Microbial electrosynthesis (MES) is an emerging technology that enables the synthesis of value-added chemicals from carbon dioxide (CO2) or inorganic carbon compounds by coupling renewable electricity to microbial metabolism. However, MES still faces challenges in achieving high production of value-added chemicals due to the limited extracellular electron transfer efficiency at the biotic-abiotic interfaces. To overcome this bottleneck, it is crucial to develop novel cathodes and modified materials. This review systematically summarizes recent advancements in cathode materials in the field of electrocatalyst-assisted and photocatalyst-assisted MES. The effects of various material types are further investigated by comparing metal-free and metal materials and photocatalyst materials of different semiconductor types. Additionally, the review introduces the maximum production rate of value-added chemicals and conversion efficiency achieved by these cathode materials while highlighting the advantages and disadvantages of different material types. To the best of our knowledge, in electrocatalyst-assisted systems, the maximum CH4 yield on graphene aerogel/polypyrrole cathode achieved 1,672 mmol m-2 d-1, and the maximum Faraday efficiency (FE) of CH4 reached up to 97.5% on graphite plate. Meanwhile, the maximum acetate yield achieved 1,330 g m-2 d-1 with CO2 conversion efficiency into acetate close to 100% on carbon nanotube cathodes. In photocatalyst-assisted systems, the maximum acetate yield could reach 0.51 g L-1 d-1 with the coulombic efficiency of 96% on the MnFe2O4/g-C3N4 photocathode. Finally, prospects for future development and practical applications of MES are discussed, offering theoretical guidance for the fabrication of cathode materials that can improve production efficiency and reduce energy input.
Rechargeable potassium-ion batteries (PIBs) have gained attention as sustainable, environmentally friendly, and cost-effective large-scale stationary energy storage technology. However, although this technology was assumed to perform in a manner similar to that of its monovalent counterparts, huge anode volume expansion and sluggish kinetics are posing challenges in up-scaling it. Apart from the efforts to develop and optimise electrode materials, recent research endeavours have also focussed on the essential role of sustainability. These attempts have often relied on bio-derived and bio-inspired materials to mimic the effectiveness of nature. Furthermore, the use of materials with self-healing properties can alleviate electrode degradation after cycling and augment its electrochemical performance. This review summarises the development of smart materials with self-healing properties that aid in overcoming the present issues of PIBs and highlights the relevance of the interphases. In addition, state-of-the-art design strategies for bio-derived and bio-inspired materials are presented and discussed. The incorporation of recycled and sustainable materials into the manufacturing of PIBs is expected to contribute towards the ultimate goal of achieving truly circular economy ecosystems. Finally, perspectives for further advancements are provided to kindle new ideas and open questions regarding the use of new-generation materials in the development of PIBs.
Metal-organic frameworks (MOFs) have attracted increasing attention in electrochemistry due to their inherent characteristics, such as large specific surface area, high porosity, and structural flexibility. Defects can be designed and generated during the synthesis of MOFs, and their presence gives MOF materials excellent properties in terms of electrochemical energy conversion and storage. This review focuses on the types of defects in MOFs and presents recent and important advances in the methods for introducing defects into MOFs and the effects of defects on the physicochemical properties of MOFs, with emphasis on the application of defective MOFs as catalysts for electrochemical energy conversion and storage. On this basis, the current advantages and disadvantages of defective MOFs in electrochemical energy conversion and storage are presented and future research directions for defective MOFs construction in electrochemical applications are proposed.
The energy density of lithium-ion batteries based on intercalated electrode materials has reached its upper limit, which makes it challenging to meet the growing demand for high-energy storage systems. Electrode materials based on conversion reactions such as sulfur, organosulfides, and oxygen involving breakage and reformation of chemical bonds can provide higher specific capacity and energy density. In addition, they usually consist of abundant elements, making them renewable. Although they have the aforementioned benefits, they face numerous challenges for practical applications. For example, the cycled products of sulfur and molecular organosulfides could be soluble in a liquid electrolyte, resulting in the shuttle effect and significant capacity loss. The discharged product of oxygen is Li2O2, which could result in high charge overpotential and decomposition of the electrolyte. In this review, we present an overview of the current strategies for improving the performances of lithium-sulfur, lithium-organosulfide, and lithium-oxygen batteries. First, we summarize the efforts to overcome the issues facing sulfur and organosulfide cathodes, as well as the strategies to increase the capacity of organosulfides. Then, we introduce the latest research progress on catalysts in lithium-oxygen batteries. Finally, we summarize and provide outlooks for the conversion of electrode materials.
The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for dual-functional non-precious metal electrocatalysts are promising alternatives for Pt/Ru-based materials in rechargeable zinc-air batteries (ZABs). However, how to achieve dual-functional oxygen electrocatalytic activity on single-component catalysts and identify the sites responsible for ORR and OER still face many challenges. Herein, an efficient and stable dual-functional electrocatalyst is fabricated by a two-step hydrothermal method with iron phthalocyanine (FePc) π-π stacking on nickel-iron selenide layered hydroxide derivatives (Se/Ni3Se4/Fe3O4). The as-prepared multi-component catalyst (named as FePc/Se@NiFe) exhibits better oxygen electrocatalytic properties than Pt/Ru-based catalysts, with a half-wave potential (E1/2) of 0.90 V and an overpotential of 10 mA cm-2 (Ej10) of 320 mV. More importantly, chronoamperometry (I-T) and accelerated durability tests (ADT) show the unordinary stability of the catalyst. Both physical characterization and experimental results verify that the Fe-N4 moieties and Ni3Se4 crystalline phase are the main active sites for ORR and OER activities, respectively. The small potential gap (ΔE = Ej10 - E1/2 = 0.622 V) represents superior dual-functional activities of the FePc/Se@NiFe catalyst. Subsequently, the ZABs assembled using FePc/Se@NiFe exhibit excellent performances. This study offers a promising design concept for promoting further development of high-performance ORR and OER electrocatalysts and their application in ZAB.
