Electrocatalysts For Oxygen Reduction Reaction Research Articles

Hydrophobic-aerophilic composite catalysts enable the fast-charging Zn-air battery to operate 1200 h at 50 mA cm−2

High-efficient bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are central to Zn-air batteries (ZABs). However, the bifunctional activity of catalysts is still unsatisfactory, which restricts the fast-charge performance of ZABs. In this work, we constructed a hydrophobic-aerophilic bifunctional catalyst, where CoFe nanoparticles (NPs) and single atoms (SAs) are separately loaded on zeolite imidazolate fame (ZIF)-derived carbon and hollow carbon tubes respectively (CoFe NP@SA). Thereinto, CoFe SAs are known to be highly active to ORR reaction. Moreover, the in-situ Raman illustrates that CoFe NPs are transformed to CoOOH and FeOOH by electrochemical reconstruction, which can boost the OER activity. Furthermore, the hydrophobic-aerophilic surface can repel water molecules to create abundant solid–liquid-gas three-phase reaction interfaces and expose active sites, which consequently promote the diffusion of reactive molecules/ions across the interface and the oxygen adsorption. Thus, the CoFe NP@SA catalyst exhibit an ultralow ORR/OER potential gap of 0.6 V. After assembled as zinc-air battery (ZAB), it demonstrates a low charge potential (2.09 V) under a high current density of 50 mA cm−2 with the 1200-hour durability. This strategy paves the way to realize the high-power-density and fast-charging ZABs.

Development of Dual N, S‐Heteroatom Doped Hollow Carbon Spheres as an Alternative Electrocatalyst for Oxygen Reduction Reaction in Alkaline Medium

AbstractHollow heteroatom‐doped mesoporous carbons were found to be an efficient non‐noble metal catalyst to enhance the oxygen reduction reaction (ORR) in fuel cells. Here, we use dopamine hydrochloride (DHC) and dibenzyl disulfide (DBS) as the nitrogen and sulfur precursors to infiltrate N and S into the HCS in a single‐step process. Dibenzyl disulfide is less explored in literature as a sulfur dopant. Due to its high sulfur content and high boiling point, dibenzyl disulfide acts as an excellent sulfur dopant and can withstand the carbonization process. Among them, NSMHCS‐0.2 obtained by adding 0.2 g of dibenzyl disulfide at 31 h intervals to the polydopamine (PDA) loaded silica leads to the ideal N, S dual hetero‐atom doping in NSMHCS. Notably, it has a high shell thickness (45 nm), high BET surface area (637 m2 g−1), high pyridinic nitrogen (13.54 %), and thiophene sulfur (89.8 %) concentration. Such property tuning paved the way to reach a high positive onset potential (0.86 V vs RHE) and a limiting current density of 3.64 mA cm−2 at 0.4 V vs RHE. Additionally, NSMHCS‐0.2 has shown superior methanol tolerance and strong electrochemical stability when compared to Pt/C 20 %.

Computational Assistance in the Design of Efficient Oxygen Reduction Reaction Electrocatalysts

AbstractRecently, theoretical calculations have played an irreplaceable role in the discovery of electrocatalysts as a relatively time‐efficient, cost‐effective, and predictable method. More importantly, theoretical calculations can help screen out the best active reaction sites and modulate them accordingly, which is beneficial for the development of efficient catalysts. In this concept, we focus on the important role of theoretical calculations in determining catalytic active sites and understanding reaction mechanisms, emphasizing its importance in assisting the design and synthesis of efficient oxygen reduction reaction catalysts. Finally, we provide an outlook on the challenges and future development trend in this field.

Nitrogen- and fluorine-doped bimetallic carbide as active and stable oxygen reduction reaction electrocatalyst

Nitrogen- and fluorine-doped bimetallic carbide composites with graphite matrix (abbreviated as C19Cr7Mo24/NG and C19Cr7Mo24/FG) are synthesized through carbonization at 1300 °C. The C19Cr7Mo24/NG displays an initial half-wave potential (E1/2) of 0.873 V and suffers merely 3 mV decrease in E1/2 within 60,000 CV cycles for oxygen reduction reaction (ORR) in alkaline media. A H2/O2 fuel cell testing system using the C19Cr7Mo24/NG as cathode maintains 95.9% of the initial peak power density (1.08 W cm−2) within 60,000 cycles. The C19Cr7Mo24/FG shows higher ORR activity than the C19Cr7Mo24/NG. The positive and negative charge centers caused by the N or F dopants are the critical reasons to their high activities. While F and bimetallic carbide more favor electron transfer respectively than the N and monometallic carbide. Their excellent stabilities originate from interactions among atoms due to electron transfer and the intrinsic chemical inertness of graphite and bimetallic carbides.

Preparation of Co[sbnd]N co-doped carbon nanosheets electrocatalyst for efficient oxygen reduction reaction in zinc-air battery

It is very vital that there be a high-activity and serviceable catalyst for the oxygen reduction reaction (ORR) in the Zn-air Battery. Herein, utilizing g-C3N4 as a self-sacrifice template and Cobalt-His framework as the precursor, a simple strategy was developed to synthesize Co/N co-doped carbon nanosheets (CoNC 800) as a metal electrocatalyst for ORR. Due to the Co/N co-doped CoNX site and large specific surface area, the acquired materials show a preeminent ORR catalytic activity with an initial potential (~0.96 V) and half-wave potential (E1/2) of 0.85 V (vs. RHE) in an alkaline medium. Most importantly, the material has superior long-term stability and methanol tolerance than Pt/C. Furthermore, we assembled the Zn-air battery employing catalyst as an air cathode catalyst, demonstrating maximum power densities of 144 mWcm−2, a specific capacity of 821.50 Wh·kg−1, and charge/discharge cycle stability of more than 140 h. The nanosheet structure electrocatalysts derived from the Cobalt-His framework and g-C3N4 provide an innovative and instructive approach to the design of diverse nanomaterials.

Facile Synthesis of Carbon-Based Inks to Develop Metal-Free ORR Electrocatalysts for Electro-Fenton Removal of Amoxicillin.

The electro-Fenton process is based on the generation of hydroxyl radicals (OH•) from hydroxide peroxide (H2O2) generated in situ by an oxygen reduction reaction (ORR). Catalysts based on carbon gels have aroused the interest of researchers as ORR catalysts due to their textural, chemical and even electrical properties. In this work, we synthesized metal-free electrocatalysts based on carbon gels doped with graphene oxide, which were conformed to a working electrode. The catalysts were prepared from organic-gel-based inks using painted (brush) and screen-printed methods free of binders. These new methods of electrode preparation were compared with the conventional pasted method on graphite supports using a binder. All these materials were tested for the electro-Fenton degradation of amoxicillin using a homemade magnetite coated with carbon (Fe3O4/C) as a Fenton catalyst. All catalysts showed very good behavior, but the one prepared by ink painting (brush) was the best one. The degradation of amoxicillin was close to 90% under optimal conditions ([Fe3O4/C] = 100 mg L-1, -0.55 V) with the catalyst prepared using the painted method with a brush, which had 14.59 mA cm-2 as JK and a H2O2 electrogeneration close to 100% at the optimal voltage. These results show that carbon-gel-based electrocatalysts are not only very good at this type of application but can be adhered to graphite free of binders, thus enhancing all their catalytic properties.

Single rhodium atom embedded two dimensional MoSi2N4: A promising electrocatalyst for oxygen reduction reaction

It is essential to develop electrocatalysts that exhibit excellent performance in the oxygen reduction reaction (ORR) for electrochemical energy applications. Recently, MoSi2N4 monolayer has been synthesized and attracted widespread interest. Herein, we constructed a series of structures by embedding transition metal (TM = Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir, Pt and Au) atom into MoSi2N4 with N vacancy (VN-MSN), denoted as TM@VN-MSN, and investigated their ORR activity systematically by first-principles calculations. It is found that TM@VN-MSN systems are stable and there is charge transfer between TM atom and MoSi2N4. After screening, Rh@VN-MSN has the best ORR catalytic activity with an overpotential of 0.35 V, even lower than that of classical Pt (111). Furthermore, an implicit solvation model is used to evaluate the solvent effect. The volcano plots and scaling relations are established based on free energies of intermediates, and verified ΔG*OH can use as a descriptor to explore the ORR activity on TM@VN-MSN. Moreover, d-band center theory and crystal orbital Hamilton populations (COHP) are used to reveal the ORR activity origin. This work not only provide a promising method for designing a new type of MoSi2N4-based ORR catalysts, but also expands its application in the field of electrocatalysis.

Machine-learning-accelerated design of high-performance platinum intermetallic nanoparticle fuel cell catalysts

Carbon supported PtCo intermetallic alloys are known to be one of the most promising candidates as low-platinum oxygen reduction reaction electrocatalysts for proton-exchange-membrane fuel cells. Nevertheless, the intrinsic trade-off between particle size and ordering degree of PtCo makes it challenging to simultaneously achieve a high specific activity and a large active surface area. Here, by machine-learning-accelerated screenings from the immense configuration space, we are able to statistically quantify the impact of chemical ordering on thermodynamic stability. We find that introducing of Cu/Ni into PtCo can provide additional stabilization energy by inducing Co-Cu/Ni disorder, thus facilitating the ordering process and achieveing an improved tradeoff between specific activity and active surface area. Guided by the theoretical prediction, the small sized and highly ordered ternary Pt2CoCu and Pt2CoNi catalysts are experimentally prepared, showing a large electrochemically active surface area of ~90 m2 gPt‒1 and a high specific activity of ~3.5 mA cm‒2.

Disentangling the Activity‐Stability Trade‐Off of Pyrrolic N‐Coordinated Fe─N4 Catalytic Sites for Long‐Life Oxygen Reduction Reaction in Acidic Medium

AbstractFe─N─C materials with Fe─N4 sites are considered as most promising non‐precious metal‐based electrocatalysts for low‐cost proton‐exchange‐membrane fuel cells (PEMFCs). Breaking the trade‐off between activity and stability has been a long‐standing challenge in the field of acidic oxygen reduction reaction (ORR). Herein, a “top‐down” thermally‐driven strategy is developed to achieve highly active pyrrolic N‐coordinated Fe sites in a high spin state with Fe atomic cluster (Fen@Fe─Npyrr─C) and discover that the neighboring Fen cluster can synergistically stabilize such vulnerable Fe─N4 sites by inhibiting their protonation. Consequently, the Fen@Fe─Npyrr─C catalysts exhibit much enhanced ORR activity and stability, endowing PEMFCs with a high power density of 804.6 mW cm−2 (testing conditions: 80 °C, 100% RH, 2.0 bar) and over 100 h durability (at 0.5 V). These findings open up opportunities for the exploration of durable Fe─N─C ORR electrocatalysts for non‐precious metal‐based PEMFCs and other applications.

Metal-organic-framework-derived Fe, Co, N-tri-dopped porous carbon as oxygen electrocatalysts for Zn-air batteries

To commercialize the rechargeable zinc-air (Zn-air) battery, it is desirable but challenging to design highly active, low-cost, stable, and earth-rich bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) to replace rare, expensive, and unstable noble-metal electrocatalysts. Herein, two MOFs are combined under electrostatic interaction and pressure by the way of Ball milling. Then, after post-processing including calcination, acid pickling, and N doping, the bimetal (Fe and Co) and N triple-doped porous carbon electrocatalyst (MIL/ZIF-4-700 °C-NH3) is prepared. Noteworthily, the MIL/ZIF-4-700 °C-NH3 has bimetallic active sites, high contents of pyridine N and graphite N, large surface area, mesoporous structure, and conductive carbon skeletons, which decide the excellent ORR performance. For ORR, the half-wave potential (E1/2 = 0.902 V vs. RHE) of MIL/ZIF-4-700 °C-NH3 is 27 mV higher than that of 20 wt% Pt/C (E1/2 = 0.875 vs. RHE). And the catalyst has also excellent methanol tolerance and stability. The Zn-air battery with MIL/ZIF-4-700 °C-NH3 as cathode catalyst has higher peak power density (176.5 mW cm−2) than that with 20 wt% Pt/C (141.8 mW cm−2) and 20 wt% Pt/C + RuO2 (94.4 mW cm−2) as cathode catalyst. Meanwhile, the Zn-air battery with MIL/ZIF-4-700 °C-NH3 as cathode catalyst exhibits perfect charge-discharge stability (longer than 540 h).

Laser-optimized Pt-Y alloy nanoparticles embedded in Pt-Y oxide matrix for high stability and ORR electrocatalytic activity

The development of active yet stable catalysts for oxygen reduction reaction (ORR) is still a major issue for the extensive permeation of fuel cells into everyday technology. While nanostructured Pt catalysts are to date the best available systems in terms of activity, the same is not true for stability, particularly under operating conditions. In this work, PtXY alloy nanoparticles are proposed as active and durable electrocatalysts for ORR. PtXY nanoalloys are synthesized and further optimized by laser ablation in liquid followed by laser fragmentation in liquid. The novel integrated laser-assisted methodology succeeded in producing PtxY nanoparticles with the ideal size (<10 nm) of commercial Pt catalysts, yet resulting remarkably more active with E1/2 = 0.943 V vs. RHE, specific activity = 1095 μA cm−2 and mass activity > 1000 Ag−1. At the same time, the nanoalloys are embedded in a fine Pt oxide matrix, which allows a greater stability of the catalyst than the commercial Pt reference, as directly verified on a gas diffusion electrode.

Sn Bulk Phase Doping and Surface Modification on Ti4 O7 for Oxygen Reduction to Hydrogen Peroxide.

Developing stable and highly selective two-electron oxygen reduction reaction (2e- ORR) electrocatalysts for producing hydrogen peroxide (H2 O2 ) is considered a major challenge to replace the anthraquinone process and achieve a sustainable green economy. Here, we doped Sn into Ti4 O7 (D-Sn-Ti4 O7 ) by simple polymerization post-calcination method as a high-efficiency 2e- ORR electrocatalyst. In addition, we also applied plain calcination after the grinding method to load Sn on Ti4 O7 (L-Sn-Ti4 O7 ) as a comparison. However, the performance of L-Sn-Ti4 O7 is far inferior to that of the D-Sn-Ti4 O7 . D-Sn-Ti4 O7 exhibits a starting potential of 0.769 V (versus the reversible hydrogen electrode, RHE) and a high H2 O2 selectivity of 95.7 %. Excitingly, the catalyst can maintain a stable current density of 2.43 mA ⋅ cm-2 for 3600 s in our self-made H-type cell, and the cumulative H2 O2 production reaches 359.2 mg ⋅ L-1 within 50,000 s at 0.3 V. The performance of D-Sn-Ti4 O7 is better than that of the non-noble metal 2e- ORR catalysts reported so far. The doping of Sn not only improves the conductivity but also leads to the lattice distortion of Ti4 O7 , further forming more oxygen vacancies and Ti3+ , which greatly improves its 2e- ORR performance compared with the original Ti4 O7 . In contrast, since the Sn on the surface of L-Sn-Ti4 O7 displays a synergistic effect with Tin+ (3≤n≤4) of Ti4 O7 , the active center Tin+ dissociates the O=O bond, making it more inclined to 4e- ORR.

Oxygen reduction mediated by tetrapyridylalkylamine Cu(II) complexes with diimines

Oxygen reduction reaction (ORR) is important in artificial energy conversion systems such as fuel cells. However, it is kinetically sluggish. It is thereby highly desirable to develop ORR catalysts to improve the efficiency of energy conversion. In this work, three copper(II) complexes based on the hexadentate tetrapyridylalkylamine N,N,N’,N’-tetrakis(2-pyridyl-methyl)-1,4-butanediamine (tpbn), namely [Cu2(tpbn)(CH3OH)4(ClO4)2](ClO4)2 (Cu-tpbn), [Cu2(tpbn)(bpy)2](ClO4)4.2CH3COCH3 (Cu-tpbn-bpy, bpy = 2,2′-bipyridine), and [Cu2(tpbn)(Me2bpy)2](ClO4)4.3CH3CN (Cu-tpbn-Me2bpy, Me2bpy = 4,4′-dimethyl-2,2′-bipyridine), were prepared and their catalytic properties for ORR studied. All three complexes were homogeneous electrocatalysts for ORR in neutral phosphate buffer solutions. The ORR mediated by Cu-tpbn-Me2bpy had the most positive onset potential of 0.461 V vs RHE. In the applied potential window of -0.19 – 0.50 V vs RHE, Cu-tpbn boosted the stepwise four-electron ORR to mainly produce H2O, whereas Cu-tpbn-bpy and Cu-tpbn-Me2bpy mediated the ORR to mainly generate H2O2. The rate constants for the ORR to H2O promoted by Cu-tpbn, Cu-tpbn-bpy and Cu-tpbn-Me2bpy were 1.2 × 103 s−1, 3.2 × 10 s−1 and 7.8 × 10 s−1, respectively. The foot-of-the-wave analysis showed that the turnover frequencies for the reduction of O2 to H2O2 mediated by Cu-tpbn, Cu-tpbn-bpy and Cu-tpbn-Me2bpy were 1.5 × 104 s−1, 7.5 × 10 s−1 and 2.7 × 102 s−1, respectively. Meanwhile, complexes Cu-tpbn-bpy and Cu-tpbn-Me2bpy were more stable than Cu-tpbn. This work unveiled that the catalytic activity and the product selectivity of the ORR were greatly associated with the denticity, the steric effect and the electronic property of the organic ligands.

Reticular synthesis of two-dimensional ionic covalent organic networks as metal-free bifunctional electrocatalysts for oxygen reduction and evolution reactions.

Bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are the heart of metal-air batteries, fuel cells, and other energy storage systems. Here, we report a series of a novel class of redox-active viologen-based ionic covalent organic networks (vCONs) which are directly used as metal-free bifunctional electrocatalysts towards ORR and OER applications. These vCONs (named vGC, vGAC, vMEL and vBPDP) were synthesized by the well-known Zincke reaction. The installation of redox-active viologen moieties among the extended covalent organic architectures played a crucial role for exceptional acid/base stability, as well as bifunctional ORR and OER activities, confirmed by the cyclic voltammetry (CV) curves. Among all of them, vBPDP showed high ORR efficiency with a half-wave potential of 0.72 V against a reversible hydrogen electrode (RHE) in 1 M KOH electrolyte. In contrast, vMEL demonstrated high OER activity with an overpotential of 320 mV at a current density of 10 mAcm-2 and a Tafel slope of 109.4 mV dec-1 in 1 M KOH electrolyte solution. This work is exceptional and unique in terms of directly used pristine ionic covalent organic networks that are used as bifunctional (ORR and OER) electrocatalysts without adding any metals or conductive materials.

Component-controlled synthesis of PdxSny nanocrystals on carbon nanotubes as advanced electrocatalysts for oxygen reduction reaction.

Pd-based bimetallic or multimetallic nanocrystals are considered to be potential electrocatalysts for cathodic oxygen reduction reaction (ORR) in fuel cells. Although much advance has been made, the synthesis of component-controlled Pd-Sn alloy nanocrystals or corresponding nanohybrids is still challenging, and the electrocatalytic ORR properties are not fully explored. Herein, component-controlled synthesis of PdxSny nanocrystals (including Pd3Sn, Pd2Sn, Pd3Sn2, and PdSn) has been realized, which are in situ grown or deposited on pre-treated multi-walled carbon nanotubes (CNTs) to form well-coupled nanohybrids (NHs) by a facile one-pot non-hydrolytic system thermolysis method. In alkaline media, all the resultant PdxSny/CNTs NHs are effective at catalyzing ORR. Among them, the Pd3Sn/CNTs NHs exhibit the best catalytic activity with the half-wave potential of 0.85 V (vs. RHE), good cyclic stability, and excellent methanol-tolerant capability due to the suited Pd-Sn alloy component and its strong interaction or efficient electronic coupling with CNTs. This work is conducive to the advancement of Pd-based nanoalloy catalysts by combining component engineering and a hybridization strategy and promoting their application in clean energy devices.

Carbon dot hybrid porous carbon nanofibers as efficient electrocatalysts for the oxygen reduction reaction

C-dots hybrid porous carbon nanofibers (PCNFs) was developed for oxygen reduction reaction. C-dots were used as efficient building blocks for incorporating heteroatoms and defect sites to modify the electronic structure of the PCNFs.

Agri-waste derived electroactive carbon-iron oxide nanocomposite for oxygen reduction reaction: an experimental and theoretical study.

Herein, we have utilized agri-waste and amalgamating low Fe3+, to develop an economic iron oxide-carbon hybrid-based electrocatalyst for oxygen reduction reaction (ORR) with water as a main product following close to 4e- transfer process. The electrocatalytic activity is justified by electrochemical active surface area, synergetic effect, and density functional theory calculations.

Recent advances in trifunctional electrocatalysts for Zn–air batteries and water splitting

The recent advances of trifunctional electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and their applications in Zn–air battery and water splitting, are comprehensively reviewed.

Non-precious metal on zirconium oxide/nitrogen-doped graphene nanocomposite (M/ZrO2-NG) as electrocatalyst for oxygen reduction reaction

Nanocomposite electrocatalysts (M/ZrO2-NG; M: Fe, Co, Fe-Co) consisting of transition metals deposited on zirconium oxide/N-doped graphene were synthesized in the present study. These electrocatalysts were found to be efficient for the oxygen reduction reaction (ORR). A one-step low-temperature solvothermal method was utilized to synthesize nitrogen-doped graphene (NG), which displayed a certain level of alkaline media ORR activity. To enhance both the activity and stability of ORR, ZrO2 was hybridized with NG. Next, a hydrothermal synthesis method was employed to deposit iron and cobalt nanoparticles on ZrO2-NG. The as-prepared electrocatalysts were characterized using various physicochemical, morphological, and electrochemical analyses. FESEM, EDS mapping, HRTEM, XPS, XRD, and FTIR analyses were used to characterize the synthesized NG, ZrO2-NG, and M/ZrO2-NG electrocatalysts. The characterization results indicated that transition metal nanoparticles were homogeneously dispersed on the ZrO2-NG nanocomposite. The electrochemical analysis revealed that the Fe-Co/ZrO2-NG electrocatalyst had the optimal performance with Eonset and E1/2 of 0.872 ± 0.010 and 0.782 ± 0.006 VRHE, respectively, which was comparable to the commercial Pt/C (Eonset = 0.942 ± 0.013 and E1/2 = 0.852 ± 0.009 VRHE). Additionally, chronoamperometric results indicated that the Fe-Co/ZrO2-NG electrocatalyst exhibited better stability (92 % maintenance of its initial current density) than the commercial Pt/C. The high activity and good stability of the optimized nanocomposite electrocatalyst were attributed to the synergistic effect between the zirconium oxide nanoparticles and nitrogen-doped graphene, in addition to the presence of Fe and Co nanoparticles.

ZIF-67-derived Se-doped CoSe2 grown on carbon nanofibers as oxygen electrocatalysts for rechargeable Zn–air batteries

Se-doping can reduce the charge transfer resistance and enhance the OER kinetics. CNFs significantly improved the electrical conductivity of the materials. The ZIF-67-derived carbon skeleton provides an electron transport channel.