电化学合成耦合可再生能源制氢:机遇与挑战

利用可再生能源实现物质和能量的转化,是发展节能减排技术、实现双碳目标的重要手段.有机电合成是一种温和、清洁、高效的物质合成方法,可以有效解决传统化工过程的高能耗和高污染问题.将电解水制氢与有机电合成耦合,利用水分解产生的活性氧/氢直接氧化/还原有机物,不仅有助于降低能耗,还可以生产高附加值有机化工产品,是提高电能利用效率、降低生产成本的有效方案.然而,尽管这种方法具有诸多优势,其工业化应用仍面临一系列难题.本文回顾了电化学合成的发展历史,探讨了氢能时代为电化学合成带来的发展机遇.同时,分析了将电化学合成与电解水耦合所面临的挑战以及未来发展方向.首先,应当慎重选择与电解水制氢耦合的阳极反应体系,其氧化产物不但要具有比反应物更高的经济价值,而且要有较大的市场需求量,以匹配制氢规模.其次,虽然在热力学上有机物氧化比析氧更容易发生,但在动力学及传质方面,有机物氧化可能存在劣势,因此必须开发适用于工业制氢电流密度(500‒2000 mA cm^(‒2))的有机物氧化电极材料.第三,阳极有机产物选择性不仅影响反应物的利用率,而且决定后续分离纯化成本,需要通过调控活性氢/氧及有机物表面的竞争吸附等手段,提高阳极目标产物选择性及法拉第效率.第四,隔膜是分离两极反应物料、防止副反应发生的重要部件.然而,现有的阴、氧离子交换膜的耐有机物腐蚀性能差,需要开发适用于电解耦合体系的、具有高离子传导能力且性能稳定的新型隔膜材料.最后,当有机物氧化与电解水耦合后,产物的分离复杂程度增加,需要将精馏、萃取、膜分离等手段与电化学反应相结合,以提升电解过程效率.综上,本文讨论了电化学合成耦合可再生能源制氢的若干技术难题,为未来电合成与氢能技术共同发展提供新思路.

Efficient light-driven reductive amination of furfural to furfurylamine over ruthenium-cluster catalyst

Selective reductive amination of carbonyl compounds with high activity is very essential for the chemical and pharmaceutical industry,but scarcely successful paradigm was reported via efficient photocatalytic reactions.Herein,the ultrasmall Ru nanoclusters(~0.9 nm)were successfully fabricated over P25 support with positive charged Ru^(δ+)species at the interface.A new route was developed to achieve the furfural(FAL)to furfurylamine(FAM)by coupling the light-driven reductive amination and hydrogen transfer of ethanol over this type catalyst.Strikingly,the photocatalytic activity and selectivity are strongly dependent on the particle size and electronic structure of Ruthenium.The Ru^(δ+)species at the interface promote the formation of active imine intermediates;moreover,the Ru nanoclusters facilitate the separation efficiency of electrons and holes as well as accelerate the further hydrogenation of imine intermediates to product primary amines.In contrast Ru particles in larger nanometer size facilitate the formation of the furfuryl alcohol and excessive hydrogenation products.In addition,the coupling byproducts can be effectively inhibited via the construction of sub-nanocluster.This study offers a new path to produce the primary amines from biomass-derived carbonyl compounds over hybrid semiconductor/metal-clusters photocatalyst via light-driven tandem catalytic process.

Electro-oxidation of 5-hydroxymethylfurfural in a low-concentrated alkaline electrolyte by enhancing hydroxyl adsorption over a single-atom supported catalyst

Electrocatalytic oxidation of 5-hydroxymethylfurfural(HMF)to 2,5-furandicarboxylic acid(FDCA),a sustainable strategy to produce bio-based plastic monomer,is always conducted in a high-concentration alkaline solution(1.0 mol L^(-1)KOH)for high activity.However,such high concentration of alkali poses challenges including HMF degradation and high operation costs associated with product separation.Herein,we report a single-atom-ruthenium supported on Co3O4(Ru1-Co3O4)as a catalyst that works efficiently in a low-concentration alkaline electrolyte(0.1 mol L^(-1)KOH),exhibiting a low potential of 1.191 V versus a reversible hydrogen electrode to achieve 10 m A cm^(-2)in 0.1 mol L^(-1)KOH,which outperforms previous catalysts.Electrochemical studies demonstrate that single-atom-Ru significantly enhances hydroxyl(OH-)adsorption with insufficient OH-supply,thus improving HMF oxidation.To showcase the potential of Ru1-Co3O4catalyst,we demonstrate its high efficiency in a flow reactor under industrially relevant conditions.Eventually,techno-economic analysis shows that substitution of the conventional1.0 mol L^(-1)KOH with 0.1 mol L^(-1)KOH electrolyte may significantly reduce the minimum selling price of FDCA by 21.0%.This work demonstrates an efficient catalyst design for electrooxidation of biomass working without using strong alkaline electrolyte that may contribute to more economic biomass electro-valorization.

Metal vacancy-enriched layered double hydroxide for biomass molecule electrooxidation coupled with hydrogen production

The electrochemical oxidation of biomass molecules coupling with hydrogen production is a promising strategy to obtain both green energy and value-added chemicals;however,this strategy is limited by the competing oxygen evolution reactions and high energy consumption.Herein,we report a hierarchical CoNi layered double hydroxides(LDHs)electrocatalyst with abundant Ni vacancies for the efficient anodic oxidation of 5-hydroxymethylfurfural(HMF)and cathodic hydrogen evolution.The unique hierarchical nanosheet structure and Ni vacancies provide outstanding activity and selectivity toward several biomass molecules because of the finely regulated electronic structure and highly-exposed active sites.In particular,a high faradaic efficiency(FE)at a high current density(99%at 100 mA cm^(-2))is achieved for HMF oxidation,and a two-electrode electrolyzer is assembled based on the Ni vacancies-enriched LDH,which realized a continuous synthesis of highly-pure 2,5-furandicarboxylic acid products with high yields(95%)and FE(90%).

Recent Progress in Electrocatalytic Conversion of Lignin:From Monomers,Dimers,to Raw Lignin

Lignin,as the second largest renewable biomass resource in nature,has increasingly received significant interest for its potential to be transformed into valuable chemicals,potentially contributing to carbon neutrality.Among different approaches,renewable electricity-driven biomass conversion holds great promise to substitute a petroleum resource-driven one,owing to its characteristics of environmental friendliness,high energy efficiency,and tunable reactivity.The challenges lie on the polymeric structure and complex functional groups in lignin,requiring the development of efficient electrocatalysts for lignin valorization with enhanced activity and selectivity toward targeted chemicals.In this Review,we focus on the advancement of electrocatalytic valorization of lignin,from monomers,to dimers and to raw lignin,toward various valueadded chemicals,with emphasis on catalyst design,reaction innovation,and mechanistic study.The general strategies for catalyst design are also summarized,offering insights into enhancing the activity and selectivity.Finally,challenges and perspectives for the electrocatalytic conversion of lignin are proposed.

Janus electrode with simultaneous management on gas and liquid transport for boosting oxygen reduction reaction

Oxygen reduction efficiency holds the key for renewable energy technologies including fuel cells and metal-air batteries,which involves coupling diffusion-reaction-conduction processes at the interface of catalyst/electrolyte,and thus rational electrode design facilitating mass transportation stands as a key issue for fast oxygen reduction reaction(ORR).Herein,we report a Janus electrode with asymmetric wettability prepared by partly modifying aerophobic nitrogen doped carbon nanotube arrays with polytetrafluoroethylene(PTFE)as a high performance catalytic electrode for ORR.The Janus electrode with opposite wettability on adjacent sides maintains stable gas reservoir in the aerophilic side while shortening O2 pathway to catalysts in the aerophobic side,resulting in superior ORR performance(22.5 mA/cm^2@0.5 V)than merely aerophilic or aerophilic electrodes.The Janus electrode endows catalytic performance even comparable to commercial,Pt/C in the alkali ne electrolyte,exploiting a previously unrecognized opport unity that guides electrode design for the gas-consumption electrocatalysis.

Recent advances in non-noble electrocatalysts for oxidative valorization of biomass derivatives

Electrocatalysis is deemed as a promising approach for sustainable energy conversion and chemical production.Although a variety of cathode reactions(e.g.,hydrogen evolution and CO_(2)/N_(2)reduction)produce valuable fuels and chemicals,the extensively studied oxygen evolution reaction(OER)at anode only generates O_(2),which is not a high-value product.Substituting the OER with thermodynamically more favorable biomass derivative oxidation reactions(BDORs)not only enables energy-saving electrocatalysis,but also provides value-added anode products.Recent achievements have demonstrated that non-noble electrocatalysts are promising for BDORs.Herein,we provide a comprehensive review on recent achievements in the field of electrochemical BDORs catalyzed by non-noble catalysts.We start by summarizing the electrocatalytic oxidation of different types of biomass-derived substrates,aiming to show the advantages of the electrocatalytic pathway and to introduce the state-of-the-art non-noble catalysts.The reaction mechanisms of non-noble-material-catalyzed BDORs are then summarized and classified into three types according to the acceptor of hydrogen species during the dehydrogenation of biomass derivatives.Subsequently,discussions are devoted to the strategies for promoting the performances of non-noble electrocatalysts.Finally,we propose our opinions regarding future trends and major challenges in this field.

An Electrocatalytic Strategy for Dehydrogenative[4+2]Cycloaddition over a Cobalt-Based Catalyst

Exploring the anodic reaction to substitute conventional oxygen evolution reaction(OER)for the synthesis of complex pharmaceutical molecules is highly attractive.Here,we report an electrocatalytic strategy for dehydrogenative[4+2]cycloaddition of N,N-dialkylanilines with maleimides via dual functionalization of both C(sp3)-H and C(sp2)-H bonds,by using an electrochemically activated cobalt carbonate hydroxide hydrate supported on carbon cloth(CCHH-A/CC),affording various tetrahydroquinolines with high yields.This electrochemical transformation proceeds with high activity and stability,as well as good substrate compatibility.Mechanism study shows thatα-aminoalkyl radical exists in the electrooxidation reaction.This strategy shows significant potential for the synthesis of valuable chemicals by using an electrocatalytic strategy.

A nickel-iron layered double hydroxide-supported Au catalyst for efficient electrocatalytic C-C coupling reaction coupled with H_(2) production

Coupling of cathodic H_(2) production with electrosynthesis of organic compounds not only solves the problem of sluggish oxygen evolution reaction(OER) kinetics, but also produces valuable chemicals. However, this strategy has rarely been explored for direct and selective C(sp~3)-H activation to construct C-C bonds, which could significantly enhance the synthetic efficiency in organic synthesis. Here, we report a nickel-iron layered double hydroxide-supported gold catalyst(Au/NiFe-LDH) for efficient electrocatalytic C-C coupling reaction in direct C(sp~3)-H alkynylation of tertiary aliphatic amines with 1-iodoalkynes, which is coupled with H_(2) production. Specifically, triethylamine and 1-iodoalkynes undergo efficient alkynylation to afford propargylamine in high yield(79%) and recycling ability without addition of external oxidants, coupling with 78-fold higher H_(2) productivity compared with water splitting under the same potential. This work may shed light on OER-substituted reaction towards C-C bond formation reactions under mild conditions.