One Stone Three Birds: An Aqueous Mg–CO₂ Battery for Generation of Electricity, Syngas, and High-Value Phosphate

Abstract

Mg–CO2 battery as a promising strategy for CO2 conversion and utilization is challenging, owing to the sluggish kinetics of CO2 reduction reaction (CO2RR) and the waste of the sacrificial Mg anode. Herein, by elaborately designing a highly selective Ni NPs/Ni–N–C SACs electrocatalyst toward CO2RR and rationally optimizing the electrolyte, an effective aqueous-phase Mg–CO2 battery is demonstrated to generate not only electricity, but also syngas with CO from the CO2RR and H2 from the chemical oxidation of Mg, together with higher-valued MgHPO4 phosphate. Notably, the output of electricity, the proportion of CO/H2 in syngas, and the yields/crystalline quality of MgHPO4 can be well regulated by manipulating the operation parameters. The Mg–CO2 battery generates a favorable open-circuit voltage of 1.44 V with a peak power density of 2.91 mW cm–2. Under the optimal condition, the Ni NPs/Ni–N–C SACs catalyst displays both a high FECO of 98.12% at −0.573 VRHE and a high CO2-to-CO current of −20.73 mA cm–2 at −0.973 VRHE, owing to the synergistic effect between Ni particles and Ni–N moieties. The proposed Mg–CO2 battery provides an intriguing approach for CO2 conversion and utilization in off-grid, with the advantage of coproduction of higher-valued chemicals at both electrodes.

Recent Advances in Rechargeable Metal–CO2 Batteries with Nonaqueous Electrolytes

“…The 12 th element in the periodic table, Mg, has also been drawing significant attention from researchers for developing metal–CO 2 batteries. Apart from the Mg–O 2 batteries, − recently, a few reports on Mg–CO 2 have also started coming. − Mg offers advantages like adequate natural abundance, cost-effectiveness, and high theoretical volumetric capacity (3833 mAh/cm 3 ) and theoretical specific capacity (2205 mAh/g). Moreover, unlike Li, Na, and K, the Mg metal anode does not give rise to dendrite formationoffering better safety and stability.…”

Understanding Catalytic Mechanisms and Cathode Interface Kinetics in Nonaqueous Mg–CO2 Batteries

“…Li–CO 2 batteries have garnered interest as a potential source of high energy density for electrochemical energy storage systems (ESSs), utilizing the power of CO 2 . − However, the limited availability and geographically localized distribution of lithium, along with its high cost, present significant challenges that hinder the widespread adoption of Li–CO 2 batteries. , Furthermore, the high reactivity of alkali metals, combined with their propensity for dendrite formation during cycling, gives rise to notable safety concerns, diminishes battery cycle life, and imposes practical limitations on their utility. − Considering its high volumetric energy density, excellent safety profile, environmental friendliness, and cost-effectiveness, the rechargeable Mg–CO 2 battery is regarded as a promising solution for efficient energy storage and effective CO 2 utilization. , …”

“…19−21 Considering its high volumetric energy density, excellent safety profile, environmental friendliness, and cost-effectiveness, the rechargeable Mg−CO 2 battery is regarded as a promising solution for efficient energy storage and effective CO 2 utilization. 19,22 The nonaqueous Mg−CO 2 battery demonstrates a promising perspective, distinguished by its ability to store energy utilizing low-cost and high-capacity Mg anode and consuming CO 2 . 19,22,23 However, the development of Mg−CO 2 batteries is currently facing significant obstacles such as limited rate capability, reduced energy efficiency, and shortened cycle life.…”

“…19,22 The nonaqueous Mg−CO 2 battery demonstrates a promising perspective, distinguished by its ability to store energy utilizing low-cost and high-capacity Mg anode and consuming CO 2 . 19,22,23 However, the development of Mg−CO 2 batteries is currently facing significant obstacles such as limited rate capability, reduced energy efficiency, and shortened cycle life. Thus far, there is limited study on Mg−CO 2 batteries employing nonaqueous electrolytes or functioning without any assistance from H 2 O.…”

“…There have been several advances in the cathode materials to reduce charge–discharge overpotential and improve the round-trip energy efficiency of alkali metal–CO 2 batteries since the commencement of metal–CO 2 battery research over a decade ago. ,,, Carbonaceous materials, including ketjen black (KB), are widely employed as cathode matrices in metal–CO 2 batteries due to their favorable attributes such as high electrical conductivity, chemical stability, and adjustable surface area. − However, the catalytic performance of nonpolar carbon materials is limited. To address this, recent research has focused on developing heteroatom-doped and nanostructured carbon materials.…”