General strategy for evaluating the d-band center shift and ethanol oxidation reaction pathway towards Pt-based electrocatalysts

The catalytic performance of Pt-based catalysts depends sensitively on their d-band centers.Nevertheless,there are still huge challenges to evaluate their d-band centers from experimental technologies,and modulate them to analyze their selectivity in ethanol oxidation reaction(EOR).Here,Pt1Au1alloy supported on the commercial carbon material(Pt_(1)Au_(1)/C)is employed as a typical example to investigate its d-band center shift of surface Pt,and as electrocatalysts to study its selectivity towards EOR.Significantly,a highly reliable in situ Fourier-transform infrared spectroscopy CO-probe strategy is developed to characterize the d-band center shift of surface Pt.The modified electronic effect and site effect of Pt_(1)Au_(1)/C dictated the adsorption configuration of intermediate species and the OH species coverage,thereby influencing its selectivity.More importantly,we developed a universal cyclic voltammetry peak differentiation fitting method as an electrochemical analysis technique to investigate CO_(2)selectivity,which is potentially extendable to other Pt-based electrocatalysts.

Self-supporting trimetallic PtAuBi aerogels as electrocatalyst for ethanol oxidation reaction

The creation of anodic ethanol oxidation reaction catalysts with superior all-around performance for direct ethanol fuel cells(DEFCs)has continued to attract the attention of researchers.An ultrathin trimetallic PtAuBi aerogel with branching,rough-surfaced 1D nanowires that self-assemble into a 3D porous network structure has been created in this study.It has a mass activity(MA)of 8045 mA mgPt^(-1)in an alkaline medium,which is 7.56 times greater than that of commercial Pt/C(1064 mA mgPt^(-1)).Notably,the catalytic activity and resistance to CO poisoning of PtAuBi aerogels are improved by the addition of an efficient"active additive"Au.The results analysis reveals that the increased performance of PtAuBi aerogel is mostly attributable to the integrated function of the 3D porous network structure,the downward shift of the Pt d-band center,and the synergistic effect of the"Pt-Bi"and/or"Pt-Au"dual active sites.

Acetic acid-assisted mild dealloying of fine CuPd nanoalloys achieving compressive strain toward high-efficiency oxygen reduction and ethanol oxidation electrocatalysis

Dealloying by which the transition metal is partially or completely leached from an alloy precursor is an effective way to optimize the fundamental effects for further enhancing the electrocatalysis of a catalyst.Herein,to address the deficiencies associated with the commonly used dealloying methods,for example,electrochemical and sulfuric acid/nitric acid treatment,we report an acetic acid-assisted mild strategy to dealloy Cu atoms from the outer surface layers of CuPd alloy nanoparticles to achieve high-efficiency electrocatalysis for oxygen reduction and ethanol oxidation in an alkaline electrolyte.The leaching of Cu atoms by acetic acid exerts an additional compressive strain effect on the surface layers and exposes more active Pd atoms,which is beneficial for boosting the catalytic performance of a dealloyed catalyst for the oxygen reduction reaction(ORR)and the ethanol oxidation reaction(EOR).In particular,for ORR,the CuPd nanoparticles with a Pd/Cu molar ratio of 2:1 after acetic dealloying show a half-wave potential of 0.912 V(vs.RHE)and a mass activity of 0.213 AmgPd^(-1) at 0.9 V,respectively,while for EOR,the same dealloyed sample has a mass activity and a specific activity of 8.4 Amg^(-1) and 8.23 mA cm^(-2),respectively,much better than their dealloyed counterparts at other temperatures and commercial Pd/C as well as a Pt/C catalyst.

Pt3Ag alloy wavy nanowires as highly effective electrocatalysts for ethanol oxidation reaction

Direct ethanol fuel cell(DEFC)has received tremendous research interests because of the more convenient storage and transportation of ethanol vs.compressed hydrogen.However,the electrocatalytic ethanol oxidation reaction typically requires precious metal catalysts and is plagued with relatively high over potential and low mass activity.Here we report the synthesis of Pt3Ag alloy wavy nanowires via a particle attachment mechanism in a facile solvothermal process.Transmission microscopy studies and elemental analyses show highly wavy nanowire structures with an average diameter of 4.6±1.0 nm and uniform Pt3Ag alloy formation.Electrocatalytic studies demonstrate that the resulting alloy nanowires can function as highly effective electrocatalysts for ethanol oxidation reactions(EOR)with ultrahigh specific activity of 28.0 mA/cm^2 and mass activity of 6.1 A/mg,far exceeding that of the commercial Pt/carbon samples(1.10 A/mg).The improved electrocatalytic activity may be partly attributed to partial electron transfer from Ag to Pt in the Pt3Ag alloy,which weakens CO binding and the CO poisoning effect.The one-dimensional nanowire morphology also contributes to favorable charge transport properties that are critical for extracting charge from catalytic active sites to external circuits.The chronoamperometry studies demonstrate considerably improved stability for long term operation compared with the commercial Pt/C samples,making the Pt3Ag wavy nanowires an attractive electrocatalyst for EOR.

Enabling high-efficiency ethanol oxidation on NiFe-LDH via deprotonation promotion and absorption inhibition

Nucleophile oxidation reaction(NOR), represented by ethanol oxidation reaction(EOR), is a promising pathway to replace oxygen evolution reaction(OER). EOR can effectively reduce the driving voltage of hydrogen production in direct water splitting. In this work, large current and high efficiency of EOR on a Ni, Fe layered double hydroxide(NiFe-LDH) catalyst were simultaneously achieved by a facile fluorination strategy. F in NiFe-LDH can reduce the activation energy of the dehydrogenation reaction, thus promoting the deprotonation process of NiFe-LDH to achieve a lower EOR onset potential. It also weakens the absorption of OH-and nucleophile electrooxidation products on the surface of NiFe-LDH at a higher potential, achieving a high current density and EOR selectivity, according to density functional theory calculations. Based on our experiment results, the optimized fluorinated NiFe-LDH catalyst achieves a low potential of 1.386 V to deliver a 10 mA cm^(-2)EOR. Moreover, the Faraday efficiency is greater than 95%, with a current density ranging from 10 to 250 mA cm^(-2). This work provides a promising pathway for an efficient and cost-effective NOR catalyst design for economic hydrogen production.

Rh-Cu alloy nano-dendrites with enhanced electrocatalytic ethanol oxidation activity

The application of direct ethanol fuel cell(DEFC)has been bottlenecked by the sluggish ethanol oxidation reaction(EOR).Efficient electrocatalysts for the C-C bond cleavage are essential to promote EOR with high efficiency and C1 selectivity.Here,we prepared Rh-Cu alloy nano-dendrites(RhCu NDs)with abundant surface steps through controlled co-reduction,which exhibited significantly enhanced activity and C1 selectivity(0.47 m A cm_((ECSA))^(-2),472.4 mA mg_(Rh)^(-1),and 38.9%)than Rh NDs(0.32 mA cm((ECSA))-2,322.1 mA mgRh-1,and 21.4%)and commercially available Rh/C(0.18 mA cm_((ECSA))^(-2),265.4 mA mg_(Rh)^(-1),and 14.9%).Theoretical calculations and CO-stripping experiments revealed that alloying with Cu could modulate the surface electronic structures of Rh to resist CO-poisoning while strengthening ethanol adsorption.In situ Fourier transform infrared spectroscopy(FTIR)indicated that the surface steps on RhCu NDs further promoted the C-C bond cleavage to increase the C1 selectivity.Therefore,optimizing the surface geometric and electronic structures of nanocrystals by rational composition and morphology control can provide a promising strategy for developing practical DEFC devices.

Porous Pt nanoframes decorated with Bi(OH)3 as highly efficient and stable electrocatalyst for ethanol oxidation reaction

High-quality Pt-based catalysts are highly desirable for ethanol oxidation reaction(EOR),which is of critical importance for the commercial applications of direct ethanol fuel cells(DEFCs).However,most of the Pt-based catalysts have suffered from high cost and low operation durability.Herein a two-step method has been developed to synthesize porous Pt nanoframes decorated with Bi(OH)3,which show excellent catalytic activity and operation durability in both alkaline and acidic media.For example,the nanoframes show a mass activity of 6.87 A·mgPt−1 in alkaline media,which is 13.5-fold higher than that of commercial Pt/C.More importantly,the catalyst can be reactivated simply,which shows negligible activity loss after running for 180,000 s.Further in situ attenuated total reflection-infrared(ATR-IR)absorption spectroscopy and CO-stripping experiments indicate that surface Bi(OH)3 species can greatly facilitate the formation of adsorbed OH species and subsequently remove carbonaceous poison,resulting in a significantly enhanced stability towards EOR.This work may favor the tailoring of desired electrocatalysts with high activity and durability for future commercial application of DEFCs.

Crystal phase-controlled growth of PtCu and PtCo alloys on 4H Au nanoribbons for electrocatalytic ethanol oxidation reaction

Crystal phase can greatly affect the physicochemical properties and applications of nanomaterials.However,it stil remains a great challenge to synthesize nanostructures with the same composition and morphology but different phases in order to explore the phase-dependent properties and applications.Herein,we report the crystal phase-controlled synthesis of PtCu alloy shells on 4H Au nanoribbons(NRBs),referred to as 4H-Au NRBs,to form the 4H-Au@PtCu core-shell NRBs.By tuning the thickness of PtCu,4H-PtCu and face-centered cubic(cc)phase PICu(cc-PtCu)alloy shells are successtully grown on the 4H-Au NRB cores.This thickness-dependent phase-controlled growth strategy can also be used to grow PtCo alloys with 4H or fcc phase on 4H-Au NRBs.Significantly,when used as electrocatalysts for the ethanol oxidation reaction(EOR)in alkaline media,the 4H-Au@4H-PtCu NRBs show much better EOR performance than the 4H-Au@fcc-PtCu NRBs,and both of them possess superior performance compared to the commercial Pt black.Our study provides a strategy on phase-contolled synthesis of nanomaterials used for crystal phase-dependent applications.

Synergistic combination of Pd nanosheets and porous Bi(OH)_(3) boosts activity and durability for ethanol oxidation reaction

Highly active and durable Pd-based electrocatalysts for ethanol oxidation reaction(EOR)play a crucial role in the commercialization of direct ethanol fuel cells(DEFCs).However,the poisonous intermediates(especially adsorbed CO species(COad))formed during the EOR process can easily adsorb and block the active sites on Pd electrodes,which in turn limits the catalytic efficiency.Hence,we present a series of Pd-based composites with a strong coupling interface consisting of Pd nanosheets and amorphous Bi(OH)_(3)species.The incorporation of Bi(OH)3 can induce an electron-rich state adjacent to the Pd sites and effectively separate the Pd ensemble,leading to excellent CO tolerance.The optimal Pd-Bi(OH)_(3)NSs catalyst manifests a mass activity of 2.2 A·mgPd^(-1),which is 5.7 and 2.0 times higher than that of Pd NSs and commercial Pd/C catalyst,respectively.Further CO-stripping experiments and CO-DRIFTS tests confirm the excellent CO tolerance on Pd-Bi(OH)3 NSs electrode,leading to the enhanced EOR durability.

Flexible Au micro-array electrode with atomic-scale Au thin film for enhanced ethanol oxidation reaction

The catalysis of Au thin film could be improved by fabrication of array structures in large area.In this work,nanoimprint lithography has been developed tofabricate flexible Au micro-array(MA)electrodes with~100%coverage.Advanced electron microscopy characterisations have directly visualised the atomic-scale three-dimensional(3D)nanostructures with a maximum depth of 6 atomic layers.In-situ observation unveils the crystal growth in the form of twinning.High double layer capacitance brings about large number of active sites on the Au thin film and has a logarithmic relationship with mesh grade.Electrochemistry testing shows that the Au MAs perform much better ethanol oxidation reaction than the planar sample;MAs with higher mesh grade have a greater active site utilisation ratio(ASUR),which is important to build electrochemical double layer for efficient charge transfer.Further improvement on ASUR is expected for greater electrocatalytic performance and potential application in direct ethanol fuel cell.

Ionic liquid-derived core–shell gold@palladium nanoparticles with tiny sizes for highly efficient electrooxidation of ethanol

To maximize the size and structural advantages of nanomaterials in electrooxidation of ethanol, we herein report the synthesis of core–shell gold(Au)@Palladium(Pd) nanoparticles smaller than 3 nm in an ionic liquid, which combines the advantages of ionic liquids in preparing fine metal nanoparticles with the benefits of core–shell nanostructures. This synthetic strategy relies on the use of an ionic liquid(1-(2'-aminoethyl)-3-methyl-imidazolum tetrafluoroborate) as a stabilizer to produce Au particles with an average size of ca. 2.41 nm, which are then served as seeds for the formation of tiny core–shell Au@Pd nanoparticles with different Au/Pd molar ratios. The strong electronic coupling between Au core and Pd shell endows the Pd shell with an electronic structure favorable for the ethanol oxidation reaction. In specific, the ionic liquidderived core–shell Au@Pd nanoparticles at an Au/Pd molar ratio of 1/1 exhibit the highest mass-and area-based activities, approximately 11 times than those of commercial Pd/C catalyst for ethanol electrooxidation.

Polysulfide modified PtCu intermetallic nanocatalyst with enrichment realizes efficient electrooxidation ethanol to CO_(2)

The main problem faced by ethanol oxidation reaction(EOR)includes low activity,poor selectivity,and durability.In the study,we found that polysulfide modified on the surface of PtCu intermetallic(IM)/C can simultaneously enrich hydroxyl and ethanol,which could effectively improve the catalytic activity,CO_(2) selectivity,and durability of catalyst.The mass activity and the specific activity of the product in 1 M KOH electrolyte reached 17.83 A·mgPt^(-1) and 24.67 mA·cm^(-2).The CO_(2) selectivity of polysulfide modified product achieved 93.5%,which was 30 folds higher than Pt/C.In addition,the catalyst showed high catalytic stability.The mechanism study demonstrates that the surface modified polysulfide could significantly boost the enrichment effect of ethanol and hydroxyl species,accelerating C–C bond cleavage and CO oxidation.

Enhancement of CH_(3)CO^(*) adsorption by editing d-orbital states of Pd to boost C–C bond cleavage of ethanol eletrooxidation

Improving the complete ethanol electrooxidation on Pd-based catalysts in alkaline media has drawn widely attention due to the high mass energy density.However,the weak adsorption energy of CH_(3)CO^(*) on Pd restricts the C–C bond cleavage.Inspired by the molecular orbital theory,we proposed the d-state-editing strategy to construct more unoccupied d-states of Pd for the enhanced interaction with CH_(3)CO^(*) to break C–C bonds.As expected,the reduced number of e_g electrons and more unoccupied d-states of Pd successfully formed on as-prepared porous Rh Au–Pd Cu nanosheets(PNSs).Theoretical calculations show that the optimized d-states of Rh Au–Pd Cu PNS can effectively improve the adsorption of CH_(3)CO^(*) and drastically reduce the energy barrier of C–C bond cleavage,thus boosting the complete oxidation of ethanol.The charge ratio of C_1 pathway on Rh Au–Pd Cu PNSs is 51.5%,more than 2 times higher than that of Pd NSs.Our finding provides an innovative perspective for the design of highly-efficient noble-based electrocatalysts.

MoO_(3)/C-supported Pd nanoparticles as an efficient bifunctional electrocatalyst for ethanol oxidation and oxygen reduction reactions

metal oxide electronic interactions in composite electrocatalysts have a considerable impact on their catalytic capability.In this study,we successfully synthesized an electrocatalytic material composed of MoO_(3)/C speciessupported Pd nanoparticles(Pd-MoO_(3)/C)using a convenient hydrothermal method,which exhibited excellent catalytic activities for both ethanol oxidation and oxygen reduction in KOH media.The specific activity of PdMoO_(3)/C toward ethanol oxidation with MoO_(3)loading(40wt%)was~2.6 times greater than that for the commercial Pd/C(10 wt%)with the same Pd content.In particular,the activity could effectively hold up to~60%of its maximum activity after 500-cycle tests,demonstrating improved cyclical stability.Notably,the fast electron transfer kinetics toward oxygen reduction for Pd-MoO_(3)/C(40%)were also comparable to those of commercial Pt/C(20 wt%)catalysts.These superior electrochemical features are primarily derived from the stronger electronic coupling between Pd and MoO_(3)through charge transfer,which can supply more active centers and improve the anti-poisoning ability.Meanwhile,the MoO_(3)species in the Pd-MoO_(3)/C composite may provide additional benefits in terms of electrical conductivity and dispersion.

Rare earth alloy nanomaterials in electrocatalysis

With the rapid development of society and economy, the excessive consumption of fossil energy has led to the global energy and environment crisis. In order to explore the sustainable development of new energy, research based on electrocatalysis has attracted extensive attention in the academic circle. The main challenge in this field is to develop nano-catalysts with excellent electrocatalytic activity and selectivity for target products. The state of the active site in catalyst plays a decisive role in the activity and selectivity of the reaction. In order to design efficient and excellent catalysts, it is an effective means to adjust the electronic structure of catalysts. Electronic effects are also called ligand effects. By alloying with rare earth(RE) elements, electrons can be redistributed between RE elements and transition metal elements, achieving accurate design of the electronic structure of the active site in the alloy. Because of the unique electronic structure of RE, it has been paid attention in the field of catalysis. The outermost shell structure of RE elements is basically the same as that of the lower shell, except that the number of electrons in the 4f orbital is different, but the energy level is similar, so their properties are very similar. When RE elements form compounds, both the f electrons in the outermost shell and the d electrons in the lower outer shell can participate in bonding. In addition, part of the 4f electrons in the third outer shell can also participate in bonding.In order to improve the performance of metal catalysts, alloying provides an effective method to design advanced functional materials. RE alloys can integrate the unique electronic structure and catalytic behavior of RE elements into metal materials, which not only provides an opportunity to adjust the electronic structure and catalytic activity of the active component, but also enhances the structural stability of the alloy and is expected to significantly improve the catalytic performance of the catalyst. From the perspective of electronic and catalytic activity, RE elements have unique electronic configuration and lanthanide shrinkage effect. Alloying with RE elements will make the alloy have more abundant electronic structure, activity, and spatial arrangement, effectively adjusting the reaction kinetics of the electrochemical process of the catalyst. In this paper, the composition,structure, synthesis of RE alloys and their applications in the field of electrocatalysis are summarized, including the hydrogen evolution reaction, the oxygen evolution reaction, the oxygen reduction reaction, the methanol oxidation reaction, the ethanol oxidation reaction, and other catalytic reactions. At the same time, the present challenges of RE alloy electrocatalytic materials are summarized and their future development direction is pointed out. In the field of electrocatalysis, the cost of catalyst is too high and the stability is not strong. Therefore, the testing process should be related to the actual application, and the test method should be standardized, so as to carry forward the field of electrocatalysis.

Single-Site Cu-Doped PdSn Wavy Nanowires for Highly Active,Stable,and CO-Tolerant Ethanol Oxidation Electrocatalysis

Developing a catalyst to break the tradeoff relation-ship between the catalytic activity and antipoisoning property toward the ethanol oxidation reaction(EOR)is of critical importance to the development of direct ethanol fuel cells(DEFCs),but remains challenging.Here,we developed a unique class of single-site Cu-doped PdSn wavy nanowires(denoted as SS Cu−PdSn WNWs)with promoted activity and durability toward alkaline EOR.Detailed characterizations reveal the atomic isolation of Cu species dispersed on the surface of the PdSn WNWs with distinct wavy structure and grain boundaries.The created SS Cu−PdSn WNWs exhibit an enhanced EOR performance in terms of mass activity,which is higher than those of PdSn WNWs,commercial Pd black,and commercial Pd/C,respectively.Moreover,the SS Cu−PdSn WNWs can also show improved stability as compared to other catalysts due to the improved antipoisoning property from the unique surface anchoring structure.Further investigations demonstrate that the doped SS Cu can strongly inhibit the adsorption of CO and promote the reaction process of EOR.DFT results reveal that the doped Cu shifts down the d-band center of PdSn,thereby modifying the adsorption of intermediates and reducing the reaction barrier of EOR.This work maps a pathway for optimally boosting EOR performance with surface engineering via atomic doping.

Unraveling the role of iron on Ni-Fe alloy nanoparticles during the electrocatalytic ethanol-to-acetate process

The anodic electrooxidation of ethanol to value-added acetate is an excellent example of replacing the oxygen evolution reaction to promote the cathodic hydrogen evolution reaction and save energy.Herein,we present a colloidal strategy to produce Ni-Fe bimetallic alloy nanoparticles(NPs)as efficient electrocatalysts for the electrooxidation of ethanol in alkaline media.Ni-Fe alloy NPs deliver a current density of 100 mA·cm^(-2) in a 1.0 M KOH solution containing 1.0 M ethanol merely at 1.5 V vs.reversible hydrogen electrode(RHE),well above the performance of other electrocatalysts in a similar system.Within continuous 10 h testing at this external potential,this electrode is able to produce an average of 0.49 mmol·cm^(-2)·h^(-1) of acetate with an ethanol-to-acetate Faradaic efficiency of 80%.A series of spectroscopy techniques are used to probe the electrocatalytic process and analyze the electrolyte.Additionally,density functional theory(DFT)calculations demonstrate that the iron in the alloy NPs significantly enhances the electroconductivity and electron transfer,shifts the rate-limiting step,and lowers the energy barrier during the ethanol-to-acetate reaction pathway.

Facile one-step synthesis of PdPb nanochains for high-performance electrocatalytic ethanol oxidation

The widespread application of direct ethanol fuel cells is hampered due to the low activity,high cost and poor operation durability of electrocatalysts for ethanol oxidation reaction(EOR).Herein,we report a one-pot synthetic method to synthesize PdPb3 nanochains with well-defined shape,size and composition via a solution-phase reduction method.The morphology,composition distribution and structure characteristics of PdPb3 nanochains were investigated by transmission electron microscopy,X-ray photoelectron spectroscopy and X-ray diffraction.Thanks to the unique structure,the as-obtained PdPb3 nanochains can manifest much higher mass activity(2523 mA·mg-1)and higher operation durability than commercial Pd/C(1272 mA·mg-1)during the EOR measurements.More importantly,further CO-stripping measurements indicate that the incorporation of Pb species could favor the oxidative removal of CO intermediates on the Pd electrode at the negative potential and enhance the EOR activity and stability,making it possible to develop highly active and durable electrocatalysts.

Five-fold twinned Ir-alloyed Pt nanorods with high C1 pathway selectivity for ethanol electrooxidation

Developing efficient and robust electrocatalysts toward ethanol oxidation reaction(EOR)with high C1 pathway selectivity is critical for commercialization of direct ethanol fuel cells(DEFCs).Unfortunately,current most EOR electrocatalysts suffer from rapid activity degradation and poor C1 pathway selectivity for complete oxidation of ethanol.Herein,we report a novel electrocatalyst of five-fold twinned(FFT)Ir-alloyed Pt nanorods(NRs)toward EOR.Such FFT Pt-Ir NRs bounded by five(100)facets on the sides and ten(111)facets at two ends possess high percentage of(100)facets with tensile strain.Owing to the inherent characteristics of the FFT NR and Ir alloying,the as-prepared FFT Pt-Ir NRs display excellent alkaline EOR performance with a mass activity(MA)of 4.18 A·mgPt^(-1),a specific activity(SA)of 10.22 mA·cm^(-2),and a Faraday efficiency of 61.21%for the C1 pathway,which are 6.85,5.62,and 7.70 times higher than those of a commercial Pt black,respectively.Besides,our catalyst also exhibits robust durability.The large percentage of open tensile-strained(100)facets and Ir alloying significantly promote the cleavage of C-C bonds and facilitate oxidation of the poisonous intermediates,leading to the transformation of the dominant reaction pathway for EOR from C2 to C1 pathway,and effectively suppress the deactivation of the catalyst.

Carbon Dots Promote the Performance of Anodized Nickel Passivation Film on Ethanol Oxidation by Enhancing Oxidation of the Intermediate

Ethanol is considered a better fuel than methanol in direct alcohol fuel cells because of the high energy density and low toxicity.Compared with noble metal catalysts,nickel-based catalysts are much cheaper in price.However,present nickel-based catalysts still surfer from some disadvantages such as low activity and high overpotential.In this paper;we show a new and high efficient nickel-based catalyst for ethanol oxidation.A layer of anodized nickel passivation film(Ni-APF)was formed on the surface of nickel sheet by anodic oxidation method with carbon dots(CDs)as co-catalyst.At the current density of 110 mA·cm^(-2),the potential for Ni-APF/CDs was only 0.541 V(vs.Ag/AgCI),which was 18.8% lower than that of Ni-APF.Low overpotential could reduce electrode thermal loss and increase output energy.Ni-APF/CDs showed 144.4 mA·cm^(-2) peak current density at peak potential 0.662 V(vs.Ag/AgCI),which was 31% higher than that of Ni-APF(110.3 mA·cm^(-2)).In this system,CDs mainly function in the increase of charge-transfer capacity and the promotion oxidation of carbonaceous intermediates.