Enhancing water-dissociation kinetics and optimizing intermediates adsorption free energy of cobalt phosphide via high-valence Zr incorporating for alkaline water electrolysis

Developing high-efficiency electrocatalysts for hydrogen evolution reaction(HER) and oxygen evolution reaction(OER) is required to enhance the sluggish kinetics of water dissociation and optimize the adsorption free energy of reaction intermediates.Herein,we tackle this challenge by incorporating high-valence Zr into CoP(ZrxCo_(1-x)P),which significantly accelerates the elementary steps of water electrolysis.Theoretical calculations indicate that the appropriate Zr incorporation effectively expedites the sluggish H2O dissociation kinetics and optimizes the adsorption energy of reaction intermediates for boosting the alkaline water electrolysis.These are confirmed by the experimental results of Zr_(0.06)Co_(0.94)P catalyst that delivers exceptional electrochemical activity.The overpotentials at the current density of 10 mA cm^(-2)(j10) are only 62(HER) and 240 mV(OER) in alkaline media.Furthermore,the Zr_(0.06)Co_(0.94)P/CC‖Zr_(0.06)Co_(0.94)P/CC system exhibits superior overall water splitting activity(1.53 V/j10),surpassing most of the reported bifunctional catalysts.This high-valence Zr incorporation and material design methods explore new avenues for realizing high-performance non-noble metal electrocatalysts.

Kinetically and thermodynamically expediting elementary steps via high-valence Cr-incorporated of nickel selenide for water electrolysis

Designing high-performance electrocatalysts toward hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)is essential to reduce the activation barrier and optimize free adsorption energy of reactive intermediates.Herein,we report that incorporating high-valence Cr into NiSe_(2)(Cr_(x)Ni_(1-x)Se_(2))kinetically and thermodynamically expedites elementary steps of both HER and OER.The as-prepared Cr_(0.05)Ni_(0.95)Se_(2) catalyst displays excellent HER and OER activities,with low overpotentials of 89 and 272 mV at the current density of 10 mA·cm^(-2)(j10),respectively,and remains stable during operation for 30 h.A low cell voltage of only 1.59 V is required to drive j10 in alkaline media.In situ Raman spectroscopy reveals that Cr incorporation facilitates the formation of NiOOH active species during the OER process.Meanwhile,theoretical explorations demonstrate that high-valence Cr incorporation efficiently accelerates water dissociation kinetics and improves H*adsorption during HER process,lowering the activation barrier of OER and optimizing the adsorption energy of oxygen-based intermediate,thus kinetically and thermodynamically enhancing the intrinsic performance of NiSe_(2) for over water splitting.This strategy provides a new horizon to design transition metal based electrocatalysts in the clean energy field.

Topotactically constructed nickel-iron(oxy)hydroxide with abundant in-situ produced high-valent iron species for efficient water oxidation

The low efficiency of oxygen evolution reaction(OER) is regarded as one of the major roadblocks for metal-air batteries and water electrolysis.Herein,a high-performance OER catalyst of NiFe_(0.2)(oxy)hydroxide(NiFe_(0.2)-O_(x)H_(y)) was developed through topotactic transformation of a Prussian blue analogue in an alkaline solution,which exhibits a low overpotential of only 263 mV to reach a current density of 10 mA cm^(-2) and a small Tafel slope of 35 mV dec-1.Ex-situ/operando Raman spectroscopy results indicated that the phase structure of NiFe_(0.2)-O_(x)H_(y) was irreversibly transformed from the type of α-Ni(OH)_(2) to γ-NiOOH with applying an anodic potential,while ex-situ/operando 57Fe Mossbauer spectroscopic studies evidenced the in-situ production of abundant high-valent iron species under OER conditions,which effectively promoted the OER catalysis.Our work elucidates that the amount of high-valent iron species in-situ produced in the NiFe(oxy)hydroxide has a positive correlation with its water oxidation reaction performance,which further deepens the understanding of the mechanism of NiFe-based electrocatalysts.

In Situ Electrochemical Mn(Ⅲ)/Mn(Ⅳ) Generation of Mn(Ⅱ)O Electrocatalysts for High-Performance Oxygen Reduction

Among various earth-abundant and noble metal-free catalysts for oxygen reduction reaction(ORR),manganese-based oxides are promising candidates owing to the rich variety of manganese valence.Herein,an extremely facile method for the synthesis of cubic and orthorhombic phase coexisting Mn(Ⅱ)O electrocatalyst as an efficient ORR catalyst was explored.The obtained MnO electrocatalyst with oxygen vacancies shows a significantly elevated ORR catalytic activity with a half-wave potential(E1/2) of as high as 0.895 V,in comparison with that of commercial Pt/C(E1/2=0.877 V).More impressively,the MnO electrocatalyst exhibits a marked activity enhancement after test under a constant applied potential for 1000 s thanks to the in situ generation and stable presence of high-valence manganese species(Mn^3+ and Mn^4+) during the electrochemical process,initiating a synergetic catalytic effect with oxygen vacancies,which is proved to largely accelerate the adsorption and reduction of O_2 molecules favoring the ORR activity elevation.Such an excellent ORR catalytic performance of this MnO electrocatalyst is applied in Zn-air battery,which shows an extra-high peak power density of 63.2 mW cm^-2 in comparison with that(47.4 m W cm^-2) of commercial Pt/C under identical test conditions.

Structural transformation of metal–organic framework with constructed tetravalent nickel sites for efficient water oxidation

A mixture of Ni and Fe oxides is among the most commonly active catalysts for the oxygen evolution reaction(OER)during the water oxidation process.In particular,Ni oxide incorporated with even a small amount of Fe leads to substantively enhanced OER activity.However,the critical role of Fe species during the electrocatalytic process is still under evaluation.Herein,we report nickel(oxy)hydroxide incorporated with Fe through the surface reconstruction of a bimetallic metal-organic framework(NiFe-MOF)during the water oxidation process.The spectroscopic investigations with theoretical calculations reveal the critical role of Fe in promoting the formation of highly oxidized Ni^(4+),which directly correlates with an enhanced OER activity.Both the geometric and electronic structu res of the as-reconstructed Ni_(1-x)Fe_(x)OOH electrocatalysts can be delicately tuned by the Ni-Fe ratio of the bimetallic NiFe-MOF,further affecting the catalytic activity.As a result,the Ni_(1-x)Fe_(x)OOH derived from Ni_(0.9)Fe_(0.1)-MOF delivers low overpotentials of 260 mV at 10 mA cm^(-2)and 400 mV at 300 mA cm^(-2).

Nanopore-rich NiFe LDH targets the formation of the high-valent nickel for enhanced oxygen evolution reaction

Nickel-iron layered double hydroxides(NiFe LDHs)represent a promising candidate for oxygen evolution reaction(OER),however,are still confronted with insufficient activity,due to the slow kinetics of electrooxidation of Ni^(2+)cations for the high-valent active sites.Herein,nanopore-rich NiFe LDH(PR-NiFe LDH)nanosheets were proposed for enhancing the OER activity together with stability.In the designed catalyst,the confined nanopores create abundant unsaturated Ni sites at edges,and decrease the migration distance of protons down to the scale of their mean free path,thus promoting the formation of high-valent Ni^(3+)/^(4+)active sites.The unique configuration further improves the OER stability by releasing the lattice stress and accelerating the neutralization of the local acidity during the phase transformation.Thus,the optimized PR-NiFe LDH catalysts exhibit an ultralow overpotential of 278 mV at 10 mA∙cm^(−2)and a small Tafel slope of 75 mV∙dec^(−1),which are competitive among the advanced LDHs based catalysts.Moreover,the RP-NiFe LDH catalyst was implemented in anion exchange membrane(AEM)water electrolyzer devices and operated steadily at a high catalytic current of 2 A over 80 h.These results demonstrated that PR-NiFe LDH could be a viable candidate for the practical electrolyzer.This concept also provides valuable insights into the design of other catalysts for OER and beyond.

High-valance molybdenum doped Co_(3)O_(4) nanowires:Origin of the superior activity for 5-hydroxymethyl-furfural oxidation

Co_(3)O_(4) has been widely explored in electrocatalytic 5-hydroxymethyl-furfural(HMF) oxidation. However,the poor intrinsic ability has seriously limited its electrochemical ability. Heteroatom-doping is an efficient method to enhance the electrocatalytic ability of catalyst by regulating electronic structure. Herein,we have modulated the electronic structure of Co_(3)O_(4) by high valance Mo^(6+)-doping. With the introduction of Mo^(6+), the content of Co^(2+) was increased and metal-oxygen bond was strength. Electrochemical results suggested that the electrocatalytic ability of Co_(3)O_(4) towards HMF oxidation has been dramatically improved and reaction kinetics has been fasten. Theoretical calculations demonstrated that the surrounding cobalt sites after Mo^(6+)-doping with assembled electron has a strong adsorption ability towards HMF molecule leading to more favourable oxidation of HMF. Post characterizations demonstrated pristine Co_(3)O_(4) structure was kept after electrolysis cycles and CoOOH active species were formed. This work provides a valuable reference for developing efficient heteroatom-doped electrocatalysts for HMF oxidation.

Pd-catalyzed asymmetric carbonyl alkynylation:Synthesis of axial chiral ynones

Ynones are important skeletons in bioactive molecules and valuable building blocks for organic synthesis,thus great efforts have been devoted to their preparation.While,introducing prochiral substrates to construct ynones bearing a chiral framework is unrealized to date.Herein,we reported the first example of Pd/SOP-catalyzed asymmetric carbonylative alkynylation via a non-classical carbonylative Sonogashiratype approach(acyl-Pd(Ⅱ)species generated from nucleophiles).By using cyclic diaryliodonium salts as prochiral substrates,various axial chiral ynones with good functional group tolerance(39 examples),satisfied yields(71%-96%)and excellent enantioselectivities(generally 94%-99%ee)were produced.Synthesis of bioactive compounds,scale-up experiment and useful transformations were also conducted to demonstrate the utility of this process.

Degradation of carbamazepine by MWCNTs-promoted generation of high-valent iron-oxo species in a mild system with O-bridged iron perfluorophthalocyanine dimers

Metal phthalocyanine has been extensively studied as a catalyst for degradation of carbamazepine(CBZ).However,metal phthalocyanine tends to undergo their own dimerization or polymerization,thereby reducing their activity points and affecting their catalytic properties.In this study,a catalytic system consisting of O-bridged iron perfluorophthalocyanine dimers(FePcF16-O-FePcF16),multi-walled carbon nanotubes(MWCNTs)and H2O_(2) was proposed.The results showed MWCNTs loaded with FePcF16-O-FePcF16 can achieve excellent degradation of CBZ with smaller dosages of FePcF16-O-FePcF16 and H2O_(2),and milder reaction temperatures.In addition,the results of experiments revealed the reaction mechanism of non-hydroxyl radicals.The highly oxidized high-valent iron-oxo(Fe(IV)=O)species was the main reactive species in the FePcF16-O-FePcF16/MWCNTs/H2O_(2) system.It is noteworthy that MWCNTs can improve the dispersion of FePcF16-O-FePcF16,contributing to the production of highly oxidized Fe(IV)=O.Then,the pathway of CBZ oxidative degradation was speculated,and the study results also provide new ideas for metal phthalocyanine-loaded carbon materials to degrade emerging pollutants.

A study on singlet oxygen generation for tetracycline degradation via modulating the size ofα-Fe_(2)O_(3)nanoparticle anchored on g-C_(3)N_(4) nanotube photocatalyst

Photocatalysis is considered as an effective technique for mitigating ecological risks posed by residual tetracycline(TC).To improve the efficiency of this technique,it is necessary to enable photocatalysts to produce highly reactive species,such as singlet oxygen(1O2).However,due to the high activation energy of 1O2,photocatalysts can hardly produce 1O2 without assistance from external oxidants.Herein,we find that the size-reducedα-Fe_(2)O_(3)nanoparticles(~4 nm)that anchored on g-C_(3)N_(4)nanotube(α-Fe_(2)O_(3)@CNNT)can spontaneously generate ^(1)O_(2) for degradation of TC.In comparison,only hydroxyl radical(·OH)can be produced by g-C_(3)N_(4)nanotube loaded with~14 nmα-Fe_(2)O_(3)nanoparticles(α-Fe_(2)O_(3)/CNNT).Owing to the high reactivity of the ^(1)O_(2) species,the photocatalytic degradation rate(Kapp)of TC withα-Fe_(2)O_(3)@CNNT(0.056 min^(−1))was 1.8 times higher than that ofα-Fe_(2)O_(3)/CNNT.The experimental results and theoretical calculations suggested that reducing the size ofα-Fe_(2)O_(3)nanoparticles anchored on g-C_(3)N_(4)nanotube decreased the surface electron density ofα-Fe_(2)O_(3),which induces the generation of high-valent Fe(IV)active sites overα-Fe_(2)O_(3)@CNNT and turns the degradation pathway into a unique ^(1)O_(2) dominated process.This study provides a new insight on the generation of ^(1)O_(2) for effective degradation of environmental pollutant.

MIL-125(Ti)中引入高价态钨元素以促进光催化产氢性能

金属有机框架(Metal-organic frameworks, MOFs)材料具有高度可调控的多孔结构以及电子结构,在光催化领域非常有前景.本文利用MOFs的上述特性,将高价态的钨元素连接在MIL-125(Ti)中的Ti-oxo团簇上,得到了W-MIL-125.形成的W–O–Ti结构引发了从金属到团簇的电荷传输(Metal-to-cluster charge transfer, MCCT),且W-MIL-125具有更好的吸光性能.结构和谱学表征证明, MCCT过程能优化电荷的传输路径,有效地实现了载流子空间分离. W-MIL-125在光照条件下展现出更高的产氢性能,高达1110.7±63.7μmol g^(-1)h^(-1),是本体样品产氢速率的4.0倍.本工作为MOFs基材料的局域结构改性以提升光催化性能提供了新的思路.

High‑Valence Transition Metal Modified FeNiV Oxides Anchored on Carbon Fiber Cloth for Efficient Oxygen Evolution Catalysis

Developing efficient and durable non-noble metal-based oxygen evolution catalysts is of great importance for electrochemical water splitting.Here,we report a new and facile strategy for controllable synthesis of high-valence Mo modified FeNiV oxides as efficient OER catalysts.The Mo-dopant displays a significant influence on the valence state of Fe species in the catalysts,which lead to tunable OER performance.When the feed ratio of Mo-dopant is 5%,the Mo-modified FeNiV oxide shows the best OER performance in terms of low overpotential(237 mV at the current density of 10 mA cm^(−2)),Tafel slope(38 mV per decade),and high mass activity,which exceeds its counterparts and most reported OER catalysts.Furthermore,by assembling the catalyst with a carbon fiber cloth,the fabricated water-splitting device exhibits excellent activity and longterm durability in alkaline electrolyte compared with commercial catalysts equipped device.This work not only provides a series of Mo-modified FeNiV-based oxides as high-performance OER catalysts but also offers a new pathway to tune the charge states of OER active centers.

Product identification and toxicity change during oxidation of methotrexate by ferrate and permanganate in water

Accompanying an annual increase in cancer incidence,the global use of anticancer drugs has remarkably increased with their worldwide environmental prevalence and ecological risks.In this study,the oxidation of methotrexate(MTX),a typical anticancer drug with ubiquitous occurrence and multi-endpoint toxicity,by ferrate(VI)(Fe(VI))and permanganate(Mn(VII)))was investigated in water.Fe(VI)exhibited a higher reactivity with MTX(93.34 M^(−1) s^(−1))than Mn(VII)(3.01 M^(−1) s^(−1)) at pH 8.0.The introduction of Cu(II)and Fe(III)at 1.0 mM improved the removal efficiency of 5.0μM MTX by 100.0μM Fe(VI)from 80%to 95%and 100%after 4 min,respectively.Seven oxidized products(OPs)were identified during oxidative treatments,while OP-191 and OP-205 were characterized as specific products for Fe(VI)oxidation.Initial ketonization of the L-glutamic acid moiety and cleavage of the peptide bond of MTX were proposed.Additionally,a multi-endpoint toxicity evaluation indicated no genotoxicity,neurotoxicity,or endocrine-disrupting effects of MTX and its OPs.Particularly,serious developmental toxicity in zebrafish larvae was observed in the treated MTX solutions.Based on the acute and chronic aquatic toxicity prediction,OP-190,OP-192,OP-206,and OP-208 were deemed toxic or very toxic compared to harmful MTX.Furthermore,the reduced biodegradability index from 0.15(MTX)to−0.5 to−0.2(OP-192,OP-206,and OP-468)indicated the formation of lower biodegradable OPs.Overall,this study suggests that Fe(VI)and Mn(VII)oxidation are promising treatments for remediating anticancer drug-contaminated water.However,the environmental risks associated with these treatments should be considered in the evaluation of water safety.