少层氮化碳光催化剂合成太阳燃料和高附加值化学品:现状与展望

将太阳能直接转化为燃料和高附加值化学品是存储可再生能源非常有前景的策略.少层氮化碳材料因其比表面积大、电荷传输距离短、活性位点暴露多等优点,在合成太阳燃料和高附加值化学品方面展示出巨大潜力,而成为光催化领域的研究热点.本文总结了近年来少层氮化碳基光催化剂的合成、结构调控及其在合成太阳燃料和高附加值化学品领域的研究成果.首先简要介绍了用于少层氮化碳材料的合成方法,包括剥离、热氧化刻蚀、真空冷冻干燥、分子自组装、球磨以及化学气相沉积技术,并讨论了不同方法的优缺点.其次,深入分析了少层氮化碳的化学改性(杂原子掺杂、缺陷工程、异质结构)、微结构调控(零维量子点、一维纳米带、二维纳米网片、三维纳米组装体)对其电子结构、光学性质、电荷分离和迁移的影响.针对不同的改性策略,分别从光催化反应三个过程(光的捕集、光生电荷分离和迁移及表面催化反应)讨论其对于少层氮化碳基材光催化活性的促进作用以及存在的不足,涉及的反应包括光催化分解水、CO_(2)还原、氮气还原合成氨、光合成过氧化氢和光催化有机小分子合成.最后,从光催化剂设计、光催化反应体系、反应机理和反应器四个方面讨论了少层氮化碳基光催化剂在合成太阳燃料和高附加值化学品领域面临的挑战和发展前景.对于催化剂设计,其表面态决定光催化性能.目前定量研究催化剂表面缺陷和光催化活性之间的关系是一个巨大的挑战,未来在精确控制少层氮化碳基光催化剂的表面态方面需要更多的研究工作;另外,目前报道的助催化剂大多是大颗粒或者纳米粒子,未来应将具有高活性的单原子或单活性位点与少层氮化碳结合,以提高其光催化活性.对于光催化反应体系,目前报道的研究工作大部分需要利用使用牺牲剂消耗掉空穴,以实现高效分解水产氢、CO_(2)还原、合成氨,从而导致成本较高.将原本消耗牺牲剂端的氧化半反应替换为附加值更高的化学品同时产氢、CO_(2)还原或者N2还原则可以充分利用光生电子和空穴,减少浪费.目前报道的大部分反应机理和反应路径依赖于假设,缺少确凿的证据,可以利用先进的原位技术如时间分辨光谱、瞬态和稳态光谱应该用来研究少层氮化碳的激发态载流子动力学和反应中间物种,进而阐明反应路径.对于反应器,目前反应采用的都是罐子反应器,但存在传质受限和催化剂分离与回收成本问题,结合工业化需求,未来可开发流动反应器来解决上述问题.此外,大数据、机器学习、人工智能对于繁琐的催化剂筛选以及预测提供了快捷路径,这将是未来的研究重点.

Tuning Structures and Microenvironments of Cu-Based Catalysts for Sustainable CO_(2) and CO Electroreduction

CONSPECTUS:The carbon balance has been disrupted by the widespread use of fossil fuels and subsequent excessive emissions of carbon dioxide(CO_(2)),which has become an increasingly critical environmental challenge for human society.The production and use of renewable energy sources and/or chemicals have been proposed as important strategies to reduce emissions,of which the electrochemical CO_(2)(or CO)reduction reaction(CO_(2)RR/CORR)in the aqueous systems represents a promising approach.Benefitted by the capacity of manufacturing high-value-added products(e.g.,ethylene,ethanol,formic acid,etc.)with a net-zero carbon emission,copper-based CO_(2)RR/CORR powered by sustainable electricity is regarded as a potential candidate for carbon neutrality.However,the diversity of selectivities in copper-based systems poses a great challenge to the research in this field and sets a great obstacle for future industrialization.To date,scientists have revealed that the electrocatalyst design and preparation play a significant role in achieving efficient and selective CO_(2)-to-chemical(or CO-to-chemical)conversion.Although substantial efforts have been dedicated to the catalyst preparation and corresponding electrosynthesis of sustainable chemicals from CO_(2)/CO so far,most of them are still derived from empirical or random searches,which are relatively inefficient and cost-intensive.Most of the mechanism studies have suggested that both intrinsic properties(such as electron states)and extrinsic environmental factors(such as surface energy)of a catalyst can significantly alter catalytic performance.Thus,these two topics are mainly discussed for copper-based catalyst developments in this Account.Here,we provided a concise and comprehensive introduction to the well-established strategies employed for the design of copperbased electrocatalysts for CO_(2)RR/CORR.We used several examples from our research group,as well as representative studies of other research groups in this field during the recent five years,with the perspectives of tuning local electron states,regulating alloy phases,modifying interfacial coverages,and adjusting other interfacial microenvironments(e.g.,molecule modification or surface energy).Finally,we employed the techno-economic assessment with a viewpoint on the future application of CO_(2)/CO electroreduction in manufacturing sustainable chemicals.Our study indicates that when carbon price is taken into account,the electrocatalytic CO_(2)-to-chemical conversion can be more market-competitive,and several potential value-added products including formate,methanol,ethylene,and ethanol can all make profits under optimal operating conditions.Moreover,a downstream module employing traditional chemical industrial processes(e.g.,thermal polymerization,catalytic hydrolysis,or condensation process)will also make the whole electrolysis system profitable in the future.These design principles,combined with the recent advances in the development of efficient copper-based electrocatalysts,may provide a low-cost and long-lasting catalytic system for a profitable industrial-scale CO_(2)RR in the future.

Enhanced N-doping in mesoporous carbon for efficient electrocatalytic CO2 conversion

The capability of electrocatalytic reducti on of carbon dioxide(CO2)using nitrogen(N)-doped carb on strongly depe nds on the N-dopi ng level and their types.In this work,we developed a strategy to generate mesoporous N-doped carb on frameworks with tun able configurati ons and contents of N dopants,by using a secondary doping process via the treatment of N,N-dimethylformamide(DMF)solvent.The obtained mesoporous N-doped carbon(denoted as MNC-D)served as an efficient electrocatalyst for electroreduction of CO2 to CO.A high Faradaic efficiency of^92%and a partial current density for CO of-6.8 mA·cm^-2 were achieved at a potential of-0.58 V vs.RHE.Electrochemical analyses further revealed that the active sites within the N-doped carb on catalysts were the pyridinic N and defects gen erated by the DMF treatme nt,which enhan ced the activati on and adsorpti on CO2 molecules.Our study suggests a new approach to develop efficie nt carb on-based catalysts for potential scalable CO2 reduction reaction(CO2RR)to fuels and chemicals.

Aqueous electrocatalytic N2 reduction under ambient conditions

Recently, the electrochemical N2 reduction reaction （NRR） in aqueous electrolytes at ambient temperature and pressure has demonstrated its unique advantages and potentials. The reactants are directly derived from gaseous N2 and water, which are naturally abundant, and NH3 production is important for fertilizers and other industrial applications. To improve the conversion yield and selectivity （mainly competing with water reduction）, electrocatalysts must be rationally designed to optimize the mass transport, chemisorption, and transduction pathways of protons and electrons. In this review, we summarize recent progress in the electrochemical NRR. Studies of electrocatalyst designs are summarized for different categories, including metal-based catalysts, metal oxide-derived catalysts, and hybrid catalysts. Strategies for enhancing the NRR performance based on the facet orientation, metal oxide interface, crystallinity, and nitrogen vacancies are presented. Additional system designs, such as lithium-nitrogen batteries, and the solvent effect are introduced. Finally, existing challenges and prospects are discussed.

Pushing the activity of CO2 electroreduction by system engineering

As a promising technology that may solve global environmental challenges and enable intermittent renewable energy storage as well as zero-carbon-emission energy cycling, the carbon dioxide reduction reaction has been extensively studied in the past several years. Beyond the fruitful progresses and innovations in catalysts, the system engineering-based research on the full carbon dioxide reduction reaction is urgently needed toward the industrial application. In this review, we summarize and discuss recent works on the innovations in the reactor architectures and optimizations based on system engineering in carbon dioxide reduction reaction. Some challenges and future trends in this field are further discussed, especially on the system engineering factors.

Atomic layer deposition-induced integration of N-doped carbon particles on carbon foam for flexible supercapacitor

Flexible devices have attracted abundant attention in energy storage systems.In this paper,we presented a novel approach for fabricating flexible supercapacitor based on metal organic frameworks-derived material.In this approach,a uniform zeolitic imidazolate frameworks-8 layer with a high mass loading was deposited on a flexible carbon foam(CF)skeleton efficiently by the induction of a uniform ZnO nanomembrane prepared via an atomic layer deposition technique.A flexible N-doped carbon particle-carbon foam(N-CP-CF)composite with a hierarchically porous structure and a large specific surface area(i.e.,538 m^(2) g^(-1))was obtained in a subsequent pyrolysis process.The resultant materials have the excellent electrochemical performance(i.e.,a high specific capacitance of 300 F g^(-1) and a high energy density of 20.8 W h kg^(-1)).The N-CP-CF composite can provide a stable capacitance(i.e.,250 F g^(-1))and an energy density(i.e.,17.36 W h kg^(-1))under large deformation(25% of original thickness).This work could propose a promising strategy in fabrication of flexible electrode with a large potential towards energy storage applications in the future.

2020 Roadmap on gas-involved photo-and electro-catalysis

Green reactions not only provide us chemical products without any pollution,but also offer us the viable technology to realize difficult tasks in normal conditions.Photo-,photoelectro-,and electrocatalytic reactions are indeed powerful tools to help us to embrace bright future.Especially,some gas-involved reactions are extremely useful to change our life environments from energy systems to liquid fuels and cost-effective products,such as H2 evolution(H2 production),02 evolution/reduction,CO2 reduction,N2 reduction(or N2 fixation) reactions.We can provide fuel cells clean H2 for electric vehicles from H2 evolution reaction(HER),at the same time,we also need highly efficient 02 reduction reaction(ORR) in fuel cells for improving the reaction kinetics.Moreover,we can get the clean oxidant O2 from water through O2 evolution reaction(OER),and carry out some reactions without posing any pollution to reaction systems.Furthermore,we can translate the greenhouse gas CO2 into useful liquid fuels through CO2 reduction reaction(CRR).Last but not the least,we can get ammonia from N2 reduction reaction(NRR),which can decrease energy input compared to the traditional Hubble process.These reactions,such as HER,ORR,OER,CRR and NRR could be realized through solar-,photoelectro-and electro-assisted ways.For them,the catalysts used play crucial roles in determining the efficiency and kinds of products,so we should consider the efficiency of catalysts.However,the cost,synthetic methods of catalysts should also be considered.Nowadays,significant progress has been achieved,however,many challenges still exist,reaction systems,catalysts underlying mechanisms,and so on.As extremely active fields,we should pay attention to them.Under the background,it has motivated us to contribute with a roadmap on ’GasInvolved Photo-and Electro-Catalysis’.

Atomically-dispersed catalyst by solid-liquid phase transition for CO_(2)electroreduction

The electrochemical reduction of carbon dioxide(CO_(2))to value-added fuels and chemicals provides a promising way to realize sustainable carbon recycling[1].Developing robust electrocatalysts with high activity and selectivity is critically important for efficient electrochemical CO_(2)reduction reaction(CO_(2)RR).Generally,it is challenging to achieve high efficiency and selectivity simultaneously in the CO_(2)RR due to the multi-proton/electron transfer processes and complex reaction intermediates.