Oxygen Reduction Electrocatalysts Research Articles

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.

A self‐powered system to electrochemically generate ammonia driven by palladium single atom electrocatalyst

AbstractThe utilization of single atoms (SAs) as trifunctional electrocatalyst for nitrogen reduction, oxygen reduction, and oxygen evolution reactions (NRR, ORR, and OER) is still a formidable challenge. Herein, we devise one‐pot synthesized palladium SAs stabilized on nitrogen‐doped carbon palladium SA electrocatalyst (Pd‐SA/NC) as efficient trifunctional electrocatalyst for NRR, ORR, and OER. Pd‐SA/NC performs a robust catalytic activity toward NRR with faradaic efficiency of 22.5% at −0.25 V versus reversible hydrogen electrode (RHE), and the relative Pd utilization efficiency is enhanced by 17‐fold than Pd‐NP/NC. In addition, the half‐wave potential reaches 0.876 V versus RHE, amounting to a 58‐time higher mass activity than commercial Pt/C. Moreover, the overpotential at 10 mA cm−2 is as low as 287 mV for Pd‐SA/NC, outperforming the commercial IrO2 by 360 times in turnover frequency at 1.6 V versus RHE. Accordingly, the assembled rechargeable zinc‐air battery (ZAB) achieves a maximum power density of 170 mW cm−2, boosted by 2.3 times than Pt/C–IrO2. Two constructed ZABs efficiently power the NRR‐OER system to electrochemically generate ammonia implying its superior trifunctionality.

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.

Compressively Strained Fe3O4 in Core-Shell Oxygen Reduction Electrocatalyst Boosts Zinc-Air Battery Performance.

Fe3O4 is barely taken into account as an electrocatalyst for oxygen reduction reaction (ORR), an important reaction for metal-air batteries and fuel cells, due to its sluggish catalytic kinetics and poor electron conductivity. Herein, how strain engineering can be employed to regulate the local electronic structure of Fe3O4 for high ORR activity is reported. Compressively strained Fe3O4 shells with 2.0% shortened Fe─O bond are gained on the Fe/Fe4N cores as a result of lattice mismatch at the interface. A downshift of the d-band center occurs for compressed Fe3O4, leading to weakened chemisorption energy of oxygenated intermediates, and lower reaction overpotential. The compressed Fe3O4 exhibits greatly enhanced electrocatalytic ORR activity with a kinetic current density of 27 times higher than that of pristine one at 0.80V (vs reversible hydrogen electrode), as well as potential application in zinc-air batteries. The findings provide a new strategy for tuning electronic structures and improving the catalytic activity of other metal catalysts.

Iron-Cobalt Phosphide Encapsulated in a N-Doped Carbon Framework as a Promising Low-Cost Oxygen Reduction Electrocatalyst for Zinc-Air Batteries.

The oxygen reduction reaction (ORR) plays a vital role in many next-generation electrochemical energy conversion and storage devices, motivating the search for low-cost ORR electrocatalysts possessing high activity and excellent durability. In this work, we demonstrate that iron-cobalt phosphide (FeCoP) nanoparticles encapsulated in a N-doped carbon framework (FeCoP@NC) represent a very promising catalyst for the ORR in alkaline media. The core-shell structured FeCoP@NC catalyst offered outstanding ORR activity with a half-wave potential (E1/2) of 0.86 V vs reversible hydrogen electrode (RHE) and excellent stability in a 0.1 M KOH electrolyte, outperforming commercial Pt/C and many recently reported noble-metal-free ORR electrocatalysts. The superiority of FeCoP@NC as an ORR electrocatalyst relative to Pt/C was further verified in prototype zinc-air batteries (ZABs), with the aqueous and flexible ZABs prepared using FeCoP@NC offering excellent stability, impressive open circuit voltages (1.56 and 1.44 V, respectively), and high maximum power densities (183.5 and 69.7 mW cm-2, respectively). Density functional theory calculations revealed that encapsulating FeCoP nanoparticles in N-doped carbon shells resulted in favorable electron penetration effects, which synergistically regulated the adsorption/desorption of ORR intermediates for optimal ORR performance while also boosting the electronic conductivity. Our findings offer valuable new insights for rational design of transition metal phosphide-based catalysts for the ORR and other electrochemical applications.

Mn-modified nitrogen-doped Pt-based electrocatalyst for efficient oxygen reduction in aluminum-air batteries

Mn-modified nitrogen-doped Pt-based electrocatalyst for efficient oxygen reduction in aluminum-air batteries

Epitaxial growth of highly atomically ordered Pt-Fe nanoparticles from carbon nanotube bundles as durable oxygen reduction electrocatalysts

Intermetallic Pt-based nanoparticles have displayed excellent activity for the oxygen reduction reaction (ORR) in fuel cells. However, it remains a great challenge to synthesize highly atomically ordered Pt-based nanoparticle catalysts because the formation of an atomically ordered structure usually requires high-temperature annealing accompanied by grain sintering. Here we report the direct epitaxial growth of well-aligned, highly atomically ordered Pt3Fe and PtFe nanoparticles (<5 nm) on single-walled carbon nanotube (SWCNT) bundles films. The long-range periodically symmetric van der Waals (vdW) interactions between SWCNT bundles and Pt-Fe nanoparticles play an important role in promoting not only the alignment ordering of inter-nanoparticles but also the atomic ordering of intra-nanoparticles. The ordered Pt3Fe/SWCNT catalyst showed enhanced ORR catalytic performance of 2.3-fold higher mass activity and 3.1-fold higher specific activity than commercial Pt/C. Moreover, the formation of an interlocked interface and strong vdW interaction endow the Pt-Fe/SWCNT catalysts with extreme long-term stability in potential cycling and excellent anti-thermal sintering ability.

Study of the Suitability of Corncob Biochar as Electrocatalyst for Zn–Air Batteries

There has been a recent increasing interest in Zn–air batteries as an alternative to Li-ion batteries. Zn–air batteries possess some significant advantages; however, there are still problems to solve, especially related to the tuning of the properties of the air–cathode which should carry an inexpensive but efficient bifunctional oxygen reduction (ORR) and oxygen evolution (OER) reaction electrocatalyst. Biochar can be an alternative, since it is a material of low cost, it exhibits electric conductivity, and it can be used as support for transition metal ions. Although there is a significant number of publications on biochars, there is a lack of data about biochar from raw biomass rich in hemicellulose, and biochar with a small number of heteroatoms, in order to report the pristine activity of the carbon phase. In this work, activated biochar has been made by using corncobs. The biomass was first dried and minced into small pieces and pyrolyzed. Then, it was mixed with KOH and pyrolyzed for a second time. The final product was characterized by various techniques and its electroactivity as a cathode was determined. Physicochemical characterization revealed that the biochar had a hierarchical pore structure, moderate surface area of 92 m2 g−1, carbon phase with a relatively low sp2/sp3 ratio close to one, and a limited amount of N and S, but a high number of oxygen groups. The graphitization was not complete while the biochar had an ordered structure and contained significant O species. This biochar was used as an electrocatalyst for ORR and OER in Zn–air batteries where it demonstrated a satisfactory performance. More specifically, it reached an open-circuit voltage of about 1.4 V, which was stable over a period of several hours, with a short-circuit current density of 142 mA cm−2 and a maximum power density of 55 mW cm−2. Charge–discharge cycling of the battery was achieved between 1.2 and 2.1 V for a constant current of 10 mA. These data show that corncob biochar demonstrated good performance as an electrocatalyst in Zn–air batteries, despite its low specific surface and low sp2/sp3 ratio, owing to its rich oxygen sites, thus showing that electrocatalysis is a complex phenomenon and can be served by biochars of various origins.

Cathodic Electrosynthesis of H2O2 Using Sustainable Cellulose‐Co‐ZIF Electrocatalyst

AbstractManufacturing the biochar‐derived 2e‐electron oxygen reduction (2e‐ORR) electrocatalyst from sustainable biomass promises a cost‐effective alternative for typical petroleum‐based resources, but still suffers from inferior catalytic activity and low 2e‐ORR selectivity. Here, the study demonstrates a simple and effective strategy for achieving high‐performance sustainable Co‐ZIF‐engineered cellulose electrocatalyst, enabling in situ growth of nanostructured ZIF‐67 particles around the abundant hydrophilic oxygen‐containing micro‐scale cellulose fibers. Through a simple one‐step pyrolysis at 900 °C of the cellulose‐Co‐ZIF substrate, a high‐porosity carbonous the Co‐ZIF‐CC catalyst is obtained that possesses active sites and carbon defects, facilitating 2e‐ORR progress for H2O2 production. By utilizing O2 as reaction gas, it can electrochemically generate H2O2 concentration attaining up to 555.1 mg L−1, outperforming a nearly five‐fold increase compared to that using air, and also showing about maximin thirty times higher compared to exiting biochar‐based 2e‐ORR electrocatalysts from biomass. The proposed cellulose‐Co‐ZIF strategy breakthroughs the next generation of sustainable 2e‐ORR electrocatalysts from renewable bioresources with low‐cost, economic ecology, beyond the wide potential applications for other electrocatalysts.

Integration Construction of Hybrid Electrocatalysts for Oxygen Reduction.

There is notable progress in the development of efficient oxygen reduction electrocatalysts, which are crucial components of fuel cells. However, these superior activities are limited by imbalanced mass transport and cannot be fully reflected in actual fuel cell applications. Herein, the design concepts and development tracks of platinum (Pt)-nanocarbon hybrid catalysts, aiming to enhance the performance of both cathodic electrocatalysts and fuel cells, are presented. This review commences with an introduction to Pt/C catalysts, highlighting the diverse architectures developed to date, with particular emphasis on heteroatom modification and microstructure construction of functionalized nanocarbons based on integrated design concepts. This discussion encompasses the structural evolution, property enhancement, and catalytic mechanisms of Pt/C-based catalysts, including rational preparation recipes, superior activity, strong stability, robust metal-support interactions, adsorption regulation, synergistic pathways, confinement strategies, ionomer optimization, mass transport permission, multidimensional construction, and reactor upgrading. Furthermore, this review explores the low-barrier or barrier-free mass exchange interfaces and channels achieved through the impressive multidimensional construction of Pt-nanocarbon integrated catalysts, with the goal of optimizing fuel cell efficiency. In conclusion, this review outlines the challenges associated with Pt-nanocarbon integrated catalysts and provides perspectives on the future development trends of fuel cells and beyond.

Reconstruction of High Entropy Alloys on a Metal–Organic Framework Approaching Active Oxygen Reduction Electrocatalysts

Reconstruction of High Entropy Alloys on a Metal–Organic Framework Approaching Active Oxygen Reduction Electrocatalysts

Transition Metal-Based Polyoxometalates for Oxygen Electrode Bifunctional Electrocatalysis

Polyoxometalates (POMs) with transition metals (Co, Cu, Fe, Mn, Ni) of Keggin structure and lamellar-stacked multi-layer morphology were synthesized. They were subsequently explored as bifunctional electrocatalysts for oxygen electrodes, i.e., oxygen reduction (ORR) and evolution (OER) reaction, for aqueous rechargeable metal-air batteries in alkaline media. The lowest Tafel slope (85 mV dec−1) value and the highest OER current density of 93.8 mA cm−2 were obtained for the Fe-POM electrocatalyst. Similar OER electrochemical catalytic activity was noticed for the Co-POM electrocatalyst. This behavior was confirmed by electrochemical impedance spectroscopy, where Fe-POM gave the lowest charge transfer resistance of 3.35 Ω, followed by Co-POM with Rct of 15.04 Ω, during the OER. Additionally, Tafel slope values of 85 and 109 mV dec−1 were calculated for Fe-POM and Co-POM, respectively, during the ORR. The ORR at Fe-POM proceeded by mixed two- and four-electron pathways, while ORR at Co-POM proceeded exclusively by the four-electron pathway. Finally, capacitance studies were conducted on the synthesized POMs.

Cobalt–nickel bimetallic hybridized nitrogen-doped hierarchical porous carbon as efficient oxygen reduction electrocatalyst

Cobalt–nickel bimetallic hybridized nitrogen-doped hierarchical porous carbon as efficient oxygen reduction electrocatalyst