J.I. Paredes’s research while affiliated with Carbon Science and Technology Institute and other places

Owing to their high surface area, tunable pore size/hydrophilicity and good electrical conductivity, porous carbons are intensively investigated as a cathode material for aqueous zinc-ion hybrid capacitors (AZICs). Still, the correlation between these features and cathode performance has remained relatively underexplored. Here, we investigate a set of porous carbons with different characteristics as AZIC cathodes, and reveal how their properties impact some of their key performance metrics, such as capacity and rate capability. The minimum pore width that took part in AZIC charge storage was estimated to be ~0.65 nm by a methodology that is generally applicable to other types of capacitors and electrolytes. The effect of pore width on rate capability was also explored. Specifically, supermicropores (0.7–2 nm wide) contributed to rate capability only up to moderately high current densities (< 5 A g-1), the presence of small mesopores being required to provide significant capacity retention at higher currents. Further, the hydrophilicity of the porous carbons was quantitatively evaluated in the form of an areal density of hydrophilic sites from the analysis of water adsorption isotherms. However, this parameter did not have any noticeable impact on their performance as AZIC cathodes, at least in the areal density range investigated here.

This study presents a novel approach for boosting the selectivity of 5-hydroxymethylfurfural (HMF) production from glucose through electrochemical modification of graphite materials. Three distinct graphitic substrates were subjected to controlled electrochemical treatments utilizing sodium sulfate or phosphoric acid as electrolytes. The process expanded the graphite particles/pieces and introduced oxygenated functional groups to the exposed surfaces while preserving the structural integrity of the bulk material. The resulting modifications influenced the type and quantity of Lewis and Brønsted acidic sites, providing exhaustive control over reaction pathways leading to HMF. This electrochemically modified graphite demonstrated superior tunability compared to traditional metal-based catalysts, enabling dynamic optimization of reaction conditions for enhanced HMF yield. The controlled introduction of functional groups facilitated the tailoring of active sites, significantly impacting the kinetics of glucose conversion and achieving HMF selectivity up to 95%. This level of precision in controlling catalytic properties is essential for maximizing HMF yield while minimizing undesired by-product formation, addressing a critical challenge in HMF production.

Aqueous zinc-ion batteries (AZiBs) have emerged as a promising alternative to lithium-ion batteries as energy storage systems from renewable sources. Manganese hexacyanoferrate (MnHCF) is a Prussian Blue analogue that exhibits the ability to insert divalent ions such as Zn²⁺. However, in an aqueous environment, MnHCF presents weak structural stability and suffers from manganese dissolution. In this work, zinc doping is explored as a strategy to provide the structure with higher stability. Thus, through a simple and easy-to-implement approach, it has been possible to improve the stability and capacity retention of the cathode, although at the expense of reducing the specific capacity of the system. By correctly balancing the amount of zinc introduced into the MnHCF it is possible to reach a compromise in which the loss of capacity is not critical, while better cycling stability is obtained.

The preparation of 2H-phase MoS2 thin nanosheets by electrochemical delamination remains a challenge, despite numerous efforts in this direction. In this work, by choosing appropriate intercalating cations for cathodic delamination, the insertion process was facilitated, leading to a higher degree of exfoliation while maintaining the original 2H-phase of the starting bulk MoS2 material. Specifically, trimethylalkylammonium cations were tested as electrolytes, outperforming their bulkier tetraalkylammonium counterparts, which have been the focus of past studies. The performance of novel electrochemically derived 2H-phase MoS2 nanosheets as electrode material for electrochemical energy storage in lithium-ion batteries was investigated. The lower thickness and thus higher flexibility of cathodically exfoliated MoS2 promoted better electrochemical performance compared to liquid-phase and ultrasonically assisted exfoliated MoS2, both in terms of capacity (447 vs. 371 mA·h·g⁻¹ at 0.2 A·g⁻¹) and rate capability (30% vs. 8% capacity retained when the current density was increased from 0.2 A·g⁻¹ to 5 A·g⁻¹), as well as cycle life (44% vs. 17% capacity retention at 0.2 A·g⁻¹ after 580 cycles). Overall, the present work provides a convenient route for obtaining MoS2 thin nanosheets for their advantageous use as anode material for lithium storage.

Graphene materials are attractive for use in novel aqueous electrochemical energy storage devices, including aqueous zinc-ion batteries (AZIBs) and hybrid capacitors (AZICs). Ideally, such materials should be readily accessible by eco-friendly routes and possess physicochemical features beneficial for the intended application. Here, we propose an anodic exfoliation strategy, using a proper combination of common salts/bases as the aqueous electrolyte, for the preparation of highly oxidized graphenes with some control over the populations of their oxygen groups and retention of electrical conductivity (~102–103 S m-1). As an active cathode material for AZIC cells, the hydrophilic, carboxyl-enriched anodic graphene processed into a compact film outperformed reduced graphene oxides derived from common routes (e.g., Hummers method), in terms of capacity and rate capability. Furthermore, the performance of this new anodic graphene was enhanced by combining it with a multifunctional biomolecule (flavin mononucleotide), which promoted the cathode wettability and provided extra capacity due to its redox-active center, particularly at higher currents. The carboxyl-enriched graphene was also shown to act as an effective coating layer for the protection of the zinc metal electrode in AZICs/AZIBs, extending its cycle life for longer than is usually attained with carbon-based protective coatings.

Layered transition-metal dichalcogenides (LTMDs) in two-dimensional (2D) form are attractive for electrochemical energy storage, but research efforts in this realm have so far largely focused on the best-known members of such a family of materials, mainly MoS2, MoSe2, and WS2. To exploit the potential of further, currently less-studied 2D LTMDs, targeted methods for their production, preferably by cost-effective and sustainable means, as well as control over their nanomorphology, are highly desirable. Here, we report a quick and straightforward route for the preparation of 2D NbSe2 and other metallic 2D LTMDs that relies on delaminating their bulk parent solid under aqueous cathodic conditions. Unlike typical electrochemical exfoliation methods for 2D materials, which generally require an additional processing step (e.g., sonication) to complete delamination, the present electrolytic strategy yielded directly exfoliated nano-objects in a very short time (1-2 min) and with significant yields (∼16 wt %). Moreover, the dominant morphology of the exfoliated 2D NbSe2 products could be tuned between rolled-up nanosheets (nanorolls) and unfolded nanosheets, depending on the solvent where the nano-objects were dispersed (water or isopropanol). This rather unusual delamination behavior of NbSe2 was explored and concluded to occur via a redox mechanism that involves some degree of hydrolytic oxidation of the material triggered by the cathodic treatment. The delamination strategy could be extended to other metallic LTMDs, such as NbS2 and VSe2. When tested toward electrochemical lithium storage, electrodes based on the exfoliated NbSe2 products delivered very high capacity values, up to 750-800 mA h g-1 at 0.5 A g-1, where the positive effect of the nanoroll morphology, associated to increased accessibility of the lithium storage sites, was made apparent. Overall, these results are expected to expand the availability of fit-for-purpose 2D LTMDs by resorting to simple and expeditious production strategies of low environmental impact.