Identification of Dynamic Active Sites Among Cu Species Derived from MOFs@CuPc for Electrocatalytic Nitrate Reduction Reaction to Ammonia

Direct electrochemical nitrate reduction reaction(NITRR)is a promising strategy to alleviate the unbalanced nitrogen cycle while achieving the electrosynthesis of ammonia.However,the restructuration of the high-activity Cu-based electrocatalysts in the NITRR process has hindered the identification of dynamical active sites and in-depth investigation of the catalytic mechanism.Herein,Cu species(single-atom,clusters,and nanoparticles)with tunable loading supported on N-doped TiO_(2)/C are successfully manufactured with MOFs@CuPc precursors via the pre-anchor and post-pyrolysis strategy.Restructuration behavior among Cu species is co-dependent on the Cu loading and reaction potential,as evidenced by the advanced operando X-ray absorption spectroscopy,and there exists an incompletely reversible transformation of the restructured structure to the initial state.Notably,restructured CuN_(4)&Cu_(4) deliver the high NH_(3) yield of 88.2 mmol h^(−1)g_(cata)^(−1) and FE(~94.3%)at−0.75 V,resulting from the optimal adsorption of NO_(3)^(−) as well as the rapid conversion of^(*)NH_(2)OH to^(*)NH_(2) intermediates originated from the modulation of charge distribution and d-band center for Cu site.This work not only uncovers CuN_(4)&Cu_(4) have the promising NITRR but also identifies the dynamic Cu species active sites that play a critical role in the efficient electrocatalytic reduction in nitrate to ammonia.

Elucidating the Role of Mass Transfer in Electrochemical Redox Reactions on Electrospun Fibers

Mass transfer can tune the surface concentration of reactants and products and subsequently infl uence the catalytic perfor-mance.The morphology of nanomaterials plays an important role in the mass transfer of reaction microdomains,but related studies are lacking.Herein,a facile electrospinning technique utilizing cellulose was employed to fabricate a series of carbon nanofi bers with diff erent diameters,which exhibited excellent electrochemical nitrate reduction reaction and oxygen evolu-tion reaction activities.Furthermore,the microstructure of electrocatalysts could infl uence the gas-liquid-solid interfacial mass transfer,resulting in diff erent electrochemical performances.

Oxygen‑Coordinated Single Mn Sites for Efficient Electrocatalytic Nitrate Reduction to Ammonia

Electrocatalytic nitrate reduction reaction has attracted increasing attention due to its goal of low carbon emission and environmental protection.Here,we report an efficient NitRR catalyst composed of single Mn sites with atomically dispersed oxygen(O)coordination on bacterial cellulose-converted graphitic carbon(Mn-O-C).Evidence of the atomically dispersed Mn-(O-C_(2))_(4)moieties embedding in the exposed basal plane of carbon surface is confirmed by X-ray absorption spectroscopy.As a result,the as-synthesized Mn-O-C catalyst exhibits superior NitRR activity with an NH_(3)yield rate(RNH_(3))of 1476.9±62.6μg h^(−1)cm^(−2)at−0.7 V(vs.reversible hydrogen electrode,RHE)and a faradaic efficiency(FE)of 89.0±3.8%at−0.5 V(vs.RHE)under ambient conditions.Further,when evaluated with a practical flow cell,Mn-O-C shows a high RNH_(3)of 3706.7±552.0μg h^(−1)cm^(−2)at a current density of 100 mA cm−2,2.5 times of that in the H cell.The in situ FT-IR and Raman spectroscopic studies combined with theoretical calculations indicate that the Mn-(O-C_(2))_(4)sites not only effectively inhibit the competitive hydrogen evolution reaction,but also greatly promote the adsorption and activation of nitrate(NO_(3)^(−)),thus boosting both the FE and selectivity of NH_(3)over Mn-(O-C_(2))_(4)sites.

Nanoengineering Metal–Organic Frameworks and Derivatives for Electrosynthesis of Ammonia

Electrocatalytic synthesis under mild conditions has become increasingly important as one of the practical alternatives for industrial applications,especially for the green ammonia(NH_(3))industry.A properly engineered electrocatalyst plays a vital role in the realization of superior catalytic performance.Among various types of promising nanomaterials,metal–organic frameworks(MOFs)are competitive candidates for developing efficient electrocatalytic NH_(3) synthesis from simple nitrogen-containing molecules or ions,such as N_(2) and NO_(3)^(−).In this review,recent advances in the development of electrocatalysts derived from MOFs for the electrosynthesis of NH_(3) are collected,categorized,and discussed,including their application in the N_(2) reduction reaction(NRR)and the NO_(3)^(−)reduction reaction(NO3RR).Firstly,the fundamental principles are illustrated,such as plausible mechanisms of NH_(3) generation from N_(2) and NO_(3)^(−),the apparatus of corresponding electrocatalysis,parameters for evaluation of reaction efficiency,and detection methods of yielding NH_(3).Then,the electrocatalysts for NRR processes are discussed in detail,including pristine MOFs,MOF-hybrids,MOF-derived N-doped porous carbons,single atomic catalysts from pyrolysis of MOFs,and other MOF-related materials.Subsequently,MOF-related NO3RR processes are also listed and discussed.Finally,the existing challenges and prospects for the rational design and fabrication of electrocatalysts from MOFs for electrochemical NH_(3) synthesis are presented,such as the evolution of investigation methods with artificial intelligence,innovation in synthetic methods of MOF-related catalysts,advancement of characterization techniques,and extended electrocatalytic reactions.

High-throughput mechanistic study of highly selective hydrogen-bonded organic frameworks for electrochemical nitrate reduction to ammonia

Hydrogen-bonded organic frameworks(HOFs),an emerging porous macrocyclic materials linked by hydrogen-bond,hold potential for gas separation and storage,sensors,optical,and electrocatalysts.Here,HOF-based electrocatalysts are rationally developed for nitrates reduction to ammonia,allowing not only to regulate wastewater pollution but also to accomplish carbon-neutral ammonia(NH_(3))synthesis.We preform high-throughput computational screening of thirty-six HOFs with various metals as active sites,denoted as HOF-M1,for nitrate reduction reaction(NO_(3)RR)toward NH_(3).We have implemented a hierarchical four-step screening strategy,and ultimately,HOF-Ti1 was selected based on its exceptional catalytic activity and selectivity in the NO_(3)RR process.Through additional analysis,we discovered that the d band center of the active metal sites serves as an effective parameter for designing and predicting the performance of HOFs in NO_(3)RR.This research not only showcases the immense potential of electrocatalysis in transforming NO_(3)RR into NH_(3)but also provides researchers with a compelling incentive to undertake further experimental investigations.

Zeolite-mediated hybrid Cu^(+)/Cu~0 interface for electrochemical nitrate reduction to ammonia

The electrocatalytic conversion of reactive nitrogen species to ammonia is a promising strategy for efficient NH_(3) synthesis.In this study,we reveal that the hybrid Cu^(+)/Cu~0 interface is catalytically active for electrochemical ammonia synthesis from nitrate reduction.To maintain the hybrid Cu^(+)/Cu~0 state at negative reaction potentials,hydrophilic zeolite is used to modify Cu/Cu_(2)O electrocatalyst,which demonstrates an impressive NH_(3) production rate of 41.65 mg h^(-1) cm^(-2)with ~100% Faradaic efficiency of ammonia synthesis at-0.6 V vs.RHE.In-situ Raman spectroscopy unveil the high activity originates from the zeolite reconstruction at the electrode–electrolyte interface,which protects the valence state of Cu~0/Cu^(+) site under negative potential and promotes electrochemical activity towards NH_(3) synthesis.

Peroxynitrite Scavenging Activities of Resveratrol and Piceid

In vitro antioxidant activities of resveratrol and piceid against peroxynitrite（ONOO-） were examined by the inhibition of 3-nitrotyrosine formation.Trolox was used as a positive control.Resveratrol and piceid exhibited high ONOO--scavenging activities in a concentration dependent manner.The antioxidant activities（the concentration of test compound required to yield a 50% inhibition of tyrosine nitration,IC 50） of resveratrol and piceid against ONOO-were（48.34±0.97） and（74.69±1.49） μmol/L,respectively.Compared with that of trolox[（105.40±1.16） μmol/L],their scavenging activities were 2.2-and 1.5-fold higher for resveratrol and piceid.Formation of nitroresveratrol as shown by UV-Vis spectroscopy and liquid chromatography-tandom mass spectrometry（LC-MS/MS） analysis indicates that resveratrol could directly scavenge ONOO-via nitration reaction.Our results demonstrate that foods and medicinal herbs with resveratrol and piceid as stronger ONOO-scavengers are valuable ingredients and have healthy application in preventing humans from peroxynitrite-mediated oxidative damage by scavenging peroxynitrite efficiently.

Recent progress in electrochemical synthesis of carbon-free hydrogen carrier ammonia and ammonia fuel cells:A review

Ammonia(NH3)is a cornerstone widely used in the modern agriculture and industry,the annual global production gradually increases to almost 200 million tons.Nearly 80%of the produced NH3 is used in the fertilizer industry and is essential for the development of global agriculture and consequently for maintaining population growth.Furthermore,NH3 can power hydrogen(H2)fueled devices,such as H2 fuel cells(FC),to use the interconversion between chemical energy and electric energy of nitrogen(N2)cycle,which can effectively alleviate the intermittent problems of renewable energy.However,the problems faced by NH3 in storage and release still restrict its development.Herein,this review introduces the latest research and development of electrochemical NH3 synthesis and direct NH3 FC,as well as outlines the technical challenges,possible improvement measures and development perspectives.N2 reduction reaction(NRR)and nitrate reduction reaction(NO3RR)are two potential approaches for electrochemical NH3 synthesis.However,the existing research foundation still faces challenges in achieving high selectivity and efficiency.Direct NH3 FC are easy to transport and are expected to be widely used in mobile energy consuming equipment,but also limited by the lack of highly active and stable NH3 oxidation electrocatalysts.The perspectives of ammonia fuel cells as an alternative green energy are discussed.

The Characteristics and Genesis of the Massive Nitrate Deposits in the Turpan-Hami Basin of Xinjiang,China

Massive nitrate deposits have been discovered in the Turpan-Hami basin in northwestern China.Previously,large ore grade nitrate minerals were thought only to exist in the Atacama Desert in northern Chile.Estimates of the

Engineering transition metal-based nanomaterials for high-performance electrocatalysis

Transition metal(TM)based electrocatalysts attract increasing attention in energy conversion reactions,and current effects focus on material engineering strategies to tailor physicochemical properties of TM based electrocatalysts for improved performance.This review provides a summary about the recent advances of engineering TM based nanomaterials for electrocatalytic reactions,which include hydrogen evolution reaction(HER),oxygen evolution reaction(OER),CO2 reduction reaction(CO2RR),and nitrate reduction reaction(NO3RR).We highlight four engineering strategies,namely,size engineering,facet engineering,composition engineering,and crystal structure engineering for TM based electrocatalysts,and pay a special emphasis on exploring the relationship between their physicochemical properties and catalytic activities.We outline the opportunities in this research field,in particular,the strategy of rationally combining in-situ and operando techniques and theoretical predication to design efficient electrocatalysts.Finally,issues that deserve attention and consideration for practical applications are discussed.

Unveiling enzyme-mimetic active intermediate of a bioinspired oxo-MoS_(x) electrocatalyst for aqueous nitrate reduction

Excessive nitrate in groundwater has emerged as a serious environmental concern. The elevated nitrate concentration in drinking water causes a serious threat to public health on account of the possible transformation of nitrate to nitrite, which is one of the main predisposing factors of methemoglobinemia [1].

Au nanoclusters anchored on TiO_(2) nanosheets for high-efficiency electroreduction of nitrate to ammonia

Electrocatalytic nitrate reduction reaction(NO_(3)RR)offers a unique rationale for green NH_(3) synthesis,yet the lack of high-efficiency NO_(3)RR catalysts remains a great challenge.In this work,we show that Au nanoclusters anchored on TiO_(2) nanosheets can efficiently catalyze the conversion of NO_(3)RR-to-NH_(3) under ambient conditions,achieving a maximal Faradic efficiency of 91%,a peak yield rate of 1923μg·h^(-1)·mgcat.-1,and high durability over 10 consecutive cycles,all of which are comparable to the recently reported metrics(including transition metal and noble metal-based catalysts)and exceed those of pristine TiO_(2).Moreover,a galvanic Zn-nitrate battery using the catalyst as the cathode was proposed,which shows a power density of 3.62 mW·cm^(-2) and a yield rate of 452μg·h^(-1)·mgcat.-1.Theoretical simulations further indicate that the atomically dispersed Au clusters can promote the adsorption and activation of NO_(3)-species,and reduce the NO_(3)RR-to-NH_(3) barrier,thus leading to an accelerated cathodic reaction.This work highlights the importance of metal clusters for the NH_(3) electrosynthesis and nitrate removal.

Screening of transition metal oxides for electrocatalytic nitrate reduction to ammonia at large currents

Electrochemical nitrate reduction reaction(NO_(3)RR)towards ammonia,as an emerging and appealing technology alternative to the energy-intensive Haber-Bosch process and inefficient nitrogen reduction reaction,has recently aroused wide concern and research.However,the current research of the NO_(3)RR towards ammonia lacks the overall performance comparison of various electrocatalysts.Given this,we here make a comparison of 12 common transition metal oxide catalysts for the NO_(3)RR under a high cathodic current density of 0.25 A·cm^(-2),wherein Co_(3)O_(4) catalyst displays the highest ammonia Faradaic efficiency(85.15%)and moderate activity(ca.-0.25 V vs.reversible hydrogen electrode).Other external factors,such as nitrate concentrations in the electrolyte and applied potential ranges,have also been specifically investigated for the NO_(3)RR.

B and Fe co-doped Co_(2)P hollow nanocubes for nitrate electroreduction to ammonia

Nitrate(NO_(3)^(−))electroreduction reaction(NO_(3)^(−)RR)provides an attractive and sustainable route for NO_(3)^(−)pollution mitigation or energy-saved ammonia(NH3)synthesis.In this work,high-quality B and Fe co-doped Co_(2) P hollow nanocubes(B/Fe-Co_(2) P HNCs)are successfully synthesized though simultaneous boronation-phosphorization treatment,which reveal outstanding selectivity,activity,stability for the NO_(3)^(−)to NH_(3) conversion in neutral electrolyte because of big surface area,fast mass transport,superhydrophilic surface,and optimized electronic structure.B/Fe-Co_(2) P HNCs can achieve the high NH3 yield rate(22.67 mg h^(−1) mg_(cat)^(−1))as well as Faradaic efficiency(97.54%)for NO_(3)^(−)RR,greatly outperforming most of non-precious metal based NO_(3)^(−)RR electrocatalysts.

Electro-triggered Joule heating method to synthesize single-phase CuNi nano-alloy catalyst for efficient electrocatalytic nitrate reduction toward ammonia

Electrochemical nitrate reduction reaction(NO_(3)RR)has great potential for ammonia(NH_(3))synthesis benefiting from its environmental friendliness and sustainability.Cu-based alloys with elemental diversity and adsorption tunability are widely used as electrocatalyst to lower the reaction overpotential for NO_(3)RR catalysis.However,phase separation commonly found in alloys leads to uneven distribution of elements,which limits the possibility of further optimizing the catalytic activity.Herein,an electrotriggered Joule heating method,possessing unique superiority of flash heating and cooling that lead to well-dispersed nanoparticles and uniform mixing of various elements,was adopted to synthesize a single-phase CuNi nano-alloy catalyst evenly dispersed on carbon fiber paper,CFP-Cu_(1)Ni_(1),which exhibited a more positive NO_(3)RR initial potential of 0.1 V versus reversible hydrogen electrode(vs.RHE)than that of pure copper nanoparticles at 10 mA·cm^(−2)in 0.5 mol·L^(−1)Na_(2)SO_(4)+0.1 mol·L^(−1)KNO_(3)solution.Importantly,CFP-Cu_(1)Ni_(1) presented high electrocatalytic activity with a Faradaic efficiency of 95.7%and NH_(3)yield rate of 180.58μmol·h^(−1)·cm^(−2)(2550μmol·h^(−1)·mg_(cat)^(−1))at−0.22 V vs.RHE.Theoretical calculations showed that alloying Cu with Ni into single-phase caused an upshift of its d-band center,which promoted the adsorption of NO_(3)−and weakened the adsorption of NH_(3).Moreover,the competitive adsorption of hydrogen ions was restrained until−0.24 V.This work offers a rational design concept with clear guidance for rapid synthesis of uniformly dispersed single-phase nano-alloy catalyst for efficient electrochemical NO_(3)RR toward ammonia.

纳米多孔Ru掺杂Cu协同调节反应中间体吸附与水分子解离促进电化学硝酸盐还原合成氨

作为能源密集型Haber-Bosch工艺合成氨的一种新兴替代品,电化学硝酸盐还原反应(NO_(3)RR)在可持续合成氨和废水处理方面受到了关注.然而,由于缺乏有效的电催化剂,NO_(3)RR目前仍然面临氨产率低和选择性差的问题.本文报道了通过脱合金法制备的纳米双模式孔Ru掺杂Cu催化剂作为NO_(3)RR的电催化剂,在-0.2 V versus RHE的电位下表现出29.63±0.74 mg h^(-1)mg_(cat.)^(-1)的超高氨产率与97.3%±2.5%的法拉第效率,优于大多数报道的催化剂.密度泛函理论计算表明,在Cu中掺杂Ru可以优化中间体的吸附能,降低NO_(3)RR速控步骤的能垒.此外,Ru原子可以促进H2O的吸附/解离,为含N中间体氢化为NH_(3)提供活性氢.这项工作为NO_(3)RR等过程进行高性能催化剂的合理设计提供了新的途径.

调节Co_(3)O_(4)的价电子结构提高硝酸根还原制氨的催化活性

通过硝酸根电化学还原反应将NO_(3)^(-)转化为NH_(3)是一种有前景的制氨和“绿氢”储存方案.Co_(3)O_(4)对于硝酸根还原析氨反应表现出较高的析氨法拉第效率和稳定性,有望成为理想的催化剂.然而,在Co_(3)O_(4)上发生硝酸根还原反应仍需较高的过电位,从而阻碍了能量转换效率的提升.本文中,我们合成了Cu掺杂Co_(3)O_(4)多孔空心纳米球用作硝酸根还原析氨催化剂.Cu掺杂在保障析氨法拉第效率和稳定性的前提下大幅降低了反应所需的过电位,有效提高了析氨速率.实验和理论分析均表明,Cu掺杂使Co_(3)O_(4)的最高占据态能量上移,缩小了Co_(3)O_(4)的最高占据态与NO_(3)^(-)的最低未占据分子轨道之间的能垒,从而降低了电子从Co_(3)O_(4)向NO_(3)^(-)跃迁所需的过电位,赋予了Cu掺杂Co_(3)O_(4)多孔空心纳米球优异的硝酸根还原析氨电催化活性和耐久性.本研究为纳米材料的电化学性能调控研究提供了新的理论视角.

Atomically precise alkynyl-protected Ag_(20)Cu_(12)nanocluster:Structure analysis and electrocatalytic performance toward nitrate reduction for NH_(3)synthesis

Electrochemical nitrate reduction reaction(NtrRR)has been emerging as an appealing route for both water treatment and NH_(3)synthesis.Herein,we report the structure analysis and electrocatalytic performance of a novel homoleptic alkynyl-protected Ag_(20)Cu_(12)nanocluster(Ag_(20)Cu_(12)in short)with atomic precision,which has eight free electrons and displays characteristic absorbance feature.Single crystal X-ray diffraction(SC-XRD)discloses that,it adopts a Ag_(14)kernel capped by three Ag_(2)Cu_(4)(C≡CArF)_(8)metal–ligand binding motifs in the outer shell.Ag_(20)Cu_(12)exhibited excellent catalytic performance toward NtrRR,as manifested by the superior NH_(3)Faradaic efficiency(FE,84.6%)and yield rate(0.138 mmol·h^(−1)·mg−1)than the homoleptic alkynyl-protected Ag_(32)nanoclusters.Additionally,it demonstrates good catalytic recycling capability.Density functional theory(DFT)calculations revealed that,the de-ligated Ag_(20)Cu_(12)cluster can expose the available AgCu bimetallic sites as the efficient active sites for NH_(3)formation.In particular,the participation of Cu sites greatly facilitates the initial capture of NO_(3)−and simultaneously promotes the selectivity of the final product.This study discovers a novel homoleptic alkynyl-protected AgCu superatom,and offers a great example to elucidate the structure–performance relationship of bimetallic catalyst for NtrRR and other multiple protons/electrons coupled electrocatalytic reactions.

Recent Advances of Cu-Based Materials for Electrochemical Nitrate Reduction to Ammonia

The pollution of nitrate in groundwater has become an environmental problem of general concern due to adverse human and ecological impacts. Treatment of nitrate-rich wastewater is of significance yet challenging for the conventional biological denitrification processes. Electrocatalytic nitrate-to-ammonia conversion emerges as one of the most promising avenues to remove environmentally harmful nitrate from various types of wastewaters while simultaneously producing value-added ammonia. Cu-based materials show great advantages in promoting selective electroreduction of nitrate to ammonia in terms of high nitrate conversion efficiency, ammonia selectivity and ammonia faradaic efficiency thanks to the 3d transition metal structure, low cost, high reserves, and excellent catalytic performance of Cu. In this review, we comprehensively overview the most recent advances in selective electrocatalytic nitrate-to-ammonia conversion using Cu-based materials. Various kinds of Cu-based materials including monometallic Cu catalysts, bimetallic Cu-based catalysts, Cu-based compounds, and Cu-based inorganicorganic hybrid materials and their derivatives are discussed in detail with emphasis on their structural and compositional features and functional mechanisms in promoting nitrate-to-ammonia conversion. Finally, a brief discussion on future directions, challenges and opportunities in this field is also provided.

Grain Boundaries Engineering of Hollow Copper Nanoparticles Enables Highly Efficient Ammonia Electrosynthesis from Nitrate

Electrochemical nitrate reduction reaction(NO_(3)−RR)is an ideal route to produce ammonia(NH_(3))under ambient conditions.Although a markedly improved NH3 production rate has been achieved on the NO_(3)−RR compared with the nitrogen reduction reaction(NRR),the NH_(3) production rate of NO_(3)−RR is still well below the industrial Haber-Bosch route due to the lack of robust electrocatalysts for yielding high current densitieswith concurrently good suppression of hydrogen evolution reaction(HER).Herein,we describe an in situ electrochemical strategy for the synthesis of hollow carbon-coated Cu nanoparticles(NPs)(HSCu@C)with abundant grain boundaries(HSCu-AGB@C)for highly efficient NO_(3)−RR in both alkaline and neutral media.Impressively,in alkaline media,the HSCu-AGB@C can achieve a maximum NH3 Faradaic efficiency of 94.2% with an ultrahigh NH_(3) rate of 487.8 mmol g^(−1) cat h^(−1) at−0.2 V versus a reversible hydrogen electrode,more than 2.4-fold of the rate obtained in the Haber-Bosch.Both theoretic computations and experimental results uncover that the grain boundaries play the key to improve the NO_(3)−RR performance.Herein,the industrial-scale NH_(3) production ratemay open exciting opportunities for the practical electrosynthesis NH_(3) under ambient conditions.