Oxygen Reduction Catalysis Research Articles

Comparative Studies of g-C3N4 and C3N3S3 Organic Semiconductors-Synthesis, Properties, and Application in the Catalytic Oxygen Reduction.

Exfoliated g-C3N4 is a well-known semiconductor utilized in heterogenous photocatalysis and water splitting. An improvement in light harvesting and separation of photogenerated charge carriers may be obtained by polymer doping with sulfur. In this work, we incorporate sulfur into the polymer chain by chemical polymerization of trithiocyanuric acid (C3N3S3H3) to obtain C3N3S3. The XRD measurements and TEM images indicated that C3N3S3, in contrast to g-C3N4, does not exist in the form of a graphitic structure and is not exfoliated into thin lamellas. However, both polymers have similar optical properties and positions of the conduction and valence bands. The comparative studies of electrochemical oxygen reduction and hydrogen evolution indicated that the overpotentials for the two processes were smaller for C3N3S3 than for g-C3N4. The RDE experiments in the oxygen-saturated solutions of 0.1 M NaOH have shown that O2 is electrochemically reduced via the serial pathway with two electrons involved in the first step. The spectroscopic experiments using NBT demonstrated that both polymers reveal high activity in the photocatalytic reduction of oxygen to superoxide anion radical by the photogenerated electrons.

Effects of support material and electrolyte on a triphenylamine substituted cobalt porphyrin catalytic oxygen reduction reaction

The interfacial charge transfer conditions are crucial for understanding the catalytic mechanism and thus developing high performing electrocatalysts. To justify the effects of support material and electrolyte on metalloporphyrin catalytic oxygen reduction reaction (ORR), we synthesize a symmetric triphenylamine (TPA) substituted cobalt porphyrin, nominated as s-TPA-CoP, and select carbon black and multi-walled carbon nanotubes as the supports to fabricate composite catalysts. The ORR performances are measured in both acidic and alkaline solutions. While the support material affects negligibly on reduction potentials, the stronger π-π stacking in s-TPA-CoP/CNT, as revealed by X-ray photoelectron spectroscopy measurements, leads to greater limiting current densities and larger electron transfer numbers as compared to s-TPA-CoP/XC in either electrolyte. Both composites perform better ORR activity but poorer 4-electron selectivity in base than in acid, whose origins are discussed from the aspects of interfacial charge states and inner- / outer-sphere electron transfer mechanisms. Strikingly, s-TPA-CoP/CNT exhibits an electron transfer number of 3.8 in acid, demonstrating the privilege of TPA as the substitution on monometallic cobalt porphyrins in chasing 4-electron transfer oxygen reduction.

Molecular Insights into the Structure-Activity Relationship in Cobalt Porphyrin Catalyzed Oxygen Reduction Reaction

Molecular Insights into the Structure-Activity Relationship in Cobalt Porphyrin Catalyzed Oxygen Reduction Reaction

Modeling Anion Poisoning during Oxygen Reduction on Pt Near-Surface Alloys

Electrolyte effects play an important role in the activity of the oxygen reduction reaction (ORR) of Pt-based electrodes. Herein, we combine a computational model and rotating disk electrode measurements to investigate the effects from phosphate anion poisoning for the ORR on well-defined extended Pt surfaces. We construct a model including the poisoning effect from phosphate species on Pt(111) and Cu/Pt(111) based on density functional theory simulations. By varying the subsurface Cu content of the Cu/Pt(111) alloy, we tune the *OH binding energies on the surface by means of ligand effects, and as a result, we tune the ORR activity. We have investigated the effect of adsorbed phosphate species at low overpotentials when tuning *OH binding energies. Our results display a direct scaling relationship between adsorbed *OH and phosphate species. From the model, we observe how the three-fold binding sites of phosphate anions limit the packing of poisoning phosphate on the surface, thus allowing for *OH adsorption even when poisoned. Our work shows that, regardless of surface site blockage from phosphate, the trend in the catalytic oxygen reduction activity is predominantly governed by the *OH binding.

Vapor expansion growth of core–shell Cu O C catalysts to boost low temperature oxygen reduction catalysis

Vapor expansion growth of core–shell Cu O C catalysts to boost low temperature oxygen reduction catalysis

A pathway for promoting bioelectrochemical performance of microbial fuel cell by synthesizing graphite carbon nitride doped on single atom catalyst copper as cathode catalyst

In this study, a simple distributed feeding method was used to dope graphite phase carbon nitride (g-C3N4) on single atom catalyst (SAC) copper (Cu) to form composite material (Cu-SA/CN). Cu-SA/CN was formed by mutual doping of polyhedral block Cu and irregular g-C3N4. There were obvious crystal face peaks at 28.4, 43.3, 47.3 and 56.2°. Large solid Cu and small irregular g-C3N4 were successfully combined and C, Cu, N and O elements were uniformly distributed on the surface of Cu-SA/CN. The valence bond of N-CN, C-NC, CC and OH was found. When the Cu content was 0.03 mol, Cu-SA/CN3 showed excellent redox activity. The maximum power density of Cu-SA/CN3-MFC was 456.976 mW/m2, the maximum voltage was 599 mV, which could be stable for 7 d. Cu-SA/CN3 was proved to provide more electrically active sites, strong catalytic oxygen reduction ability and conductivity.

Three birds with one stone: Contemporaneously boosting passive, active and self-healing properties for long-term anticorrosion coatings

Stimuli-responsive coatings can self-repair their own anticorrosion function in response to environmental changes, but they do not exhibit ideal long-term protective effect due to the lack of ability to regulate corrosive media, while this is vital to practical metal protection. Inspired by catalytic oxygen reduction, Cu-N center doped graphene oxide grafted with hollow periodic mesoporous organosilica nanocontainer (MBT@HPMO/Cu-GO) is synthesized via facile adsorption-pyrolysis strategy. Herein, introduced MBT@HPMO/Cu-GO is to simultaneously endow coatings with corrosive media shielding, active oxygen consumption and stimuli-responsive functions, thus “three birds with one stone”. The target catalyst exhibits excellent oxygen depletion performance (half-wave potential of 0.85 V) and is uniformly dispersed in the coating to construct steric hindrance against corrosive media. This dual effect allows composite coating to maintain the excellent anticorrosion performance over 60 days under oxygen environment. In addition, MBT@HPMO/Cu-GO can release inhibitor at corrosion sites in response to environment change when coating is damaged, so as to restore the protective ability of coating, with impedance increased from 2.4 × 107 Ω·cm2 to 1.5 × 108 Ω·cm2. Such multifunctional coating exploration overcomes the protective limitation of current self-healing coatings and sheds light on the design of intelligent long-term anticorrosion coatings.

Immobilization of Platinum Nanoparticles on Covalent Organic Framework‐Derived Carbon for Oxygen Reduction Catalysis

Platinum (Pt)‐based catalysts are considered as the most active catalysts for the oxygen reduction reaction (ORR). However, their applications have remained limited because of the high cost of Pt, and developing catalysts with low Pt contents is a challenge. Herein, a highly active catalyst (Pt–COF800) is constructed for the ORR by immobilizing hierarchical Pt subnano‐ and nanoparticles on covalent organic framework (COF)‐derived carbon. The catalyst shows excellent activity in alkaline conditions. The physical characterization demonstrates low nuclear Pt atoms and nanoparticles and confirms the role of heterogeneous active sites. This work paves the way for the construction of functional porous carbon materials with dual‐scale Pt clusters and may be applied to industrial catalytic reactions.

The synergistic effect of “soft-hard template” to in situ regulate mass transfer and defective sites of doped-carbon nanostructures for catalysis of oxygen reduction

Nitrogen-doped carbon materials are intensively investigated as electrocatalysts toward oxygen reduction reaction (ORR). The activity of the catalysts can be effectively boosted by regulating the microstructure to construct defective three-phase interface. Herein, an N-doped carbon-based porous catalyst (DT-Fe-N-C) is fabricated by a dual-template strategy with SiO2 and pluronic F127 as the hard and soft templates. Benefited from the modulation, the mesopore-dominated DT-Fe-N-C exhibits remarkable specific surface area (990.19 m2 g-1), high Fe-Nx content and plenty of defects. Resultantly, DT-Fe-N-C shows outstanding catalytic activity to ORR with 0.853 V of half-wave potential, high stability and selectivity to the four-electron ORR mechanism. The Zn-air battery with DT-Fe-N-C outputs 219 mW cm-2 of maximum power density, 861 Wh kgZn−1 of specific energy density at 50 mA cm-2 and runs at a higher voltage than that of Pt/C-based battery. This work provides an avenue for the defect engineering in the design of non-precious metal ORR catalysts.

Metal organic polymers with dual catalytic sites for oxygen reduction and oxygen evolution reactions

AbstractMetal–organic frameworks and covalent organic frameworks have been widely employed in electrochemical catalysis owing to their designable skeletons, controllable porosities, and well‐defined catalytic centers. However, the poor chemical stability and low electron conductivity limited their activity, and single‐functional sites in these frameworks hindered them to show multifunctional roles in catalytic systems. Herein, we have constructed novel metal organic polymers (Co‐HAT‐CN and Ni‐HAT‐CN) with dual catalytic centers (metal–N4 and metal–N2) to catalyze oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). By using different metal centers, the catalytic activity and selectivity were well‐tuned. Among them, Co‐HAT‐CN catalyzed the ORR in a 4e− pathway, with a half‐wave potential of 0.8 V versus RHE, while the Ni‐HAT‐CN catalyze ORR in a 2e− pathway with H2O2 selectivity over 90%. Moreover, the Co‐HAT‐CN delivered an overpotential of 350 mV at 10 mA cm−2 with a corresponding Tafel slope of 24 mV dec−1 for OER in a 1.0 M KOH aqueous solution. The experimental results revealed that the activities toward ORR were due to the M–N4 sites in the frameworks, and both M–N4 and M–N2 sites contributed to the OER. This work gives us a new platform to construct bifunctional catalysts.

Kinetic and mechanistic investigations of dioxygen reduction by a molecular Cu(II) catalyst bearing a pentadentate amidate ligand.

A pentadentate Cu(II) complex, [CuII(dpaq)](ClO4) (1), featuring a redox active ligand, H-dpaq (H-dpaq = 2-[bis(pyridine-2-ylmethyl)]amino-N-quinolin-8-yl-acetamidate), catalyses four-electron reduction of dioxygen by decamethylferrocene (Fc*) in the presence of trifluoroacetic acid (CF3COOH) in acetone at 298 K. No catalytic oxygen reduction was observed in the presence of stronger Brønsted acids than CF3COOH, such as perchloric acid (HClO4) or trifluoromethanesulphonic acid (HOTf). In contrast, facile catalytic reduction of O2 occurs by Fc* with 1 and HClO4 or HOTf in dimethylformamide (DMF). The use of CF3COOH as the proton source in DMF results in the suppression of O2 reduction under otherwise identical reaction conditions. While the O2 reduction reactions in DMF are linearly dependent on the pKa of Brønsted acids, the acid dependence on catalytic O2-reduction reactivity by 1 in acetone showed complete reversal. Cyclic voltammetry studies using p-chloranil as the probe substrates in the presence of acids in the solvents reveal that the strengths of the protonic acids increase significantly in acetone compared to that in DMF. The amidate-N in [CuII(dpaq)](ClO4) (1) undergoes protonation in the presence of HClO4 or HOTf in DMF to form [CuII(H-dpaq)]2+ (1-H+), but not in the presence of CF3COOH. Enhanced acid strength of CF3COOH in acetone, however, effectively protonates 1 and triggers O2 reduction. Protonation of 1 with HClO4 or HOTf in acetone results in the change of its coordination environment, and this protonated species does not trigger O2 reduction. Detailed kinetic studies indicate that 1-H+ undergoes reduction by two-electrons and the reduced species binds O2 to form a Cu(II)-superoxo intermediate. This is followed by a rate-determining proton-coupled electron-transfer (PCET) reduction to generate the Cu(II)-hydroperoxo intermediate. While catalytic O2 reduction in acetone occurs predominantly via a 4e-/4H+ pathway, product selectivity (H2O vs. H2O2) in DMF depends upon the concentration of the reductant (Fc*). While dioxygen reduction to H2O2 is favoured at low [Fc*], mechanistic studies suggest that O2 reduction with high [Fc*] proceeds via a [2e- + 2e-] mechanism, where the released H2O2 during catalysis is further reduced to water.

In situgrowth of Co3O4nanoparticles on nitrogen-doped reduced graphene oxide for high-efficiency oxygen reduction catalysis

Thein situsynthesis of efficient and economical electrocatalysts are pivotal for the oxygen reduction reaction (ORR) process in energy related devices such as fuel cells and metal–air batteries.

Atomically dispersed Mn atoms coordinated with N and O within an N-doped porous carbon framework for boosted oxygen reduction catalysis.

Developing efficient and robust catalysts to replace Pt group metals for the oxygen reduction reaction (ORR) is conducive to achieving highly efficient energy conversion. Here, we develop a general ion exchange strategy to construct highly efficient ORR catalysts consisting of various atomically dispersed metal atoms anchored on N-doped porous carbon (M-SAs/NC) to investigate the atomic structure-catalytic activity relationship. The structure characterization results demonstrated that the achieved atomic structure varied due to the presence of different metal centers. Mn-SAs/NC consists of MnN3O1 centers, in which the Mn single atoms are stabilized by 3 N and 1 O. In contrast, the center metals in Fe-/Co-/Cu single-atom catalysts are coordinated by merely N atoms. Mn-SAs/NC delivers superior performance for the ORR with a half-wave potential (E1/2) of 0.91 V vs. RHE in 0.1 M KOH solution, outperforming that of the commercial Pt/C catalyst and the control Fe-/Co-/Cu single-atom catalysts. Furthermore, Mn-SAs/NC also shows excellent methanol tolerance and stability up to 5000 cycles. Density functional theory (DFT) calculations reveal that Mn single atom catalysts with MnN3O1 centers contributed to the superior ORR performance with lower energy barriers and optimized adsorption capacity of intermediates. These findings provide insights into the design and development of specific coordinated structures of atomically dispersed catalysts to facilitate the practical applications of energy conversion.

Mass production of a dealloyed Pt3Co/C catalyst for oxygen reduction catalysis in PEMFCs

D-Pt3Co/C with remarkable ORR/MEA performances has been prepared on a large scale. This robust method can be readily extended to prepare many ternary, quaternary and quinary Pt3Co-based alloy catalysts, demonstrating great potential in PEMFCs.

Nitrogen-intercalated Pd metallene nanoribbons with optimized electronic structure for oxygen reduction catalysis.

Herein, we propose nitrogen (N)-intercalated Pd metallene nanoribbons (N-Pd MNRs), which exhibit favorable and stable oxygen reduction reaction (ORR) performance in alkaline media. The ultrathin configuration of the N-Pd MNRs exposes more atoms, thus acting as active sites. More importantly, N intercalation triggers electronic interaction between Pd and N to establish Pd-N bonds and induces lattice strain, which optimizes the electronic structure of the metallene nanoribbons, thereby modulating the binding strength between the intermediates and active sites. This work offers new insights into the rational design of N intercalated metallene nanoribbons for efficient ORR catalysis.

Regulating the Electronic Structure of Cu-Nx Active Sites for Efficient and Durable Oxygen Reduction Catalysis to Improve Microbial Fuel Cell Performance.

The efficient and durable oxygen reduction reaction (ORR) catalyst is of great significance to boost power generation and pollutant degradation in microbial fuel cells (MFCs). Although transition metal-nitrogen-codoped carbon materials are an important class of ORR catalysts, copper-nitrogen-codoped carbon is not considered a suitable MFC cathode catalyst due to the insufficient performance and especially instability. Herein, we report a three-dimensional (3D) hierarchical porous copper, nitrogen, and boron codoped carbon (3DHP Cu-N/B-C) catalyst synthesized by the dual template method. The introduced B atom as an electron donor increases the electron density around the Cu-Nx active site, which significantly promotes the efficiency of the ORR process and stabilizes the active site by preventing demetallization. Thus, the 3DHP Cu-N/B-C catalyst exhibited excellent ORR performance with the half-wave potential of 0.83 V (vs reversible hydrogen electrode (RHE)) in a 0.1 M KOH electrolyte and 0.68 V (vs RHE) in a 50 mM PBS electrolyte. Meanwhile, 3DHP Cu-N/B-C had satisfactory stability with 94.16% current retention after 24 h of chronoamperometry test, which is better than that of 20% Pt/C. The MFCs using 3DHP Cu-N/B-C not only showed a maximum power density of up to 760.14 ± 19.03 mW m-2 but also operating durability of more than 50 days. Moreover, the 16S rDNA sequencing results presented that the 3DHP Cu-N/B-C catalyst had a positive effect on the microbial community of the MFC with more anaerobic electroactive bacteria in the anode biofilm and fewer aerobic bacteria in the cathode biofilm. This study provides a new approach for the development of Cu-based ORR electrocatalysts as well as guidance for the rational design of high-performance MFCs.

Evidence of Sulfur Non-Innocence in [CoII (dithiacyclam)]2+ -Mediated Catalytic Oxygen Reduction Reactions.

In many metalloenzymes, sulfur-containing ligands participate in catalytic processes, mainly via the involvement in electron transfer reactions. In a biomimetic approach, we now demonstrate the implication of S-ligation in cobalt mediated oxygen reduction reactions (ORR). A comparative study between the catalytic ORR capabilities of the four-nitrogen bound [Co(cyclam)]2+ (1; cyclam=1,5,8,11-tetraaza-cyclotetradecane) and the S-containing analog [Co(S2 N2 -cyclam)]2+ (2; S2 N2 -cyclam=1,8-dithia-5,11-diaza-cyclotetradecane) reveals improved catalytic performance once the chalcogen is introduced in the Co coordination sphere. Trapping and characterization of the intermediates formed upon dioxygen activation at the CoII centers in 1 and 2 point to the involvement of sulfur in the O2 reduction process as the key for the improved catalytic ORR capabilities of 2.

Beweis von Schwefel‐non‐Innocence in [CoII(Dithiacyclam)]2+‐vermittelten, katalytischen Sauerstoff‐Reduktions‐Reaktionen

AbstractIn vielen Metallenzymen sind Schwefel‐enthaltende Liganden an Elektronen‐Transfer‐Reaktionen beteiligt. In dem hier diskutierten biomimetischen Ansatz wird der Einfluss einer Schwefelkoordination auf eine Kobalt‐katalysierte Sauerstoff‐Reduktionsreaktion (ORR) demonstriert. Ein Vergleich des ORR‐Vermögens eines vierfach Stickstoff‐koordinierten [Co(Cyclam]2+‐Komplexes (1; Cyclam=1,5,8,11‐Tetraaza‐cyclotetradecan) und dessen Schwefel‐Analogons [Co(S2N2‐Cyclam)]2+(2; S2N2‐Cyclam=1,8‐Dithia‐5,11‐diazacyclotetradecan) zeigt verbesserte katalytische Eigenschaften mit dem in die Ligandensphäre am Kobalt eingeführten Chalkogen. Isolierung und Charakterisierung der Intermediate, die sich im Zuge der Sauerstoffaktivierung an den Kobalt(II)‐Zentren von1und2bilden, identifizieren eine Beteiligung des Schwefels am O2‐Reduktionsprozess als entscheidenden Faktor für die verbesserten Eigenschaften von2bei der katalytischen ORR.

Enhanced bioelectrochemical performance by NiCoAl-LDH/MXene hybrid as cathode catalyst for microbial fuel cell

In this work, NiCoAl-layered double hydroxide (LDH)/MXene was successfully prepared through straightforward hydrothermal method. NiCoAl-LDH was tightly and uniformly coated on MXene, forming a kind of porous structure. NiCoAl-LDH/MXene exhibited the (002) (012) (105) (100) crystal planes of hydrotalcite reflection. NiCoAl-LDH/MXene also showed superior catalytic oxygen reduction reaction (ORR) in response current according to electrochemical test (cyclic voltammetry (CV) etc.). The maximum power density and output voltage of NiCoAl-LDH/MXene as cathode in microbial fuel cell (MFC) was 362.404 mW/m2 and 450 mV, respectively, which was 1.54 times of MXene-MFC (234.256 mW/m2) and 1.71 times of NiCoAl-LDH-MFC (211.56 mW/m2). The results indicated that NiCoAl-LDH/MXene was a kind of potential cathode catalyst for MFC and was full of future application.

Continuous Production of Carbon-Supported and Surfactant-Free Pt-M (M=Fe, Co, Ni, and Cu) Nanocrystals for Catalyzing Oxygen Reduction

Scalable production of carbon-supported Pt-M (M=Co, Ni, and Fe) alloy nanocrystals is of great importance for their practical application as catalysts towards the oxygen reduction reaction (ORR), a process key to the operation of proton-exchange membrane fuel cells. Here we report the use of a fluidic device for the in situ nucleation and growth of Pt-M nanocrystals on a commercial carbon support in a continuous and scalable fashion. The use of dimethylformamide not only enables well dispersion of the carbon powders for the creation of a homogeneous reaction mixture but also helps reduce metal precursors for the heterogeneous nucleation and growth of nanocrystals on the carbon surface. The size, shape, and composition of the nanocrystals can all be tuned by changing the metal precursors added into the reaction mixture, resulting in Pt-M nanocrystals uniformly distributed across the surface of the carbon support. Among the nanocrystals, the carbon-supported Pt-Co nanocrystals show the highest ORR specific and mass activities at 0.9 V, demonstrating 11.4- and 8.8-fold enhancements over the state-of-the-art commercial Pt/C catalyst.