In operando-formed interface between silver and perovskite oxide for efficient electroreduction of carbon dioxide to carbon monoxide

Electrochemical carbon dioxide(CO_(2))reduction(ECR)is a promising technology to produce valuable fuels and feedstocks from CO_(2).Despite large efforts to develop ECR catalysts,the investigation of the catalytic performance and electrochemical behavior of complex metal oxides,especially perovskite oxides,is rarely reported.Here,the inorganic perovskite oxide Ag-doped(La_(0.8)Sr_(0.2))_(0.95)Ag_(0.05)MnO_(3-δ)(LSA0.05M)is reported as an efficient electrocatalyst for ECR to CO for the first time,which exhibits a Faradaic efficiency(FE)of 84.3%,a remarkable mass activity of 75Ag^(-1)(normalized to the mass of Ag),and stability of 130 h at a moderate overpotential of 0.79 V.The LSA0.05M catalyst experiences structure reconstruction during ECR,creating the in operando-formed interface between the perovskite and the evolved Ag phase.The evolved Ag is uniformly distributed with a small particle size on the perovskite surface.Theoretical calculations indicate the reconstruction of LSA0.05M during ECR and reveal that the perovskite-Ag interface provides adsorption sites for CO_(2) and accelerates the desorption of the*CO intermediate to enhance ECR.This study presents a novel high-performance perovskite catalyst for ECR andmay inspire the future design of electrocatalysts via the in operando formation of metal-metal oxide interfaces.

Electron-Deficient Zn-N_(6) Configuration Enabling Polymeric Carbon Nitride for Visible-Light Photocatalytic Overall Water Splitting

Despite of suitable band structures for harvesting solar light and driving water redox reactions,polymeric carbon nitride(PCN)has suffered from poor charge transfer ability and sluggish surface reaction kinetics,which limit its photocatalytic activity for water splitting.Herein,atomically dispersed Zn-coordinated three-dimensional(3D)sponge-like PCN(Zn-PCN)is synthesized through a novel intermediate coordination strategy.Advanced characterizations and theoretical calculations well evidence that Zn single atoms are coordinated and stabilized on PCN in the form of Zn-N_(6) configura-tion featured with an electron-deficient state.Such an electronic configuration has been demonstrated contributive to promoted electron excitation,accelerated charge separation and transfer as well as reduced water redox barriers.Further benefited from the abundant surface active sites derived from the 3D porous structure,Zn-PCN realizes visible-light photocatalysis for overall water splitting with H_(2) and O_(2) simultaneously evolved at a stoichiometric ratio of 2:1.This work brings new insights into the design of novel single-atom photocatalysts by deepening the understanding of electronic configurations and reactive sites favorable to excellent photocatalysis for water splitting and related solar energy conversion reactions.

Controllable synthesis of Fe–N4 species for acidic oxygen reduction

Controllable design and synthesis of catalysts with the target active sites are extremely important for their applications such as for the oxygen reduction reaction(ORR)in fuel cells.However,the controllably synthesizing electrocatalysts with a single type of active site still remains a grand challenge.In this study,we developed a facile and scalable method for fabricating highly efficient ORR electrocatalysts with sole atomic Fe-N4 species as the active site.Herein,the use of cost-effective highly porous carbon as the support not only could avoid the aggregation of the atomic Fe species but also a feasible approach to reduce the catalyst cost.The obtained atomic Fe-N4 in activated carbon(aFe@AC)shows excellent ORR activity.Its half-wave potential is 59 mV more negative but 47 mV more positive than that of the commercial Pt/C in acidic and alkaline electrolytes,respectively.The full cell performance test results show that the aFe@AC sample is a promising candidate for direct methanol fuel cells.This study provides a general method to prepare catalysts with a certain type of active site and definite numbers.

Promoting surface reconstruction of NiFe layered double hydroxides via intercalating[Cr(C_(2)O_(4))_(3)]^(3-)for enhanced oxygen evolution

Rationally manipulating surface reconstruction of catalysts for water oxidation,inducing formation and dynamic accumulation of catalytically active centers still face numerous challenges.Herein,the introduction of[Cr(C_(2)O_(4))_(3)]^(3-)into NiFe LDHs by intercalation engineering to promote surface reconstruction achieves an advanced oxygen evolution reaction(OER)activity.In view of the weak electronegativity of Cr^(3+) in[Cr(C_(2)O_(4))_(3)]^(3-),the intercalation of[Cr(C_(2)O_(4))_(3)]^(3-)is expected to result in an electron-rich structure of Fe sites in NiFe LDHs,and higher valence state of Ni can be formed with the charge transfer between Fe and Ni.The optimized electronic structure of NiFe-[Cr(C_(2)O_(4))_(3)]^(3-)-LDHs with more active Ni^(3+) species and the expedited dynamic generation of Ni^(3+) (Fe)OOH phase during the OER process contributed to its excellent catalytic property,revealed by in situ X-ray absorption spectroscopy,Raman spectroscopy,and quasi-in situ X-ray photoelectron spectroscopy.With the modulated electronic structure of metal sites,NiFe-[Cr(C_(2)O_(4))_(3)]^(3-)-LDHs exhibited promoted OER property with a lower overpotential of 236 mV at the current density of 10 mA cm^(-2).This work illustrates the intercalation of conjugated anion to dynamically construct desired Ni^(3+) sites with the optimal electronic environment for improved OER electrocatalysis.

Activity origin and alkalinity effect of electrocatalytic biomass oxidation on nickel nitride

Electro-oxidation of 5-hydroxymethylfurfural(HMFOR)is a promising green approach to realize the conversion of biomass into value-added chemicals.However,considering the complexity of the molecular structure of HMF,an in-depth understanding of the electrocatalytic behavior of HMFOR has rarely been investigated.Herein,the electrocatalytic mechanism of HMFOR on nickel nitride(Ni3 N)is elucidated by operando X-ray absorption spectroscopy(XAS),in situ Raman,quasi in situ X-ray photoelectron spectroscopy(XPS),and operando electrochemical impedance spectroscopy(EIS),respectively.The activity origin is proved to be Ni^(2+δ)N(OH)ads generated by the adsorbed hydroxyl group.Moreover,HMFOR on Ni3 N relates to a two-step reaction:Initially,the applied potential drives Ni atoms to lose electrons and adsorb OH-after 1.35 VRHE,giving rise to Ni^(2+δ)N(OH)ads with the electrophilic oxygen;then Ni^(2+δ)N(OH)ads seizes protons and electrons from HMF and leaves as H_(2) O spontaneously.Furthermore,the high electrolyte alkalinity favors the HMFOR process due to the increased active species(Ni^(2+δ)N(OH)ads)and the enhanced adsorption of HMF on the Ni3 N surface.This work could provide an in-depth understanding of the electrocatalytic mechanism of HMFOR on Ni3 N and demonstrate the alkalinity effect of the electrolyte on the electrocatalytic performance of HMFOR.

Structurally ordered high-entropy intermetallic nanoparticles with enhanced C–C bond cleavage for ethanol oxidation

Efficient ethanol oxidation reaction(EOR)is challenging due to the multiple reaction steps required to accomplish full oxidation to CO_(2) in fuel cells.Highentropy materials with the adjustable composition and unique chemical structure provide a large configurational space for designing high-performance electrocatalysts.Herein,a new class of structurally ordered PtRhFeNiCu high-entropy intermetallics(HEIs)is developed as electrocatalyst,which exhibits excellent electrocatalytic activity and CO tolerance for EOR compared to high-entropy alloys(HEAs)comprising of same elements.When the HEIs are used as anode catalysts to be assembled into a high-temperature polybenzimidazole-based direct ethanol fuel cell,the HEIs achieve a high power density of 47.50 mW/cm^(2),which is 2.97 times of Pt/C(16.0mW/cm^(2)).Online gas chromatography measurements show that the developed HEIs have a stronger C–C bond-breaking ability than corresponding HEAs and Pt/C catalysts,which is further verified by density functional theory(DFT)calculations.Moreover,DFT results indicate that HEIs possess higher stability and electrochemical activity for EOR than HEAs.These results demonstrate that the HEIs could provide a new platform to develop highperformance electrocatalysts for broader applications.

Surface sulfurization activating hematite nanorods for efficient photoelectrochemical water splitting

Surface treatment is an effective method to improve the photoelectrochemical(PEC) performance of photoelectrodes. Herein, we introduced a novel strategy of surface sulfurization to modify hematite(a-Fe2 O3)nanorods grown in an aqueous solution, which triggered encouraging improvement in PEC performances.In comparison to the solution-grown pristine a-Fe2 O3 nanorod photoanode that is PEC inefficient and always needs high temperature(>600 °C) activation, the surface sulfurized a-Fe2 O3 nanorods show photocurrent density increased by orders of magnitude, reaching 0.46 mA cmà2 at 1.23 V vs. RHE(reversible hydrogen electrode) under simulated solar illumination. This improvement in PEC performances should be attributed to the synergy of the increased carrier density, the reduced surface charge carrier recombination and the accelerated water oxidation kinetics at the a-Fe2 O3/electrolyte interface, as induced by the incorporation of S ions and the formation of multi-state S species(Fe-Sx-Oy) at the surface of a-Fe2 O3 nanorods. This study paves a new and facile approach to activate a-Fe2 O3 and even other metal oxides as photoelectrodes for improved PEC water splitting performances, by engineering the surface structure to relieve the bottlenecks of charge transfer dynamics and redox reaction kinetics at the electrode/electrolyte interface.

调控超细高熵合金晶格应变用于高活性和高稳定性甲醇氧化

高熵合金(HEAs)因其非常规的组成和独特的物理化学性质而得到广泛研究.本文,我们首次提出了一种表面应变策略来调控HEAs的电子结构用于高效的甲醇电氧化反应(MOR).高分辨像差校正扫描透射电子显微镜(STEM)和元素分布分析表明,在Pt Fe CoNi Cu HEAs中各原子分散均匀,并形成FCC晶体结构.700℃热处理所得HEA-700的压缩应变比400℃热处理所得HEA-400的压缩应变高0.94%.正如预期,HEA-700的比活性和质量活性远超HEA-400和目前大多数最先进的催化剂.MOR活性的增强归因于压缩应变导致HEA-700中Pt–Pt键距缩短.同时,核中的非贵金属原子通过转移电子到表面Pt层产生压缩应变和d带中心的下移.这项工作为高性能HEAs电催化剂的设计提供了一个新的视角.

Hierarchically nanostructured Ni O-Co3O4 with rich interface defects for the electro-oxidation of 5-hydroxymethylfurfural

Ni-based electrocatalysts with strong redox abilities are active for the electrochemical oxidation of 5-hydroxymethylfurfural(HMF). Interface engineering is an efficient way to modulate the electronic structure, tune the intermediate adsorption, and expose more active sites. Herein, we increased the concentration of interfacial sites with rich defects in a 3D hierarchical nanostructured NiO-Co3O4 electrocatalyst and investigated its catalytic performance for HMF electro-oxidation. The interface effect created abundant cation vacancies, modulated the electronic properties of Co and Ni atoms, and raised the oxidation state of Ni species. The NiO-Co3O4 catalysts show superb HMF oxidation activities with a low onset potential of 1.28 VRHE.Meanwhile, in-situ surface-selective vibrational spectroscopy of sum-frequency generation was performed to study the reaction pathway during the oxidation process on the electrocatalysts. The current study offers an efficient way to create cation vacancies and proves the decisive role of cation vacancies in catalyzing the HMF electro-oxidation.

In Situ Exfoliation and Pt Deposition of Antimonene for Formic Acid Oxidation via a Predominant Dehydrogenation Pathway

Direct formic acid fuel cell(DFAFC)has been considered as a promising energy conversion device for stationary and mobile applications.Advanced platinum(Pt)electrocatalysts for formic acid oxidation reaction(FAOR)are critical for DFAFC.However,the oxidation of formic acid on Pt catalysts often occurs via a dual pathway mechanism,which hinders the catalytic activity owing to the CO poisoning.Herein,we directly exfoliate bulk antimony to 2D antimonene(Sb)and in situ load Pt nanoparticles onto antimonene sheets with the assistance of ethylenediamine.According to the Bader charge analysis,the charge transfer from antimonene to Pt occurs,confirming the electronic interaction between Pt and Sb.Interestingly,antimonene,as a cocatalyst,alters the oxidation pathway for FAOR over Pt catalyst and makes FAOR follow the more efficient dehydrogenation pathway.The density functional theory(DFT)calculation demonstrates that antimonene can activate Pt to be a lower oxidative state and facilitate the oxidation of HCOOH into CO_(2) via a direct pathway,resulting in a weakened intermediate binding strength and better CO tolerance for FAOR.The specific activity of FAOR on Pt/Sb is 4.5 times,and the mass activity is 2.6 times higher than the conventional Pt/C.

同时构建高结晶氮化碳同型异质结并构筑单原子活性位点促进光催化制氢性能

石墨相氮化碳类光催化剂在光催化制氢应用中展示了巨大潜力.本文提出了一种同时构建高结晶氮化碳同型异质结并构筑单原子活性位点的策略.研究发现在离子热合成中加入钻盐,能促进庚嗪基结晶氮化碳(CCN)向三嗪基结晶氮化碳(PTI)的相变,同时,钴盐可作为单原子钴活性位点的金属源.该Co-CCN/PTI光催化剂在425 nm处达到了20.88%的表观量子效率,在可见光波段(λ>420 nm)达到了3538 Nmol h^(-1)g^(-1)的制氢速率,该速率分别比CCN高4.8倍,比PTI高27.6倍.分析结果表明,CCN/PTI之问的TypeⅡ同型异质结可有效促进电荷分离,Co单原子活性位点可加速表面氧化反应,这两方面因素同时促进光催化制氢性能的提高.

Regulation on polymerization degree and surface feature in graphitic carbon nitride towards efficient photocatalytic H2 evolution under visible-light irradiation

A kind of graphitic carbon nitride(TSC-550) with high polymerization degree and improved surface property was prepared by a new precursor of thiosemicarbazide. The sulfur motif and high nitrogen content in thiosemicarbazide promoted the polymerization of thiosemicarbazide to form graphitic carbon nitride framework with high degree of polymerization, which significantly influenced the electronic structure and surface chemical properties. TSC-550 possessed a narrow bandgap of 2.19 eV that facilitated the utilization of visible light, and possessed a less positive charge, acidic surface that resulted in enhanced hydrogen adsorption ability in water solution, which promoted the H;evolution kinetics. In addition, the extended π-conjugated electronic system promoted the separation and migration of photogenerated charge carries in plane of TSC-550 framework, as well as the increasing interlayer C–N interactions in TSC-550 created conductive paths across the layers to tunnel interlayers for rapid electron transportation. As a result, TSC-550 nanosheets showed excellent photocatalytic H;production activity,the AQY achieved 36.4% at 425 nm.

Manipulating metal-oxygen local atomic structures in singlejunctional p-Si/WO_(3) photocathodes for efficient solar hydrogen generation

Self-passivation in aqueous solution and sluggish surface reaction kinetics significantly limit the photoelectrochemical(PEC)performances of silicon-based photoelectrodes.Herein,a WO_(3) thin layer is deposited on the p-Si substrate by pulsed laser deposition(PLD),acting as a photocathode for PEC hydrogen generation.Compared to bare p-Si,the single-junctional p-Si/WO_(3) photoelectrodes exhibit excellent and stable PEC performances with significantly increased cathodic photocurrent density and exceptional anodic shift in onset potential for water reduction.It is revealed that the WO_(3) layer could reduce the charge transfer resistance across the electrode/electrolyte interface by eliminating the effect of Fermi level pinning on the surface of p-Si.More importantly,by varying the oxygen pressures during PLD,the collaborative modulation of W–O bond covalency and WO6 octahedral structure symmetry contributes to the promoted charge carrier transport and separation.Meanwhile,a large band bending at the p-Si/WO_(3) junction,induced by the optimized O vacancy contents in WO_(3),could provide a photovoltage as high as~500 mV to efficiently drive charge transfer to overcome the water reduction overpotential.Synergistically,by manipulating W–O local atomic structures in the deposited WO_(3) layer,a great improvement in PEC performance could be achieved over the singlejunctional p-Si/WO_(3) photocathodes for solar hydrogen generation.

Interlayer ligand engineering of β-Ni(OH)2 for oxygen evolution reaction

Oxygen evolution reaction(OER)is a bottleneck process for many electrochemical devices due to the sluggish kinetics,for which advanced electrocatalysts should be carefully designed.Nickle-based materials have been extensively studied to catalyze OER.However,their performances are still below the expectation and the active sites are often controversial.Herein,we have successfully modulated the electronic and surface properties of layeredβ-Ni(OH)2 by the interlayer ligand engineering,aiming to design novel efficient electrocatalysts and unveil the catalysis mechanism.By one-step solvothermal reaction,alkoxyl substitutedβ-Ni(OH)2 with variable interlayer distances is obtained,and the ethoxyl substituted one(NiEt)shows great potential for efficient OER.With the assistance of powder X-ray diffraction and crystalline structure computational simulation,the formula of alkoxyl substitutedβ-Ni(OH)2 are determined.Operando X-ray absorption spectroscopy studies combined with ex-situ analyses revealed that the critical active species of NiEt is formed via hydroxylation and subsequent de-protonation,with high valent Niδ+(3<δ≤3.66).The corresponding catalytic reaction pathway and mechanism are proposed.

Promoting the electrochemical hydrogenation of furfural by synergistic Cu^(0)−Cu^(+) active sites

Electrochemical hydrogenation(ECH)of furfural,which uses the proton from water and avoids the usage of gaseous hydrogen and high pressure,is an efficient way to utilize biomass energy.Cu-based catalysts are promising catalysts for the ECH of furfural.However,their active sites and reaction mechanism have not been fully understood yet.This work unveils the active oxidation state of Cu-based electrocatalysts for the ECH of furfural.The co-existence of Cu^(+)and Cu^(0) on the CuO surface under the working potential is confirmed by a series of in situ characterizations.The poisoning experiment shows that the performance decreased heavily after the Cu^(+)was complexed with SCN−,indicating the decisive role of Cu^(+).Finally,the density functional theory(DFT)calculation suggests that the Cu^(0)−Cu^(+)synergistic effect is beneficial to both kinetics and thermodynamics:Cu^(+)accelerates the second step hydrogenation process of furfural,and Cu^(0) reduces the energy barrier for the desorption of furfuryl alcohol.This work demonstrates the synergistic effect of Cu^(0) and Cu^(+)states for the electrochemical hydrogenation of furfural and provides a deeper understanding of the furfural hydrogenation mechanism.