Highly Efficient Electro‐reforming of 5‐Hydroxymethylfurfural on Vertically Oriented Nickel Nanosheet/Carbon Hybrid Catalysts: Structure–Function Relationships

Anionic regulation Fe/NiOOH electrocatalysts to boost electrooxidation performance of biomass derived 5-hydroxymethylfurfural

Nickel-based catalysts show great potential as promising candidates for the electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF). However, the limited adsorption capacity of nickel-based catalysts for OH- and HMF limits their further development. In this study, amorphous Fe/NiOOH-SOx was generated from nanosheets (Fe/NiOOH-Ni3S2), which was pre-fabricated on nickel foam via pre-reconstruction and anionic regulation strategy. The optimized catalyst Fe/NiOOH-Ni3S2 demonstrated exceptional activity in the HMF oxidation reaction (HMFOR) with a current density of 10 mA cm-2 at 1.32 V vs RHE, accompanying with the 98.9 % HMF conversion, 97.8 % 2,5-Furandicarboxylic acid (FDCA) selectivity, 96.8 % Faraday efficiency, and stability for ten cycles. The incorporating amorphous FeOOH reduces the electron density around Ni, promoting the formation of high-valent Ni spices. Meanwhile, the SOx combined with amorphous hydroxy nickel oxide provides unsaturated sites, which enhances the adsorption capacity of HMF. Density functional theory (DFT) computations reveal that the designed amorphous Fe/NiOOH and surface-adsorbed SOx collectively modulate the electronic structure of the catalyst, causing an upwards shift of the NiOOH d-band center and enhancing adsorption capacities for both HMF and OH-. This study proposes the adsorption enhancement mechanism of regulating electronic structure and offers a rational strategy for HMFOR electrocatalysts.

Integrated electrochemical and chemical system for ampere-level production of terephthalic acid alternatives and hydrogen

2,5-Furandicarboxylic acid (FDCA), a critical polymer platform molecule that can potentially replace terephthalic acid, coupled hydrogen coproduction holds great prospects via electrolysis. However, the electrosynthesis of FDCA faces challenges in product separation from complex electrolytes and unclear electrochemical and nonelectrochemical reactions during the 5-hydroxymethylfurfural (HMF) oxidation. Herein, an electrochemical/chemical integrated system of alkaline HMF-H2O co-electrolysis is proposed, achieving distillation-free synthesis of high-purity FDCA by acidic separation/purification and hydrogen coproduction. This system achieves ampere-level current densities of 812 and 1290 mA cm-2 at potentials of 1.50 and 1.60 V, with nearly 100% FDCA yield and HMF conversion in only 6 min at 1.50 V. The electrooxidation of HMF involves a coupling of electrochemical and nonelectrochemical reactions, wherein the aldehyde group is dehydrogenated and oxidized, followed by dehydrated and oxidized of the hydroxyl group, ultimately forming FDCA. Concurrently, nonelectrochemical reactions of intermolecular electron transfer occur in HMF and aldehyde group-containing intermediates.

Strong p-d Orbital Hybridization on Bismuth Nanosheets for High Performing CO2 Electroreduction

Single-atom alloys (SAAs) show great potential for a variety of electrocatalytic reactions. However, the atomic orbital hybridization effect of SAAs on the electrochemical reactions is unclear yet. Herein, the in situ confinement of vanadium/molybdenum/tungsten atoms on bismuth nanosheet is shown to create SAAs with rich grain boundaries, respectively. With the detailed analysis of microstructure and composition, the strong p-d orbital hybridization between bismuth and vanadium enables the exceptional electrocatalytic performance for carbon dioxide (CO2 ) reduction with the Faradaic efficiency nearly 100% for C1 products in a wide potential range from -0.6 to -1.4 V, and a long-term electrolysis stability for 90 h. In-depth in situ investigations with theoretical computations reveal that the electron delocalization toward vanadium atoms via the p-d orbital hybridization evokes the bismuth active centers for efficient CO2 activation via the σ-donation of O-to-Bi, thus reduces protonation energy barriers for formate production. With such fundamental understanding, SAA electrocatalyst is employed to fabricated the solar-driven electrolytic cell of CO2 reduction and 5-hydroxymethylfurfural oxidation, achieving an outstanding 2,5-furandicarboxylic acid yield of 90.5%. This study demonstrates a feasible strategy to rationally design advanced SAA electrocatalysts via the basic principles of p-d orbital hybridization.

Controllable evolution of NiOOH/Au3+ active species for the oxidation of 5-hydroxymethylfurfural

To induce the generation of active species at the metal-carrier interface, a new synthetic strategy was successfully developed to reconstruct the Ni MOF-Au via electrochemical activation. This unique configuration not only obtained high-valence NiOOH-Au3+ species, but also stably anchored the Au nanoparticles on the surface of the catalyst. As a result, nearly 99.8% FDCA yield and 100% Faraday efficiency of FDCA were achieved at the optimal potential of 1.57 V vs. RHE. Therefore, this electrochemical reconstruction provides new insights for the development of efficient catalysts in other heterogeneous catalytic reactions.

Bionic Mineralization toward Scalable MOF Films for Ampere-Level Biomass Upgrading

With significant advances in metal-organic framework (MOF) nanostructure preparation, however, the facile synthesis of large-scale MOF films with precise control of the interface structure and surface chemistry is still challenging to achieve with satisfactory performance. Herein, we introduce a universal strategy bridging metal corrosion chemistry and bionic mineralization to synthesize 16 MOF films on 7 metal supports under ambient conditions. The robustness to explore unlimited libraries of MOF films (e.g., carboxylate-, N-heterocycle-, phenolic-, and phosphonate-MOFs) on supports is evoked by independently regulating the metal redox behavior, electrolyte properties, and organic ligands along with hydrogen evolution or oxygen reduction, which offers the basic guidelines for regulating the microstructure and composition of MOFs on the Pourbaix diagram. In conjunction with multiple manufacturing methods, we demonstrated proof of concept for "printing" a large variety of MOF patterns from micrometer to meter scales. Furthermore, a large-area electrolyzer (64 cm2) devised enables 5-hydroxymethylfurfural oxidation to achieve a record-breaking current of 3.0 A at 1.63 V with 2,5-furandicarboxylic acid production, leading to the simultaneous production of H2 gas and valuable feedstocks. The improved electrocatalytic activity for significantly boosting the 5-hydroxymethylfurfural oxidation exemplifies one of the functional MOF films for given applications beyond biomass upgrading.

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.

A Liquid-Liquid-Solid System to Manipulate the Cascade Reaction for Highly Selective Electrosynthesis of Aldehyde

Electrocatalytic synthesis of aldehydes from alcohols exhibits unique superiorities as a promising technology, in which cascade reactions are involved. However, the cascade reactions are severely limited by the low selectivity resulting from the peroxidation of aldehydes in a traditional liquid-solid system. Herein, we report a novel liquid-liquid-solid system to regulate the selectivity of benzyl alcohol electrooxidation. The selectivity of benzaldehyde increases 200-fold from 0.4 % to 80.4 % compared with the liquid-solid system at a high current density of 136 mA cm^-2 , which is the highest one up to date. In the tri-phase system, the benzaldehyde peroxidation is suppressed efficiently, with the conversion of benzaldehyde being decreased from 87.6 % to 3.8 %. The as-produced benzaldehyde can be in situ extracted to toluene phase and separated from the electrolyte to get purified benzaldehyde. This strategy provides an efficient way to efficiently enhance the selectivity of electrocatalytic cascade reactions.

Upgrading Organic Compounds through the Coupling of Electrooxidation with Hydrogen Evolution

The electrocatalytic splitting of water is recognized to be the most sustainable and clean technology for the production of hydrogen (H2 ). Unfortunately, the efficiency is seriously restricted by the sluggish kinetics of the oxygen evolution reaction (OER) at the anode. In contrast to the OER, the electrooxidation of organic compounds (EOO) is more thermodynamically and kinetically favorable. Thus, the coupling of the EOO and hydrogen evolution reaction (HER) has emerged as an alternative route, as it can greatly improve the catalytic efficiency for the production of H2 . Simultaneously, value-added organic compounds can be generated on the anode through electrooxidation upgrading. In this Minireview, we highlight the latest progress and milestones in coupling the EOO with the HER. Emphasis is focused on the design of the anode catalyst, understanding the reaction mechanism, and the construction of the electrolyzer. Moreover, challenges and prospects are offered relating to the future development of this emerging technology.

Selective Electrooxidation of Biomass-Derived Alcohols to Aldehydes in a Neutral Medium: Promoted Water Dissociation over a Nickel-Oxide-Supported Ruthenium Single-Atom Catalyst

The biomass-derived alcohol oxidation reaction (BDAOR) holds great promise for sustainable production of chemicals. However, selective electrooxidation of alcohols to value-added aldehyde compounds is still challenging. Herein, we report the electrocatalytic BDAORs to selectively produce aldehydes using single-atom ruthenium on nickel oxide (Ru₁ -NiO) as a catalyst in the neutral medium. For electrooxidation of 5-hydroxymethylfurfural (HMF), Ru₁ -NiO exhibits a low potential of 1.283 V at 10 mA cm^-2 , and an optimal 2,5-diformylfuran (DFF) selectivity of 90 %. Experimental studies reveal that the neutral electrolyte plays a critical role in achieving a high aldehyde selectivity, and the single-atom Ru boosts HMF oxidation in the neutral medium by promoting water dissociation to afford OH*. Furthermore, Ru₁ -NiO can be extended to selective electrooxidation of a series of biomass-derived alcohols to corresponding aldehydes, which are conventionally difficult to obtain in the alkaline medium.