Sulfidation of nickel foam with enhanced electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

Nickel-phytic acid hybrid for highly efficient electrocatalytic upgrading of HMF

Electrocatalytic upgrading of 5-hydroxymethylfurfural (HMF) provides a promising way to obtain both high-value-added biomass-derived chemicals and clean energy. However, development of efficient electrocatalysts for oxidizing HMF with depressed side reactions remains a challenge. Herein, we report a nickel-phytic acid hybrid (Ni-PA) using natural phytic acid as building block for highly efficient electrocatalytic oxidation of HMF to 2, 5-furandicarboxylic acid (FDCA). Due to the coordination of nickel ion and phosphate groups of phytic acid molecule, high selectivity and yield of FDCA were achieved at 1.6 V vs. RHE. Besides, Ni-PA has a higher electrochemical surface area and lower charge-transfer resistance than Cu/Fe-PA, which significantly promotes the oxidation of HMF to FDCA. This work demonstrates the potential of metal-phytic acid hybrids as effective electrocatalysts for biomass valorization.

MIL-47(V)-derived carbon-doped vanadium oxide for selective oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran

The development and transformation of biomass-derived platform compounds is a sustainable way to deal with the fossil fuel crisis. 5-Hydroxymethylfurfural (HMF) can be reduced or oxidized to produce many high-value compounds; however, it is challenging to effectively produce 2,5-diformylfuran (DFF) due to overoxidation. In this work, a carbon-doped V₂O₅ (C-V₂O₅) material was obtained through pyrolysis of MIL-47(V) nanorods, a typical metal-organic framework material. The X-ray diffraction patterns and X-ray photoelectron spectra showed that the graphitized carbon species were incorporated in C-V₂O₅. High-efficiency HMF oxidation, high specific selectivity for DFF and excellent recycling could be achieved with the C-V₂O₅ catalyst. Fourier-transform infrared spectroscopy combined with density functional theory (DFT) calculation revealed that graphitized carbon weakens the VO bond and promotes the formation of oxygen vacancies in C-V₂O₅, thus improving the catalytic activity in the oxidation of furfuryl alcohols. The V⁴⁺ induced by oxygen vacancies will be oxidized by O₂ to form V⁵⁺, so that the cycle can be realized. It exhibits remarkable selectivity in the oxidation of different alcohols produced from biomass based on the relatively constant active sites in C-V₂O₅.

Alloy-Driven Efficient Electrocatalytic Oxidation of Biomass-Derived 5-Hydroxymethylfurfural towards 2,5-Furandicarboxylic Acid: A Review

In recent years, electrocatalysis was progressively developed to facilitate the selective oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) towards the value-added chemical 2,5-furandicarboxylic acid (FDCA). Among reported electrocatalysts, alloy materials have demonstrated superior electrocatalytic properties due to their tunable electronic and geometric properties. However, a specific discussion of the potential impacts of alloy structures on the electrocatalytic HMF oxidation performance has not yet been presented in available Reviews. In this regard, this Review introduces the most recent perspectives on the alloy-driven electrocatalysis for HMF oxidation towards FDCA, including oxidation mechanism, alloy nanostructure modulation, and external conditions control. Particularly, modulation strategies for electronic and geometric structures of alloy electrocatalysts have been discussed. Challenges and suggestions are also provided for the rational design of alloy electrocatalysts. The viewpoints presented herein are anticipated to potentially contribute to a further development of alloy-driven electrocatalytic oxidation of HMF towards FDCA and to help boost a more sustainable and efficient biomass refining system.

Electrochemically Derived Crystalline CuO from Covellite CuS Nanoplates: A Multifunctional Anode Material

In the present era, electrochemical water splitting has been showcased as a reliable solution for alternative and sustainable energy development. The development of a cheap, albeit active, catalyst to split water at a substantial overpotential with long durability is a perdurable challenge. Moreover, understanding the nature of surface-active species under electrochemical conditions remains fundamentally important. A facile hydrothermal approach is herein adapted to prepare covellite (hexagonal) phase CuS nanoplates. In the covellite CuS lattice, copper is present in a mixed-valent state, supported by two different binding energy values (932.10 eV for Cu^I and 933.65 eV for Cu^II) found in X-ray photoelectron spectroscopy analysis, and adopted two different geometries, that is, trigonal planar preferably for Cu^I and tetrahedral preferably for Cu^II. The as-synthesized covellite CuS behaves as an efficient electro(pre)catalyst for alkaline water oxidation while deposited on a glassy carbon and nickel foam (NF) electrodes. Under cyclic voltammetry cycles, covellite CuS electrochemically and irreversibly oxidized to CuO, indicated by a redox feature at 1.2 V (vs the reversible hydrogen electrode) and an ex situ Raman study. Electrochemically activated covellite CuS to the CuO phase (termed as CuS_EA) behaves as a pure copper-based catalyst showing an overpotential (η) of only 349 (±5) mV at a current density of 20 mA cm^-2, and the TOF value obtained at η₃₄₉ (at 349 mV) is 1.1 × 10^-3 s^-1. A low R_ct of 5.90 Ω and a moderate Tafel slope of 82 mV dec^-1 confirm the fair activity of the CuS_EA catalyst compared to the CuS precatalyst, reference CuO, and other reported copper catalysts. Notably, the CuS_EA/NF anode can deliver a constant current of ca. 15 mA cm^-2 over a period of 10 h and even a high current density of 100 mA cm^-2 for 1 h. Post-oxygen evolution reaction (OER)-chronoamperometric characterization of the anode via several spectroscopic and microscopic tools firmly establishes the formation of crystalline CuO as the active material along with some amorphous Cu(OH)₂ via bulk reconstruction of the covellite CuS under electrochemical conditions. Given the promising OER activity, the CuS_EA/NF anode can be fabricated as a water electrolyzer, Pt(-)//(+)CuS_EA/NF, that delivers a j of 10 mA cm^-2 at a cell potential of 1.58 V. The same electrolyzer can further be used for electrochemical transformation of organic feedstocks like ethanol, furfural, and 5-hydroxymethylfurfural to their respective acids. The present study showcases that a highly active CuO/Cu(OH)₂ heterostructure can be constructed in situ on NF from the covellite CuS nanoplate, which is not only a superior pure copper-based electrocatalyst active for OER and overall water splitting but also for the electro-oxidation of industrial feedstocks.

W exsolution promotes the in situ reconstruction of a NiW electrode with rich active sites for the electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF)

W exsolution induces surface defects, promoting the in situ self-reconstruction and formation of high-valance Ni with superior activity towards HMFOR.

Electroreforming of Biomass for Value-Added Products

Humanity's overreliance on fossil fuels for chemical and energy production has resulted in uncontrollable carbon emissions that have warranted widespread concern regarding global warming. To address this issue, there is a growing body of research on renewable resources such as biomass, of which cellulose is the most abundant type. In particular, the electrochemical reforming of biomass is especially promising, as it allows greater control over valorization processes and requires milder conditions. Driven by renewable electricity, electroreforming of biomass can be green and sustainable. Moreover, green hydrogen generation can be coupled to anodic biomass electroforming, which has attracted ever-increasing attention. The following review is a summary of recent developments related to electroreforming cellulose and its derivatives (glucose, hydroxymethylfurfural, levulinic acid). The electroreforming of biomass can be achieved on the anode of an electrochemical cell through electrooxidation, as well as on the cathode through electroreduction. Recent advances in the anodic electroreforming of cellulose and cellulose-derived glucose and 5-hydrooxylmethoylfurural (5-HMF) are first summarized. Then, the key achievements in the cathodic electroreforming of cellulose and cellulose-derived 5-HMF and levulinic acid are discussed. Afterward, the emerging research focusing on coupling hydrogen evolution with anodic biomass reforming for the cogeneration of green hydrogen fuel and value-added chemicals is reviewed. The final chapter of this paper provides our perspective on the challenges and future research directions of biomass electroreforming.