RESUMEN

Understanding the spin-dependent activity of nitrogen-coordinated single metal atom (M-N-C) electrocatalysts for oxygen reduction and evolution reactions (ORR and OER) remains challenging due to the lack of structure-defined catalysts and effective spin manipulation tools. Herein, both challenges using a magnetic field integrated heterogeneous molecular electrocatalyst prepared by anchoring cobalt phthalocyanine (CoPc) deposited carbon black on polymer-protected magnet nanoparticles, are addressed. The built-in magnetic field can shift the Co center from low- to high-spin (HS) state without atomic structure modification, affording one-order higher turnover frequency, a 50% increased H2O2 selectivity for ORR, and a ≈4000% magnetocurrent enhancement for OER. This catalyst can significantly minimize magnet usage, enabling safe and continuous production of a pure H2O2 solution for 100 h from a 100 cm2 electrolyzer. The new strategy demonstrated here also applies to other metal phthalocyanine-based catalysts, offering a universal platform for studying spin-related electrochemical processes.

RESUMEN

In the pursuit of optimizing Fe-N-C catalysts for the oxygen reduction reaction (ORR), the incorporation of alloy nanoparticles has emerged as a prominent strategy. In this work, we effectively synthesized the FeRu-NC catalyst by anchoring Fe-Ru alloy nanoparticles and FeN4 single atom sites onto carbon nanotubes. The FeRu-NC catalyst exhibits significantly enhanced ORR activity and long-term stability, with a high half-wave potential of 0.89 V (vs. RHE) in alkaline conditions, and the half-wave potential remains nearly unchanged after 5000 cycles. The zinc-air battery (ZAB) assembled with FeRu-NC demonstrates a power density of 169.1 mW cm-2, surpassing that of commercial Pt/C. Density functional theory (DFT) calculations reveal that the synergistic interaction between the Fe-Ru alloy and FeN4 single atoms alters the electronic structure and facilitates charge transfer at the FeN4 sites, thereby modulating the adsorption and desorption of ORR intermediates. This enhancement in catalytic activity for the ORR process underscores the potential of this approach for refining M-N-C catalysts, providing novel insights into their optimization strategies.

RESUMEN

Cytochrome c oxidase (CcO) is the terminal enzyme in the electron transfer chain in mitochondria. It catalyzes the four-electron reduction of O2 to H2O and harnesses the redox energy to drive unidirectional proton translocation against a proton electrochemical gradient. A great deal of research has been conducted to comprehend the molecular properties of CcO. However, the mechanism by which the oxygen reduction reaction is coupled to proton translocation remains poorly understood. Here, we review the chemical properties of a variety of key oxygen intermediates of bovine CcO (bCcO) revealed by time-resolved resonance Raman spectroscopy and the structural features of the enzyme uncovered by serial femtosecond crystallography, an innovative technique that allows structural determination at room temperature without radiation damage. The implications of these data on the proton translocation mechanism are discussed.

RESUMEN

Protonic ceramic electrochemical cells (PCECs) have demonstrated great promise for applications in the generation of electricity, and the synthesis of chemicals (for example, ethylene). However, enhancing the electrochemical reactions kinetics and stability of PCECs electrodes is one grand challenge. Here, we present a novel electrode material via a co-doping of cesium (Cs) and niobium (Nb) on PrBaCo2O6-δ with the composition of PrBa0.9Cs0.1Co1.9Nb0.1O6-δ (PBCCN), which naturally decomposes into dual phases of a double-perovskite PBCCN (DP-PBCCN, ∼92.3 wt%) and a single-perovskite Ba0.9Cs0.1Co0.95Nb0.05O3-δ (SP-BCCN, ∼7.7 wt%) under typical powder processing conditions. PBCCN exhibits a low area-specific resistance (ASR) value of 0.107 Ω cm2, an outstanding performance of 2.04 W cm-2 in fuel cell (FC) mode, a current density of -2.84 A cm-2 at 1.3 V in electrolysis cell (EC) mode, and promising reversible operational durability of 53 cycles in ∼212 h at +/- 0.5 A cm-2 and 650 °C. Cs doping generates more oxygen vacancies and accelerates the oxygen exchange kinetics, while Nb doping effectively enhances the stability, as illustrated by the analyses of X-ray photoelectron spectroscopy, and electrical conductivity relaxations. When applied as the positrode for electrochemical non-oxidative dehydrogenation of ethane (C2H6) to ethylene (C2H4) on PCECs, it displays an encouraging C2H6 conversion of 12.75% and a C2H4 selectivity of 98.4% at 1.2 V.

RESUMEN

We present a molecular-scale investigation of the axial coordination effect of atomic iodine on Fe-N4 sites in the oxygen reduction reaction (ORR) by electrochemical scanning tunneling microscopy (ECSTM). A well-defined model catalytic system with explicit and uniform iodine-coordinated Fe-N4 sites was constructed facilely by the self-assembly of iron(II) phthalocyanine (FePc) on an I-modified Au(111) surface. The electrocatalytic activity of FePc for the ORR shows a tremendous enhancement with axial iodine ligands. The ingenious modulation of the electronic structure of Fe sites to evoke a higher spin configuration by axial iodine was evidenced. In addition, the interaction strength between reactive oxygen species and active centers becomes weaker due to the presence of iodine ligands, and the reaction is thermodynamically preferable. Moreover, the facilitated reaction dynamics of FePc on I/Au(111) were explicitly determined via in-situ ECSTM potential pulse experiments. Noteworthily, axial atomic iodine was found inefficacious for improving the activity of Co-N4 sites, and electron rearrangement was not detected, demonstrating that adequate interactions between axial ligands and metal sites for optimizing electronic structures and catalytic behaviors are prerequisites for the impactful role of axial ligands.

RESUMEN

The key to heterogeneous photo-Fenton technology lies in the efficient generation of hydrogen peroxide (H2O2). Herein, a newly-designed ZnO/ZnIn2S4 composite with heterostructure is synthesized. Benefiting from the formation of built-in electric field, the recombination of photoinduced electrons and holes is suppressed and interfacial charge transfer resistance is reduced. Importantly, the embedding of ZnO in ZnIn2S4 can improve the hydrophobicity and create microscopic three-phase interface, thereby boosting the capture capability for O2 and providing the convenience for the occurrence of O2 reduction reaction. More interestingly, the existence of ZnIn2S4 in the ZnO/ZnIn2S4 composite can reduce the Gibbs free energy (ΔG) of key intermediate (OOH*) formation, which will accelerate the generation of H2O2. As a result, the ZnO/ZnIn2S4 composite displays excellent performance in photocatalytic H2O2 production, and the highest yield was about 897.6 µmol/g/h within 60 min under visible light irradiation. The transfer of photoinduced carriers follows the S-scheme type mechanism. The photogenerated holes can be captured by drug residues (i.e., diclofenac sodium) to accelerate H2O2 production, while generated H2O2 can combine with Fe2+ to construct photo-Fenton system for achieving the advanced degradation of diclofenac sodium, which was mainly related to the formation of OH•. Furthermore, generated H2O2 can be applied for performing the inactivation of pathogenic bacteria. In short, current work will provide a valuable reference for future research.

Asunto(s)

RESUMEN

Understanding the structure evolution, kinetics, and mass transfer for the oxygen reduction reaction (ORR) at the ionomer-catalyst interface is fundamental for the development of anion exchange membrane fuel cells (AEMFCs). Herein, we investigate the structural evolution of ionomer-Pt interfaces during the activation process of polycrystalline Pt (poly-Pt) electrodes and their ORR kinetics and mass transfer characteristics at steady state. The results suggest the ionomer thickness as a critical factor in determining the Pt surface structure and the flux of the O2 diffusion, which in turn affect the subsequent kinetic and mass transfer of the ORR on ionomer-Pt electrode interfaces. Thicker ionomer film leads to a more severe evolution of electrochemical features during the activation process, likely caused by forming more less-active Pt clusters at the ionomer-Pt interface. Thus, the ORR kinetic activity at the steady state decreases with the increase in ionomer thickness. Concurrently, the thicker ionomer leads to a reduced diffusion flux of O2, culminating in a lower limiting current density for the ORR. Additionally, we calculated the diffusion coefficient and solubility of O2 within the FAA-3 alkaline ionomer film, with a comparative assessment against those in the proton exchange membrane (PEM). These findings offer valuable insights into the ionomer-Pt interface in AEMFCs and their effects on performance.

RESUMEN

Dual-atom catalysts (DACs) have garnered significant interest due to their remarkable catalytic reactivity. However, achieving atomically precise control in the fabrication of DACs remains a major challenge. Herein, we developed a straightforward and direct sublimation transformation synthesis strategy for dual-atom Fe catalysts (Fe2/NC) by utilizing in situ generated Fe2Cl6(g) dimers from FeCl3(s). The structure of Fe2/NC was investigated by aberration-corrected transmission electron microscopy and X-ray absorption fine structure (XAFS) spectroscopy. As-obtained Fe2/NC, with a Fe-Fe distance of 0.3 nm inherited from Fe2Cl6, displayed superior oxygen reduction performance with a half-wave potential of 0.90 V (vs. RHE), surpassing commercial Pt/C catalysts, Fe single-atom catalyst (Fe1/NC), and its counterpart with a common and shorter Fe-Fe distance of ~0.25 nm (Fe2/NC-S). Density functional theory (DFT) calculations and microkinetic analysis revealed the extended Fe-Fe distance in Fe2/NC is crucial for the O2 adsorption on catalytic sites and facilitating the subsequent protonation process, thereby boosting catalytic performance. This work not only introduces a new approach for fabricating atomically precise DACs, but also offers a deeper understanding of the intermetallic distance effect on dual-site catalysis.

RESUMEN

Defect engineering is an effective strategy for regulating the electrocatalysis of nanomaterials, yet it is seldom considered for modulating Pt-based electrocatalysts for the oxygen reduction reaction (ORR). In this study, we designed Ni-doped vacancy-rich Pt nanoparticles anchored on nitrogen-doped graphene (Vac-NiPt NPs/NG) with a low Pt loading of 3.5 wt.% and a Ni/Pt ratio of 0.038:1. Physical characterizations confirmed the presence of abundant atomic-scale vacancies in the Pt NPs induces long-range lattice distortions, and the Ni dopant generates a ligand effect resulting in electronic transfer from Ni to Pt. Experimental results and theoretical calculations indicated that atomic-scale vacancies mainly contributed the tolerance performances towards CO and CH3OH, the ligand effect derived from a tiny of Ni dopant accelerated the transformation from *O to *OH species, thereby improved the ORR activity without compromising the tolerance capabilities. Benefiting from the synergistic interplay between atomic-scale vacancies and ligand effect, as-prepared Vac-NiPt NPs/NG exhibited improved ORR activity, sufficient tolerance capabilities, and excellent durability. This study offers a new avenue for modulating the electrocatalytic activity of metal-based nanomaterials.

RESUMEN

Electro-oxidation (EO) technology demonstrates significant potential in wastewater treatment. However, the high energy consumption has become a pivotal constraint hindering its large-scale implementation. Herein, we design an EO and 4-electron oxygen reduction reaction coupled system (EO-4eORR) to replace the traditional EO and hydrogen evolution reaction (HER) coupled system (EO-HER). The theoretical cathodic potential of the electrolytic reactor is tuned from 0 V (vs. RHE) in HER to 1.23 V (vs. RHE) in 4eORR, which greatly decreases the required operation voltage of the reactor. Moreover, we demonstrate that convection can improve the mass transfer of oxygen and organic pollutants in the reaction system, leading to low cathodic polarization and high pollutant removal rate. Compared with traditional EO-HER system, the energy consumption of the EO-4eORR system under air aeration for 95% total organic carbon (TOC) removal is greatly decreased to 2.61 kWh/kgTOC (only consider the electrolyzer energy consumption), which is superior to previously reported EO-based water treatment systems. The reported results in this study offer a new technical mode for development of highly efficient and sustainable EO-based treatment systems to remove organic pollutants in waste water.

RESUMEN

Here Fe2O(SeO3)2/Fe3C@NC catalysts with high performance were fabricated for zinc-air batteries (ZABs). The experimental results confirmed that the existence of Fe-O-Se bonds in Fe2O(SeO3)2 crystal phase, and the Fe-O-Se bonds could obviously enhance ORR and OER catalytic performance of Fe2O(SeO3)2/Fe3C@NC. Density functional theoretical calculations (DFT) confirmed that the Fe2O(SeO3)2 in Fe2O(SeO3)2/Fe3C@NC had a higher d-band center of Fe atom and a lower p-orbital coupling degree with its own lattice O atom than Fe2O3, which leads to Fe site of Fe2O(SeO3)2 being more likely to adsorb external oxygen intermediates. The Fe-O-Se bonds in Fe2O(SeO3)2 results in the modification of coordination environment of Fe atoms and optimizes the adsorption energy of Fe site for oxygen intermediates. Compared with Fe2O3/Fe3C@NC, the Fe2O(SeO3)2/Fe3C@NC showed obvious enhancements of ORR/OER catalytic activities with a half-wave potential of 0.91 V for ORR in 0.1 M KOH electrolyte and a low overpotential of 345 mV for OER at 10 mA cm-2 in a 1.0 M KOH electrolyte. The peak power density and specific capacity of Fe2O(SeO3)2/Fe3C@NC-based ZABs are higher than those of Pt/C+RuO2-ZABs. The above results demonstrate that the asymmetrical Fe-O-Se bonds in Fe2O(SeO3)2 plays a key role in improving the bifunctional catalytic activities of ORR/OER for ZABs.

RESUMEN

Producing H2O2 through a selective, two-electron (2e) oxygen reduction reaction (ORR) is challenging, especially when it serves as an advanced oxidation process (AOP) for cost-effective water decontamination. Herein, we attain a 2e-selectivity H2O2 production using a carbon nanotube electrified membrane with ibuprofen (IBU) molecules laden (IBU@CNT-EM) in an ultrafast, single-pass electrofiltration process. The IBU@CNT-EM can generate H2O2 at a rate of 25.62 mol gCNT-1 h-1 L-1 in the permeate with a residence time of 1.81 s. We demonstrated that an interwoven, hydrophilic-hydrophobic membrane nanostructure offers an excellent air-to-water transport platform for ORR acceleration. The electron transfer number of the ORR for IBU@CNT at neutral pH was confirmed as 2.71, elucidating a near-2e selectivity to H2O2. Density functional theory (DFT) studies validated an exceptional charge distribution of the IBU@CNT for the O2 adsorption. The adsorption energies of the O2 and *OOH intermediates are proportional to the H2O2 selectivity (64.39%), higher than that of the CNT (37.81%). With the simple and durable production of H2O2 by IBU@CNT-EM electrofiltration, the permeate can actuate Fenton oxidation to efficiently decompose emerging pollutants and inactivate bacteria. Our study introduces a new paradigm for developing high-performance H2O2-production membranes for water treatment by reusing environmental functional materials.

RESUMEN

Single atom catalysts (SACs) are promising non-precious catalysts for oxygen reduction reaction (ORR). Unfortunately, the ORR SACs usually suffer from unsatisfactory activity and in particular poor stability. Herein, we report atomically dispersed manganese (Mn) embedded on nitrogen and sulfur co-doped graphene as an efficient and robust electrocatalyst for ORR in alkaline electrolyte, realizing a half-wave potential (E1/2) of 0.883 V vs. reversible hydrogen electrode (RHE) with negligible activity degradation after 40,000 cyclic voltammetry (CV) cycles in 0.1 M KOH. Introducing sulfur (S) to form Mn-S coordination changes the spin state of single Mn atom from high-spin to low-spin, which effectively optimizes the oxygen intermediates adsorption over the single Mn atomic sites and thus greatly improves the ORR activity.

RESUMEN

Forced-flow atomic layer deposition nanolamination is employed to fabricate Pt-Ni nanoparticles on XC-72, with the compositions ranging from Pt94Ni6 to Pt67Ni33. Hydrogen is used as a co-reactant for depositing Pt and Ni. The growth rate of Pt is slower than that using oxygen reactant, and the growth exhibits preferred orientation along the (111) plane. Ni shows much slower growth rate than Pt, and it is only selectively deposited on Pt, not on the substrate. Higher ratios of Ni would hinder subsequent stacking of Pt atoms, resulting in lower overall growth rate and smaller particles (1.3-2.1 nm). Alloying of Pt with Ni causes shifted lattice that leads to larger lattice parameter and d-spacing as Ni fraction increases. From the electronic state analysis, Pt 4f peaks are shifted to lower binding energies with increasing the Ni content, suggesting charge transfer from Ni to Pt. Schematic of the growth behavior is proposed. Most of the alloy nanoparticles exhibit higher electrochemical surface area and oxygen reduction reaction activity than those of commercial Pt. Especially, Pt83Ni17 and Pt87Ni13 show excellent mass activities of 0.76 and 0.59 A mgPt -1, respectively, higher than the DOE target of 2025, 0.44 A mgPt -1.

RESUMEN

The structural tailoring of Pt-based catalysts into 1D nanowires for oxygen reduction reactions (ORR) has been a focus of research. Mo(CO)6 is commonly used as a morphological modifier to form nanowires, but it is found that it inevitably leads to Mo doping. This doping introduces unique electrochemical signals not seen in other Pt-based catalysts, which can directly reflect the stability of the catalyst. Through experiments, it is demonstrated that Mo doping is detrimental to ORR performance, and theoretical calculations have shown that Mo sites that are inherently inactive also poison the ORR activity of the surrounding Pt. Therefore, a novel gas-assisted technique is proposed to replace Mo(CO)6 with CO, which forms ultrafine nanowires with an order of magnitude increase in length, ruling out the effect of Mo. The catalyst performs at 1.24 A mgPt -1, 7.45 times greater than Pt/C, demonstrating significant ORR mass activity, and a substantial improvement in stability. The proton exchange membrane fuel cell using this catalyst provides a higher power density (0.7 W cm-2). This study presents a new method for the preparation of ultra-long nanowires, which opens up new avenues for future practical applications of low-Pt catalysts in PEMFC.

RESUMEN

Pt-based alloy with high mass activity and durability is highly desired for proton exchange membrane fuel cells, yet a great challenge remains due to the high mass transport resistance near catalysts with lowering Pt loading. Herein, an extensible approach employing atomic layer deposition to accurately introduce a gas-phase metal precursor into platinum nanoparticles (NPs) pre-filled mesoporous channels is reported, achieved by controlling both the deposition site and quantity. Following the spatially confined alloying treatment, the prepared PtSn alloy catalyst within mesopores demonstrates a small size and homogeneous distribution (2.10 ± 0.53 nm). The membrane electrode assembly with mesoporous carbon-supported PtSn alloy catalyst achieves a high initial mass activity of 0.85 A mg Pt - 1 ${\mathrm{mg}}_{\mathrm{Pt}}^{-1}$ at 0.9 V, which is attributed to the smallest local oxygen transport resistance (3.68 S m-1) ever reported. The mass activity of the catalyst only decreases by 11% after 30000 cycles of accelerated durability test, representing superior full-cell durability among the reported Pt-based alloy catalysts. The enhanced activity and durability are attributed to the decreased adsorption energy of oxygen intermediates on Pt surface and the strong electronic interaction between Pt and Sn inhibiting Pt dissolution.

RESUMEN

Developing efficient bifunctional oxygen electrocatalysts is crucial for enhancing the performance of rechargeable Zn-air batteries (ZABs). In this study, cobalt/cobalt oxides embedded in N-doped carbon nanofibers (Co/CoOx/NCNFs) were synthesized through a combination of electrospinning and annealing processes. The resulting Co/CoOx/NCNFs catalysts feature abundant CoNx and CoOx active species, leveraging the large specific surface area of nanofibers to facilitate oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The optimized Co/CoOx/NCNFs-0.1 achieved a half-wave potential (vs. RHE) of 0.82 V and required only 429 mV to reach 10 mA cm⁻² in a typical three-electrode system with 0.1 M KOH using an electrochemical workstation equipped with a pine instruments rotator, outperforming the Pt/C+RuO2. The assembled ZABs exhibited high specific capacity (771 mAh gZn-1), substantial power density (981.6 mWh gZn-1), and long-term stability (>325 h). In situ Raman spectroscopy confirmed that the electrocatalytic processes involve the redox activity of Co (II and III) species derived from abundant CoNx and CoOx, elaborating the origin of the catalysts' exceptional oxygen electrocatalysis performance. This work not only presents a straightforward and effective approach for producing bifunctional oxygen electrocatalysts in ZABs but also sheds light on the catalytic mechanisms underlying ORR and OER for CoNx/CoOx-based oxygen electrocatalysts.

RESUMEN

Nonprecious metal catalysts, particularly M-N-C catalysts, are widely recognized as promising contenders for the oxygen reduction reaction (ORR). However, a notable performance gap persists between M-N-C catalysts and Pt-based catalysts under acidic conditions. In this study, hybrid catalysts comprising single Co atoms and ultralow concentrations of Pt3Co intermetallic nanoparticles (NPs) are introduced to enhance ORR performance. Under acidic conditions, these hybrid catalysts demonstrate ORR efficiency with a half-wave potential of 0.895 V, negligible decay even after 80 000 cycles, and a high maximum power density of 1.34 W cm-2 in fuel cells. This performance surpasses those of Co-N-C and Pt/Co-N-C catalysts. Both experimental findings and theoretical computations suggest that the heightened ORR activity stems from an increase in the spin density of Co sites induced by noble metal NPs, facilitating the activation of O-O bonds via side-on overlapping and enabling a transition in the reaction pathway from associative to dissociative processes. This research offers a promising avenue for the systematic design of M-N-C cathodes with an enhanced performance for acidic fuel cells.

RESUMEN

Transition metal-based nanoparticles (NPs) are emerging as potential alternatives to platinum for catalyzing the oxygen reduction reaction (ORR) in zinc-air batteries (ZAB). However, the simultaneous coexistence of single-atom moieties in the preparation of NPs is inevitable, and the structural complexity of catalysts poses a great challenge to identifying the true active site. Herein, by employing in situ and ex situ XAS analysis, we demonstrate the coexistence of single-atom moieties and iron phosphide NPs in the N, P co-doped porous carbon (in short, Fe-N4-Fe2P NPs/NPC), and identify that ORR predominantly proceeds via the atomic-dispersed Fe-N4 sites, while the presence of Fe2P NPs exerts an inhibitory effect by decreasing the site utilization and impeding mass transfer of reactants. The single-atom catalyst Fe-N4/NPC displays a half-wave potential of 0.873 V, surpassing both Fe-N4-Fe2P NPs/NPC (0.858 V) and commercial Pt/C (0.842 V) in alkaline condition. In addition, the ZAB based on Fe-N4/NPC achieves a peak power density of 140.3 mW cm-2, outperforming that of Pt/C-based ZAB (91.8 mW cm-2) and exhibits excellent long-term stability. This study provides insight into the identification of true active sites of supported ORR catalysts and offers an approach for developing highly efficient, nonprecious metal-based catalysts for high-energy-density metal-air batteries.

RESUMEN

The effect of NO2, an air pollutant, on the durability of polymer electrolyte membrane fuel cells (PEMFCs) and the affected electrochemical processes in the PEMFC following the contamination were investigated. In-situElectrochemical Impedance Spectroscopy (EIS) measurements were conducted on PEMFCs under different operating conditions of temperature and relative humidity (RH). NO2 was introduced to the cathode inlet flow. Analyses of the EIS measurements were performed using a genetic algorithm called ISGP (Impedance Spectroscopy by Genetic Programming) to obtain the distribution function of relaxation times (DFRT, a.k.a. DRT) models. Utilizing ISGP enabled us to differentiate the various phenomena in PEMFC and study how they are affected by NO2 contamination. Moreover, the experiments demonstrate the effectiveness of the mitigation method to flush the PEMFC and regenerate its performance after being contaminated, particularly at low operating temperatures. Energy-dispersive X-ray spectroscopy (EDS) technique is performed on the contaminated PEMFC to detect the presence of any nitrogen components in the FC's gas diffusion layer and the catalyst layer post the mitigation step. Cyclic Voltammetry is also performed on the contaminated cell to determine the effect of the contamination on the electrochemically active surface area of the cathode by evaluating the double-layer capacitance.