Oxygen Reduction Electrocatalysts Research Articles

Manipulation of d-Orbital Electron Configurations in Nonplanar Fe-Based Electrocatalysts for Efficient Oxygen Reduction.

Manipulation of the spin state holds great promise to improve the electrochemical activity of transition metal-based catalysts. However, the underlying relationship between the nonplanar metal coordination environment and spin states remains to be explored. Herein, we report the precise regulation of nonplanar Fe atomic d-orbital energy level into an irregular tetrahedral crystal field configuration by introducing P atoms. With the increase of P coordination number, the spin magnetic moment decreases linearly from 3.8 μB to 0.2 μB, and the high spin content decreases linearly from 31% to 5%. Significantly, a volcanic curve between the spin states of Fe-based catalysts (Fe-NxPy) and oxygen reduction reaction (ORR) activity has been unequivocally established based on the thermodynamic results. Thus, the Fe-N3P1 catalyst with a 19% medium spin state experimentally exhibits the optimal reaction activity with a high half-wave potential of 0.92 V. These findings indicate that regulating electron spin moments through coordination engineering is a promising catalyst design strategy, providing important insights into spin catalysis.

Tuning d-band center of Pt via Pt-Pt5La heterostructure interface as efficient and stable electrocatalyst for oxygen reduction and methanol oxidation reactions in DMFCs

Developing Pt-based electrocatalysts with superior activity and durability is essential for direct methanol fuel cells (DMFCs), and regulating the interfacial electronic interaction for Pt-based composites can significantly modulate the electrocatalytic performances. Herein, the Pt-Pt5La/C heterostructure catalyst was developed to enhance the catalytic property towards oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). Experimental analyses and theoretical calculations demonstrated the electron redistribution at the interface and reduction of the d-band center of Pt for this unique Pt-Pt5La/C heterostructure. As the results, Pt-Pt5La/C exhibited 5.0- and 6.4-times higher mass activity and specific activity towards alkaline ORR compared to Pt/C, and the excellent electrocatalytic MOR performance due to the interfacial interaction. These superior electrocatalytic property promoted Pt-Pt5La/C as the bifunctional catalyst for DMFC application with outstanding power density and durability. Consequently, this work proposed a novel interfacial regulation strategy for designing Pt-rare earth (RE) alloy heterostructures and their reliable operation of DMFCs.

Highly Porous Nitrogen and Phosphorus Dual-Doped Carbon with Increased Phosphorus Content As an Efficient Oxygen Reduction Electrocatalyst

Highly porous nitrogen and phosphorus dual-doped carbon (NPC) was synthesized using acetylene black as a carbon source in two steps: (1) solid–gas mechanochemical treatment to prepare nitrogen-doped carbon (NC), (2) heat treatment to dope the NC with phosphorus. X-ray photoelectron spectroscopy and N2 gas adsorption analysis revealed that the solid–gas mechanochemical treatment using a ball mill incorporated nitrogen atoms into the carbon network and increased the pore volume and surface area. Furthermore, the resulting NC exhibited enhanced reactivity with ammonium dihydrogen phosphate, which was used as a phosphorus source, upon heat treatment. The phosphorus content in NPC synthesized by two-step mechanochemical and heat treatments reached 1.91 at%, a 14-fold increase compared to that of phosphorus-doped carbon synthesized by heat treatment. The NPC exhibited higher electrocatalytic activity for the oxygen reduction reaction than NC, suggesting that the additional phosphorus doping into NC can improve its electrocatalytic performance.

Benchmarking Metal Oxide Electrocatalysts for Oxygen Reduction

Benchmarking Metal Oxide Electrocatalysts for Oxygen Reduction

Spin Manipulation of Heterogeneous Molecular Electrocatalysts by an Integrated Magnetic Field for Efficient Oxygen Redox Reactions.

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.

Machine learning-assisted dual-atom sites design with interpretable descriptors unifying electrocatalytic reactions

Low-cost, efficient catalyst high-throughput screening is crucial for future renewable energy technology. Interpretable machine learning is a powerful method for accelerating catalyst design by extracting physical meaning but faces huge challenges. This paper describes an interpretable descriptor model to unify activity and selectivity prediction for multiple electrocatalytic reactions (i.e., O2/CO2/N2 reduction and O2 evolution reactions), utilizing only easily accessible intrinsic properties. This descriptor, named ARSC, successfully decouples the atomic property (A), reactant (R), synergistic (S), and coordination effects (C) on the d-band shape of dual-atom sites, which is built upon our developed physically meaningful feature engineering and feature selection/sparsification (PFESS) method. Driven by this descriptor, we can rapidly locate optimal catalysts for various products instead of over 50,000 density functional theory calculations. The model’s universality has been validated by abundant reported works and subsequent experiments, where Co-Co/Ir-Qv3 are identified as optimal bifunctional oxygen reduction and evolution electrocatalysts. This work opens the avenue for intelligent catalyst design in high-dimensional systems linked with physical insights.

In situ green architecture of the 3D FeZn-N-C based electrocatalyst for efficient oxygen reduction.

We prepared a 3D FeZn-N-C based catalyst by green in situ growth of 1D Fe-N-C carbon nanotubes by introducing ferrocyanide ions on the surface of 2D exfoliated MOF-5. The 1D/2D FeZn-N-C based electrocatalyst is conducive to O2 diffusion and ionic/electron transfer, exhibiting an excellent ORR catalytic performance and a peak power density of 294 mW cm-2 for Zn-air batteries.

On the role of Zn and Fe doping in nitrogen-carbon electrocatalysts for oxygen reduction

On the role of Zn and Fe doping in nitrogen-carbon electrocatalysts for oxygen reduction

Copper nanoparticles anchored on nitrogen-doped carbon nanofibers derived from MOFs and bacterial cellulose: Advanced electrocatalysts for oxygen reduction in microbial fuel cells

The development of efficient and inexpensive cathode catalysts contributes to energy conservation. Herein, nitrogen-doped carbon nanofiber (CNF) composites (Cu@N-CNFs) loaded with copper nanoparticles were successfully synthesized as cathode electrocatalysts for microbial fuel cells (MFCs), utilizing metal-organic frameworks (MOFs) and bacterial cellulose (BC) as precursors. The characterization results show that Cu@N-CNFs has a large specific surface area and contains catalytic active substances such as pyridine nitrogen and graphite nitrogen, along with that the graphitization degree of carbon skeleton structure is high. Therefore, Cu@N-CNFs has outstanding catalytic performance in alkaline and neutral environments, with half-wave potentials of 0.83 V and 0.78 V, as well as limiting current densities of −5.70 mA cm−2 and −5.73 mA cm−2, respectively. Moreover, these performances are comparable to those of Pt/C. The composite material is coated on the surface of the carbon cloth and processed into MFC cathode, which has a good improvement in its power production performance.

LaCo0.2Fe0.8O3 perovskites doped with natural Ca2+ as bifunctional electrocatalysts for oxygen evolution and reduction reactions.

Perovskite oxides are promising electrocatalysts for various energy applications due to their exceptional catalytic activity, flexible architecture, and low cost. In this study, LCFO was doped with different ratios of Ca2+ from eggshells, resulting in dual-purpose electrocatalysts for oxygen reduction and evolution processes. The nanoparticles were characterized using various techniques, including Brunauer-Emmett-Teller analysis and XRD. Results clarified the relative surface area and roughness, increasing with Ca2+ doping. LCFO also demonstrated highly magnetic properties, improved charge transfer, catalytic activity, and long-term durability. The results demonstrated the perovskite's cost-effectiveness as a bifunctional electrocatalyst, and the role of Ca2+ in enhancing its properties. La0.6Ca0.4Co0.2Fe0.8O3(LCCFO-0.4) showed higher magnetic properties (M s = 13.36 emu g-1 and M r = 2.54 emu g-1). The LCFO sample showed a current density of 5.13 mA cm-2 and 3 mA cm-2 for OER and ORR respectively, at E onset 1.7 V and 0.57 V (vs. RHE). The LCFO electrochemical active surface area is 0.033 cm2.

Metallated graphynes as a bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions: A DFT study

Metallated graphynes as a bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions: A DFT study

Constructing Dual-Phase Co9S8-CoMo2S4 Heterostructure as an Efficient Trifunctional Electrocatalyst for Oxygen Reduction, Oxygen Evolution and Hydrogen Evolution Reactions.

Designing robust, efficient and inexpensive trifunctional electrocatalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is significant for rechargeable zinc-air batteries and water-splitting devices. To this end, constructing heterogenous structures based on transition metals stands out as an effective strategy. Herein, a dual-phase Co9S8-CoMo2S4 heterostructure grown on porous N, S-codoped carbon substrate (Co9S8-CoMo2S4/NSC) via a one-pot synthesis is investigated as the trifunctional ORR/OER/HER electrocatalyst. The optimized Co9S8-CoMo2S4/NSC2 exhibits that ORR has a half-wave potential of 0.86 V (vs. RHE) and the overpotentials at 10 mA cm-2 for OER and HER are 280 and 89 mV, respectively, superior to most transition-metal based trifunctional electrocatalysts reported to date. The Co9S8-CoMo2S4/NSC2-based zinc-air battery (ZAB) has a high open-circuit voltage (1.41 V), large capacity (804 mA h g-1) and highly stable cyclability (97 h at 10 mA cm-2). In addition, the prepared Co9S8-CoMo2S4/NSC2-based ZAB in series can self-drive the corresponding water electrolyzer. The dual-phase Co9S8-CoMo2S4 heterostructure provides not only multi-type active sites to drive the ORR, OER and HER, but also high-speed charge transfer channels between two phases to improve the synergistic effect and reaction kinetics.

Preparation of ultrathin sputtered gold films on palladium as efficient oxygen reduction electro-catalysts

Herein, we present the preparation of ultrathin gold (Au) films on different M (M = Pd, Pt, Rh, Ir, and Ru) electrodes (Au/M) using magnetron sputtering deposition for oxygen reduction reaction (ORR). The ORR electro-catalytic activities of prepared Au/M catalysts increase as follows: Au/Ru < Au/Ir < Au/Rh < Au/Pt < Au/Pd. Accordingly, the oxygen reduction catalytic behaviors of the Au-modified palladium (Au/Pd) thin films with various Au thicknesses (0.16, 0.24, 0.5, and 1 nm) are investigated in acidic environments. It is found that Au modifications can promote oxygen reduction performances due to the development of more catalytic active sites on the Pd catalyst through the existence of Au atoms. Noticeably, Au/Pd samples exhibit a connection in oxygen reduction ability as a function of Au thickness, with the ultrathin 0.16 nm Au/Pd being the most active ORR catalyst. Significantly, the 0.16 nm Au/Pd material demonstrates superior stability after 1000 potential cycles compared with the 0.16 nm Pt/Pd owing to the influence of Au coating and structurally stable surfaces. Therefore, surface modification with the deposition of Au films on Pd represents a favorable technique to boost both the ORR capability and stability of the electro-catalysts.

Crystalline 1D Linear Conjugated Polymers with a Quinoidal Unit As Metal‐Free Electrocatalysts for Oxygen Reduction

AbstractCrystalline and soluble 1D linear conjugated polymers (LCPs) have garnered considerable interest as cost‐effective and efficient metal‐free electrocatalysts for the oxygen reduction reaction (ORR) due to their high exposure of catalytic sites and ease of processing. However, difficulties remain in achieving excellent ORR performance for 1D LCPs by conventional molecular design. Herein, it is demonstrated the utilization of quinoidal units as a promising strategy to develop 1D LCPs for ORR. The incorporation of quinoidal unit not only results in polymers with strong inter‐ and intra‐molecular interactions and low‐lying LUMO (lowest unoccupied molecular orbital) energy levels, but also provides polymers with good crystallinity and commendable charge carrier mobilities. The electronic properties of these polymers are fine‐tuned through the introduction of additional heteroatoms and/or substituents in the monomers and comonomers to understand and optimize their ORR catalytic activity. Evaluation of their catalytic performances reveals a remarkable half‐wave potential and limiting current density of up to 0.74 V (vs reversible hydrogen electrod) and 7.50 mA cm−2, respectively. Notably, these performances are achieved without the addition of carbon nanomaterials as support. This study offers a new insight into the design of highly efficient metal‐free organic electrocatalysts.

Accelerating the Discovery of Oxygen Reduction Electrocatalysts: High‐Throughput Screening of Element Combinations in Pt‐Based High‐Entropy Alloys

AbstractThe vast number of element combinations and the explosive growth of composition space pose significant challenges to the development of high‐entropy alloys (HEAs). Here, we propose a procedural research method aimed at accelerating the discovery of efficient electrocatalysts for oxygen reduction reaction (ORR) based on Pt‐based quinary HEAs. The method begins with an element library provided by a large language model (LLM), combined with microscale precursor printing and pulse high‐temperature synthesis techniques to prepare multi‐element combination HEA array in one step. Through high‐throughput measurement using scanning electrochemical cell microscopy (SECCM), precise identification of highly active HEA element combinations and exploration of composition space for a specific combination are achieved. Advantageous element combinations are further validated in practical electrocatalytic evaluations. The contributions of individual element sites and the synergistic effects among elements of such HEAs in enhancing reaction activity are elucidated via density functional theory (DFT) calculations. This method integrates high‐throughput experiments, practical catalyst validation, and DFT calculations, providing a new pathway for accelerating the discovery of efficient multi‐element materials in the field of energy catalysis.

Hydrogen Peroxide Spillover on Platinum-Iron Hybrid Electrocatalyst for Stable Oxygen Reduction.

Iron-nitrogen-carbon (Fe-N-C) catalysts, although the most active platinum-free option for the cathodic oxygen reduction reaction (ORR), suffer from poor durability due to the Fe leaching and consequent Fenton effect, limiting their practical application in low-temperature fuel cells. This work demonstrates an integrated catalyst of a platinum-iron (PtFe) alloy planted in an Fe-N-C matrix (PtFe/Fe-N-C) to address this challenge. This novel catalyst exhibits both high-efficiency activity and stability, as evidenced by its impressive half-wave potential (E1/2) of 0.93 V versus reversible hydrogen electrode (vs RHE) and minimal 7 mV decay even after 50,000 potential cycles. Remarkably, it exhibits a very low hydrogen peroxide (H2O2) yield (0.07%) at 0.6 V and maintains this performance with negligible change after 10,000 potential cycles. Fuel cells assembled with this cathode PtFe/Fe-N-C catalyst show exceptional durability, with only 8 mV voltage loss at 0.8 A cm-2 after 30,000 cycles and ignorable current degradation at a voltage of 0.6 V over 85 h. Comprehensive in situ experiments and theoretical calculations reveal that oxygen species spillover from Fe-N-C to PtFe alloy not only inhibits H2O2 production but also eliminates harmful oxygenated radicals. This work paves the way for the design of highly efficient and stable ORR catalysts and has significant implications for the development of next-generation fuel cells.

Installing Quinol Proton/Electron Mediators onto Non-Heme Iron Complexes Enables Them to Electrocatalytically Reduce O2 to H2O at High Rates and Low Overpotentials.

We prepare iron(II) and iron(III) complexes with polydentate ligands that contain quinols, which can act as electron proton transfer mediators. Although the iron(II) complex with N-(2,5-dihydroxybenzyl)-N,N',N'-tris(2-pyridinylmethyl)-1,2-ethanediamine (H2qp1) is inactive as an electrocatalyst, iron complexes with N,N'-bis(2,5-dihydroxybenzyl)-N,N'-bis(2-pyridinylmethyl)-1,2-ethanediamine (H4qp2) and N-(2,5-dihydroxybenzyl)-N,N'-bis(2-pyridinylmethyl)-1,2-ethanediamine (H2qp3) were found to be much more active and more selective for water production than a previously reported cobalt-H2qp1 electrocatalyst while operating at low overpotentials. The catalysts with H2qp3 can enter the catalytic cycle as either Fe(II) or Fe(III) species; entering the cycle through Fe(III) lowers the effective overpotential. On the basis of their TOF0 values, the successful iron-quinol complexes are better electrocatalysts for oxygen reduction than previously reported iron-porphyrin compounds, with the Fe(III)-H2qp3 arguably being the best homogeneous electrocatalyst for this reaction. With iron, the quinol-for-phenol substitution shifts the product selectivity from H2O2 to water with little impact on the overpotential, but unlike cobalt, this substitution also greatly improves the activity, as assessed by TOFmax, by hastening the protonation and oxygen binding steps. The addition of a second quinol further enhances the activity and selectivity for water but modestly increases the effective overpotential.

FeMnO3/CNT as a synergistic bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions in alkaline medium

The development of highly effective and low-cost electrocatalysts for energy conversion and storage devices is triggered by the sluggish kinetics of oxygen reduction and evolution reactions. Perovskite-based oxides are identified as potential ORR and OER electrocatalysts in an alkaline medium. Thus, the present study discusses the synthesis and characterization of FeMnO3/CNT as a bifunctional catalyst with a low potential gap of 0.89 V. The FeMnO3/CNT composite was synthesized by the solution combustion method and characterized using spectroscopic and electron microscopic techniques. The increase in the ID/IG ratio obtained from the Raman spectra of the FeMnO3/CNT composite with respect to bare CNT indicates the functionalization of CNT. The ORR and OER characteristics of the FeMnO3/CNT composite were analyzed with rotating ring disc electrode and rotating disc electrode measurements. The LSV curve of the FeMnO3/CNT composite synthesized with 0.3g of CNT show better ORR and OER activity. The ORR activity measurements of the composite done in 0.1 M KOH electrolyte show a good onset potential of 0.95 V vs. RHE and a half-wave potential of 0.74 V. The HPRR studies show that the ORR reaction mechanism follows a 2e− + 2e− reduction pathway. The OER measurements in an alkaline medium show an onset potential of 1.63 V vs. RHE with a Tafel slope of 115.3 mV dec−1. Also, this work gives an insight into the fundamental understanding of the synergy between the perovskite and CNT, leading to an enhanced ORR and OER catalytic activity. In addition, the material exhibits good stability for ORR and OER stability studies.

Facile Carbothermal Synthesis of Metal Phosphides-Based Multifunctional Electrocatalysts via Polyaniline Doped with Phosphoric Acid

Transition metal phosphides (TMPs) and their composites are promising non-platinum electrocatalysts for hydrogen evolution (HER), oxygen evolution (OER), and oxygen reduction (ORR) reactions. But traditional methods to obtain these electrocatalysts are usually multi-step and include the participation of hazardous phosphorus compounds during phosphidation. Here, the possibility of using a polyaniline doped with phosphoric acid (PANI∙H3PO4)—as a source of C, N and P simultaneously - to obtain composites based on N,P-doped carbon and nano- and/or submicron TMP particles as HER, OER and ORR electrocatalysts is demonstrated. The pyrolysis of PANI∙H3PO4 together with Co, Ni, Mo, or Fe salt allows the formation of such composite electrocatalysts by the carbon thermal reduction route. Regardless of the pH of the electrolyte, the MoP-based electrocatalyst is characterized in HER by the smallest Tafel slope and overpotential of hydrogen evolution and also exhibits high stability during long-term operation. At the same time, other composites are multifunctional electrocatalysts possessing activity not only in HER, but also in OER and ORR. The proposed approach can be a starting point for a simple, universal in choice of d-metal, and environmentally attractive preparation of multifunctional TMP-based electrocatalysts with further improvement of their performance.

Synergistically improving the performance of spinel cathode for efficient oxygen reduction electrocatalyst

Optimizing the performance of ceramic fuel cells requires the creation of effective and inexpensive electrocatalysts for the oxygen reduction process. Here, we detail a plan for converting the inert spinel CoAl2O4 into a highly active and superior material for low-temperature ceramic fuel cells through Fe substitution. It turns out that the iron substitution aids in surface reconstruction, increasing oxidation-reduction reaction (ORR) activity. In addition, the reduction in energy bandgap due to Fe doping enhance the Cathode ORR performance, which may be triggered by the ions' kinetics at the surface and interface. The surface layer and Fe doping considerably aid the oxidation-reduction reaction, which creates more oxygen vacancies at the active oxygen site. The prepared materials exhibit enhanced fuel cell performance of 542 mW/cm2 at a temperature of 520 °C. Remarkably, the prepared cathode exhibits a commendable performance of 200 mW/cm2 at a temperature of 420 °C.Furthermore, the CoFe1Al1O4 cell exhibits a decreased Rp (polarization resistance) value of 0.6423 ohm-cm2 at a temperature of 520 °C, demonstrating rapid ORR kinetics. The distribution relaxation time (DRT) shows that the Cathode oxidation-reduction reaction (ORR) activity increased with Fe doping. We present a promising method for improving the oxidation-reduction reaction efficiency of low-temperature ceramic fuel cells.