for the practical molten carbonate application. Herein, we summarized the behaviors and mechanisms of molten carbonate-induced corrosion of metallic materials. The effects of operating temperature, gas atmosphere, electrochemical polarization, alloy elements, gas-liquid interface, and dynamic conditions on the corrosion behaviors and mechanisms of metals in molten carbonates were systematically reviewed. In addition, the corrosion mitigation approaches including regulation of melt basicity and surface treatments of metals are discussed. This review will serve as the foundation for further research addressing the challenges of molten carbonate-induced corrosion and enabling the effective applications of molten carbonates in a sustainable and low-carbon world

A general descriptor for guiding the electrolysis of CO2 in molten carbonate

Molten carbonate is an excellent electrolyte for the electrochemical reduction of CO2 to carbonaceous materials. However, the electrolyte–electrode-reaction relationship has not been well understood. Herein, we propose a general descriptor, the CO2 activity, to reveal the electrolyte–electrode-reaction relationship by thermodynamic calculations and experimental studies. Experimental studies agree well with theoretical predictions that both cations (Li+, Ca2+, Sr2+ and Ba2+) and anions (BO2−, Ti5O148−, SiO32−) can modulate the CO2 activity to control both cathode and anode reactions in a typical molten carbonate electrolyzer in terms of tuning reaction products and overpotentials. In this regard, the reduction of CO32− can be interpreted as the direct reduction of CO2 generated from the dissociated CO32−, and the CO2 activity can be used as a general descriptor to predict the electrode reaction in molten carbonate. Overall, the CO2 activity descriptor unlocks the electrolyte–electrode-reaction relationship, thereby providing fundamental insights into guiding molten carbonate CO2 electrolysis

A durable and pH-universal self-standing MoC-Mo2C heterojunction electrode for efficient hydrogen evolution reaction.

Efficient water electrolyzers are constrained by the lack of low-cost and earth-abundant hydrogen evolution reaction (HER) catalysts that can operate at industry-level conditions and be prepared with a facile process. Here we report a self-standing MoC-Mo2C catalytic electrode prepared via a one-step electro-carbiding approach using CO2 as the feedstock. The outstanding HER performances of the MoC-Mo2C electrode with low overpotentials at 500 mA cm-2 in both acidic (256 mV) and alkaline electrolytes (292 mV), long-lasting lifetime of over 2400 h (100 d), and high-temperature performance (70 oC) are due to the self-standing hydrophilic porous surface, intrinsic mechanical strength and self-grown MoC (001)-Mo2C (101) heterojunctions that have a ΔGH* value of -0.13 eV in acidic condition, and the energy barrier of 1.15 eV for water dissociation in alkaline solution. The preparation of a large electrode (3 cm × 11.5 cm) demonstrates the possibility of scaling up this process to prepare various carbide electrodes with rationally designed structures, tunable compositions, and favorable properties

Highly Stable Single-Phase FeCoNiMnX (X = Cr, Mo, W) High-Entropy Alloy Catalysts with Submicrometer Size for Efficient Oxygen Evolution

The activity and stability of oxygen evolution reaction (OER) catalysts are often trade-offs and are both size-dependent. Theoretical calculations have predicted that some noble-metal-free high-entropy alloys (HEAs) are promising OER catalysts. However, their catalytic properties have not been proven because of the lack of a facile method to synthesize small-sized homogeneous HEA particles. Here, submicrometer-sized single-phase FeCoNiMnW HEA particles were prepared by electrochemical metallization in 900 s (at 900 °C). FeCoNiMnW shows the best OER activity (η = 355 mV at 500 mA cm–2) and durability of the three HEAs because the large total density of states of FeCoNiMnW accelerates the electrons’ transport speed for OER. More importantly, the single-phase FeCoNiMnW continuously operated for 50 days at 500 mA cm–2 with an almost unchanged overpotential. Overall, this work offers a rapid and simple method to prepare various effective and long-lasting single-phase HEA catalysts with controllable sizes and enhanced OER performances

An iron-base oxygen-evolution electrode for high-temperature electrolyzers

A low-cost and efficient high-temperature oxygen evolution reaction electrode is a big challenge. Here, the authors report an iron-base electrode with an in situ formed lithium ferrite for enhanced stability and catalytic activity in molten carbonate and chloride salts and achieve kiloampere-scale electrolysis

Extracting Oxygen from Chang’e‑5 Lunar Regolith Simulants

Harvesting oxygen and metals from the local resources of the Moon is a key step to advancing outer space exploration. A large amount of oxygen is stored in the lunar regolith in the form of oxides. Many efforts have been devoted to electrochemically splitting oxides to oxygen and metals in molten oxides and molten salts. However, a cheap oxygen-evolution inert anode is still a serious challenge, especially in the supercorrosive molten halides. Herein, we combine a molten CaCl2 electrolyzer that can convert Chang’e-5 lunar regolith simulants to metals and CO2 using a carbon anode and a molten carbonate electrolyzer that can convert the generated CO2 to carbon and oxygen using a cheap Ni11Fe10Cu oxygen-evolution anode. Further, the electrolytic carbon is reused as the anode in the molten CaCl2 electrolyzer, thereby closing the carbon cycle. Hence, the overall electrochemical reaction of the dual-electrolyzer system is to convert lunar regolith to metals and oxygen. More broadly, this system can convert the CO2 generated by humans living on the Moon and Mars to oxygen and carbon materials