Carbon Nanotubes Produced from Ambient Carbon Dioxide for Environmentally Sustainable Lithium-Ion and Sodium-Ion Battery Anodes

Abstract

The cost and practicality of greenhouse gas removal processes, which are critical for environmental sustainability, pivot on high-value secondary applications derived from carbon capture and conversion techniques. Using the solar thermal electrochemical process (STEP), ambient CO2 captured in molten lithiated carbonates leads to the production of carbon nanofibers (CNFs) and carbon nanotubes (CNTs) at high yield through electrolysis using inexpensive steel electrodes. These low-cost CO2-derived CNTs and CNFs are demonstrated as high performance energy storage materials in both lithium-ion and sodium-ion batteries. Owing to synthetic control of sp3 content in the synthesized nanostructures, optimized storage capacities are measured over 370 mAh g–1 (lithium) and 130 mAh g–1 (sodium) with no capacity fade under durability tests up to 200 and 600 cycles, respectively. This work demonstrates that ambient CO2, considered as an environmental pollutant, can be attributed economic value in grid-scale and portable energy storage systems with STEP scale-up practicality in the context of combined cycle natural gas electric power generation.

Sustainable Electrochemical Synthesis of Large Grain- or Catalyst-Sized Iron

“…For the 5 A electrolysis, the production of longer iron particles is also evident from the low oxide electrolyte (bottom, left). Li 2 O concentrations have also been observed to effect the morphology of carbon nanotubes and nanofibers grown from molten Li 2 CO 3 (in the absence of added iron oxide), and specifically that higher Li 2 O concentrations lead to the growth of tangled, rather than straight nanostructures [27,28].…”

Review—Electrochemical Growth of Carbon Nanotubes and Graphene from Ambient Carbon Dioxide: Synergy with Conventional Gas-Phase Growth Mechanisms

“…al 11 The authors comment that the observed "nano ropes" observed are parallel carbon nanofibers bound together, though speculation of how the different carbon nanostructures are formed in electrolysis is not detailed in the report. In more recent years, the observation of higher quality carbon nanostructures has been studied, with the growth of few-layer graphene sheets (<5 layers) 15,16 ( Figure 5d) and carbon nanofibers with diameters >200 nm (Figure 5e) 58 in 2015, and more recently carbon nanotubes with diameters >100 nm (Figure 5f) 46 in 2016. These works begin to build upon mechanistic understandings gained from gas phase growth techniques, and start to bridge the gap between gas phase growth of carbon nanostructures and CO 2 electrolysis.…”

“…Concepts critical to the catalytic growth of CNTs have been highlighted as precursor chemistry, 31 catalyst composition and/or oxidation state, [32][33][34] catalyst size, 35 physical and chemical properties of catalyst supports, [36][37][38] growth temperature, [39][40][41] and physical processes during growth such as Ostwald ripening, catalyst diffusion, and mechanically driven collective growth termination processes. [42][43][44][45] In contrast to this mature field, the growth of carbon nanostructures from the liquid-phase electrochemical reduction of CO 2 remains only a new field of research, with the most recent work demonstrating growth of large-diameter (>100 nm) CNTs 46 and fewlayer graphene flakes from CO 2 conversion. 15,16 These initial works demonstrate the capability to leverage CO 2 as a precursor in carbon nanostructure growth, even though forward-looking efforts to achieve high quality, precisely tuned materials such as single-walled CNTs or single-layered graphene at high yields will require control of the process beyond the systems-level approaches reported so far.…”

Introduction

“…Given their extensive surface area, CNTs can easily be conjugated with a large range of different biological molecules (e.g. enzymes, proteins, nucleic acids, etc) [17,19,21,22]. van der Waals interactions hold together the individual rolledgraphene sheets, creating large aggregates that resemble bunches of asparagus.…”