Nanoengineering Carbonaceous Materials: A Multifunctional Platform towards a Greener Energy Future

摘要

The search for sustainable, net-zero carbon sources of energy has been a long-standing global agenda for tackling the on-going climate crisis. This has become more pressing with the recently released special report by the United Nations Intergovernmental Panel on Climate Change (IPCC), highlighting that a global rise in temperature of 1.5 °C is likely to occur at the current rate of CO2 emissions.[1] The United Nations also stated that a global coalition must be built to reach carbon neutrality by 2050 before irreversible damage is dealt to our ecosystem.[2] To address this crisis, research on carbonaceous materials as energy storage and conversion materials has been outlined as a solution avenue as they are cost-effective, abundant, environmentally benign materials with a multitude of bonding states and allotropes (Figure 1). Some examples of such materials are graphene, carbon nanotubes (CNTs), graphitic carbon nitride (g-C3N4), and graphdiyne, which also come in a variety of morphological configurations. However, there still exist many challenges that lie in both the materials processing and application performance. Thus, this special issue themed "Nanoengineering Carbonaceous Materials for Energy" consists of 17 reviews, 6 concept papers and 8 original research papers, which cover the recent progress and challenges in the design, synthesis and applications of carbon-based materials for energy applications. To address the environmental woes, there has been a rise in interest in the development of photocatalytic materials that utilize the abundant solar energy for environmental remediation applications. This is highlighted in a review by Centi et al. (10.1002/smll.202007055), who summarize the recent progress in nanocarbons for the direct synthesis of ammonia from N2 (i.e. N2 reduction reaction). The authors suggest a holistic approach that takes into consideration all functional elements, including the activation of N2, charge transfer to the chemisorbed N2 and reaction intermediates, charge separation and light harvesting, and the reconstruction of active sites during the reaction due to an applied voltage/surface potential. Meanwhile, the hydrogen evolution reaction (HER) through electrochemical water splitting has shown promise as an avenue for renewable energy production. Despite the high electrocatalytic activities of metal-free carbon materials, there still exists a big gap in HER performance between carbon and metal-based electrocatalysts. Hui et al. (10.1002/smll.202006136) aim to bridge this gap by developing graphdiyne, a 2D carbon monolayer comprising sp2 and sp-hybridized carbon atoms, into a 3D carbon fiber network as a model electrocatalyst to assess the HER activity at an atomic level. The 3D porous conductive substrate is found to be beneficial for efficient mass transport and gas release as well as providing a large electrocatalytic surface area. Although renewable energy research such as solar energy has been gaining momentum, one notable problem is that its availability is inconsistent throughout the year and world. Thus, a high-capacity energy storage device should be developed to go in conjunction with the rise in renewable technology. Schutjajew et al. report the influence of pore architecture and chemical structure on nitrogen-doped hard carbons in sodium ion batteries (10.1002/smll.202006767). The introduction of nitrogen is found to positively influence the adsorption of sodium by binding the sodium ions at the edge/defect sites, while the porous structure motifs stabilize sodium within its domain. As a result, the system has a high stability with 90% of the bulk sodiation capacity being maintained after five cycles. Zhang et al. synthesize well-dispersed hollow porous carbon nanofibers (HPCNs) as sulfur hosts for Li-S batteries (10.1002/smll.202004140). The HPCNs are able to encapsulate sulfur within their porous structure, endowing it with excellent cycling performance with an 89% capacity retenti