Abstract
Electrocatalytic CO
2
reduction to value-added hydrocarbon products using metallic copper (Cu) catalysts is a potentially sustainable approach to facilitate carbon neutrality. However, Cu ...metal suffers from unavoidable and uncontrollable surface reconstruction during electrocatalysis, which can have either adverse or beneficial effects on its electrocatalytic performance. In a break from the current catalyst design path, we propose a strategy guiding the reconstruction process in a favorable direction to improve the performance. Typically, the controlled surface reconstruction is facilely realized using an electrolyte additive, ethylenediamine tetramethylenephosphonic acid, to substantially promote CO
2
electroreduction to CH
4
for commercial polycrystalline Cu. As a result, a stable CH
4
Faradaic efficiency of 64% with a partial current density of 192 mA cm
−2
, thus enabling an impressive CO
2
-to-CH
4
conversion rate of 0.25 µmol cm
−2
s
−1
, is achieved in an alkaline flow cell. We believe our study will promote the exploration of electrochemical reconstruction and provide a promising route for the discovery of high-performance electrocatalysts.
Tin and its compounds hold promise for the development of high-capacity anode materials that could replace graphitic carbon used in current lithium-ion batteries. However, the introduced porosity in ...current electrode designs to buffer the volume changes of active materials during cycling does not afford high volumetric performance. Here, we show a strategy leveraging a sulfur sacrificial agent for controlled utility of void space in a tin oxide/graphene composite anode. In a typical synthesis using the capillary drying of graphene hydrogels, sulfur is employed with hard tin oxide nanoparticles inside the contraction hydrogels. The resultant graphene-caged tin oxide delivers an ultrahigh volumetric capacity of 2123 mAh cm
together with good cycling stability. Our results suggest not only a conversion-type composite anode that allows for good electrochemical characteristics, but also a general synthetic means to engineering the packing density of graphene nanosheets for high energy storage capabilities in small volumes.
Killer applications of graphenes are always being pursued and critical for realizing industrialization. Since the first attempt for using graphene in lithium‐ion batteries, graphene has been ...demonstrated as a key component in electrochemical energy storage technologies. However, the unique roles of graphene beyond traditional carbon in energy storage are still unclear and need to be clarified. Here, this review starts with a glance over the history of graphene in electrochemical energy storage applications, and then briefly discusses the different dimensional graphenes and representative synthesis methods that are believed to be essential for energy‐related applications. Importantly, three typical graphene technologies showing their practical potentials in electrochemical energy storage are illustrated in details, including the uses as conductive additives, in heat dissipation, and compact energy storage. The methodologies of science and technology for the above applications are systematically elaborated. This review also gives perspectives on the opportunities and challenges of practical graphene technologies in electrochemical energy storage. The authors expect this review to provide a comprehensive view of how graphene can be uniquely and practically used for electrochemical energy storage, paving the way for promoting the development of the graphene industry.
Pursuing killer applications of graphenes is the core topic that determines the future of graphene industry. This review systematically discusses how graphenes can be uniquely and practically used for electrochemical energy storage compared to traditional carbon materials, and illustrates their promising killer uses for advanced batteries with three typical examples such as conductive additives, heat dissipation and compact energy storage.
Supercapacitors are increasingly in demand among energy storage devices. Due to their abundant porosity and low cost, activated carbons are the most promising electrode materials and have been ...commercialized in supercapacitors for many years. However, their low packing density leads to an unsatisfactory volumetric performance, which is a big obstacle for their practical use where a high volumetric energy density is necessary. Inspired by the dense structure of irregular pomegranate grains, a simple yet effective approach to pack activated carbons into a compact graphene network with graphene as the “peels” is reported here. The capillary shrinkage of the graphene network sharply reduces the voids between the activated carbon particles through the microcosmic rearrangement while retaining their inner porosity. As a result, the electrode density increases from 0.41 to 0.76 g cm−3. When used as additive‐free electrodes for supercapacitors in an ionic liquid electrolyte, this porous yet dense electrode delivers a volumetric capacitance of up to 138 F cm−3, achieving high gravimetric and volumetric energy densities of 101 Wh kg−1 and 77 Wh L−1, respectively. Such a graphene‐assisted densification strategy can be extended to the densification of other carbon or noncarbon particles for energy devices requiring a high volumetric performance.
Inspired by the dense structure of irregular pomegranate grains, a densification strategy of activated carbons (ACs) is proposed by packing them into a compact graphene network with graphene as the “peels.” The capillary shrinkage of the graphene network sharply reduces the voids between AC particles while retaining their inner porosity. It shows great promise for high volumetric performance supercapacitors.
Dual-doping of carbon, especially the combination of nitrogen and a secondary heteroatom, has been demonstrated efficient to optimize the oxygen reduction reaction (ORR) performance. However, the ...optimum dual-doping is still not clear due to the lack of strong experimental proofs, which rely on a reliable method to prepare carbon materials that can rule out the interference factors and then emphasize only the doping effects. In this work, an inside-out doping method is reported to prepare carbon submicrotubes (CSTs) as a material to study the principles of designing dual-doping catalysts for ORR. The interference factors including the metal impurities and doping gradient in the bulk phase are excluded, and the doping effects including the structural and chemical variation of carbon are studied. P-doping exhibited a higher pore-forming ability to perforate carbon and a lower doping content, but a higher ORR catalytic activity as compared with S- and B-doped N-CSTs, demonstrating the N,P co-doping is more efficient in making carbon-based catalysts for ORR. First-principle calculations reveal that the edge C situated around the oxidized P site nearby a graphitic N atom is the active site that shows the lowest ORR overpotential comparable to Pt-based catalysts. This study suggests that the catalytic activity of dual-heteroatoms-doped carbons not only depends on the intrinsic chemical bonding between heteroatoms and carbon, but also is affected by the structural variation generated by introducing different atoms, which can be extended to the study of other kinds of functionalization of carbon and potential reactions besides ORR.
Rechargeable aqueous zinc (Zn) ion‐based energy storage systems have been reviving recently because of their low cost and high safety merits; however, they still suffer from the problems of corrosion ...and dendrite growth on Zn metal anodes that cause gas generation and early battery failure. Unfortunately, the corrosion problem has not received sufficient attention until now. Here, it is pioneeringly demonstrated that decorating the Zn surface with a dual‐functional metallic indium (In) layer, acting as both a corrosion inhibitor and a nucleating agent, is a facile but effective strategy to suppress both drastic corrosion and dendrite growth. Symmetric cells assembled with the treated Zn electrodes can sustain up to 1500 h of plating/stripping cycles with an ultralow voltage hysteresis (54 mV), and a 5000 cycle‐life is achieved for a prototype full cell. This work will instigate the further development of aqueous metal‐based energy storage systems.
A dual‐functional metallic In layer is in situ decorated on the Zn anode surface, acting as both a corrosion inhibitor and a nucleating agent, to suppress both drastic corrosion and dendrite growth. Symmetric cells assembled with the treated Zn electrodes can sustain up to 1500 h of plating/stripping cycles with an ultralow voltage hysteresis (54 mV).
Gelation is an effective way to realize the self‐assembly of nanomaterials into different macrostructures, and in a typical use, the gelation of graphene oxide (GO) produces various graphene‐based ...carbon materials with different applications. However, the gelation of MXenes, another important type of 2D materials that have different surface chemistry from GO, is difficult to achieve. Here, the first gelation of MXenes in an aqueous dispersion that is initiated by divalent metal ions is reported, where the strong interaction between these ions and OH groups on the MXene surface plays a key role. Typically, Fe2+ ions are introduced in the MXene dispersion which destroys the electrostatic repulsion force between the MXene nanosheets in the dispersion and acts as linkers to bond the nanosheets together, forming a 3D MXene network. The obtained hydrogel effectively avoids the restacking of the MXene nanosheets and greatly improves their surface utilization, resulting in a high rate performance when used as a supercapacitor electrode (≈226 F g−1 at 1 V s−1). It is believed that the gelation of MXenes indicates a new way to build various tunable MXene‐based structures and develop different applications.
Fast gelation of Ti3C2Tx MXenes is initiated by divalent metal ions in aquesous solution. Typically, Fe2+ ions eliminate the electrostatic repulsion, networking MXene nanosheets into a 3D structured hydrogel. The wet hydrogel avoids nanosheet restacking and is ideal for applications highlighting the surface utilization, especially as freestanding electrodes for high‐rate supercapacitors.
Aqueous zinc batteries, that demonstrate high safety and low cost, are considered promising candidates for large‐scale energy storage. However, Zn anodes suffer from rapid performance deterioration ...due to the severe Zn dendrite growth and side reactions. Herein, with a low‐cost ammonium acetate (NH4OAc) additive, a self‐regulated Zn/electrolyte interface is built to address these problems. The NH4+ induces a dynamic electrostatic shielding layer around the abrupt Zn protuberance to make the Zn deposition uniform, and the OAc− acts as an interfacial pH buffer to suppress the proton‐induced side reactions and the precipitation of insoluble by‐products. As a result, in the electrolyte with the NH4OAc additive, Zn anodes exhibit a long cycling stability of 3500 h at 1 mA cm−2, an impressive cumulative areal capacity of 5000 mAh cm−2 at 10 mA cm−2, and a high Coulombic efficiency of ≈99.7%. A prototype full cell coupled with a NH4V4O10 cathode performs much better in terms of capacity retention than the additive‐free case. The findings pave the way for developing practical Zn batteries.
A self‐regulated interface is built using a dual‐functional ammonium acetate additive to address zinc dendrite growth and proton‐induced side reactions simultaneously, thus enabling an Zn anode with long cycling stability of 3500 h, an impressive cumulative areal capacity of 5000 mAh cm−2 at 10 mA cm−2, and a high Coulombic efficiency of 99.7%.
In aqueous zinc (Zn) batteries, the Zn anode suffers from severe corrosion reactions and consequent dendrite growth troubles that cause fast performance decay. Herein, we uncover the corrosion ...mechanism and confirm that the dissolved oxygen (DO) other than the reputed proton is a principal origin of Zn corrosion and by‐product precipitates, especially during the initial battery resting period. In a break from common physical deoxygenation methods, we propose a chemical self‐deoxygenation strategy to tackle the DO‐induced hazards. As a proof of concept, sodium anthraquinone‐2‐sulfonate (AQS) is introduced to aqueous electrolytes as a self‐deoxidizing additive. As a result, the Zn anode sustains a long‐term cycling of 2500 h at 0.5 mA cm−2 and over 1100 h at 5 mA cm−2 together with a high Coulombic efficiency up to 99.6 %. The full cells also show a high capacity retention of 92 % after 500 cycles. Our findings provide a renewed understanding of Zn corrosion in aqueous electrolytes and also a practical solution towards industrializing aqueous Zn batteries.
Dissolved oxygen (DO) is a major cause of Zn corrosion and by‐product precipitation during battery resting, usually attributed to protons. To tackle DO‐induced issues, a chemical strategy for self‐deoxygenation is proposed. As a proof of concept, sodium anthraquinone‐2‐sulfonate (AQS) is introduced as a self‐deoxidizing additive, effectively improving the stability of Zn in aqueous electrolytes.
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