Electrocatalyst Research Articles

Repurposing discarded porphyrin waste as electrocatalysts for the oxygen reduction reaction

The oxygen reduction reaction (ORR), presently known as the key bottleneck in the mass-scale implementation of fuel cells (FCs), typically relies on the exploitation of scarce and expensive platinum group metals (PGMs). Meanwhile, as a substitute for PGMs, transition metal-nitrogen carbons (TM-Nx-C) are proving to be reliable electrocatalysts (ECs) in which atomically dispersed TMs coordinated with nitrogen are integrated into the carbon matrix. Such TM-Nx coordination already exists in metal-porphyrins making them suitable precursors for TM-Nx-C. Adler-Longo method is the standard recipe for meso‑tetraphenyl porphyrin realizes ca. 20 % yield whereas the residual polypyrromethenes, structurally resembling open porphyrin rings, are often wasted. Herein, the possibility of upcycling waste polypyrromethenes into efficient TM-Nx-C for ORR is demonstrated. A comprehensive structural and morphological characterization is provided, and the electrocatalytic activity towards ORR in an alkaline environment is discussed using Fe and Mn as TMs. The EC synthesized from pure porphyrin precursor at 600 °C (FeTPP_600) had the best performance recording 0.972 and 0.852 V vs RHE for Eonset and E1/2. Mixing porphyrins with their synthetic waste (ratio of 1:4) and pyrolyzing it at 800 °C (FeTPP/Waste(1:4)_800) still exhibits appreciable kinetics with similar results (0.977 and 0.853 V vs RHE for Eonset and E1/2).

(Invited) Electrocatalysts for the Oxygen Reduction Reaction and the Hydrogen Evolution Reaction Based on “Core-Shell”, “PGM-Free” Carbon Nitride Systems

The key electrochemical processes at the heart of the “hydrogen economy” involve: (i) the recombination of hydrogen and oxygen to form water in fuel cells (FCs); and (ii) the splitting of water to yield hydrogen and oxygen in water electrolyzers (ELs). Depending on the particular device taken under consideration, such processes typically occur either in a highly acidic environment (e.g., in proton-exchange membrane fuel cells, PEMFCs, and in proton-exchange membrane electrolyzers, PEMELs) or in strongly alkaline conditions (e.g., in anion-exchange membrane fuel cells, AEMFCs; and in anion-exchange membrane electrolyzers, AEMELs). In both cases, such processes require suitable electrocatalysts (ECs) to minimize overpotentials and achieve a performance and durability level compatible with applications. State-of-the-art ECs for both FCs and ELs typically suffer from important drawbacks such as: (i) high overpotentials; (ii) a poor durability; and (iii) a high loading of strategic elements, with a particular reference to platinum-group metals (PGMs); correspondingly, significant concerns are raised due to potential supply bottlenecks.In this work, a new family of “PGM-free” ECs is proposed, especially targeted to promote the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER) in either/both the acidic and the alkaline environment. The ECs are obtained by means of a multi-step synthetic process [1]. In the first step a precursor is prepared by coupling a carbon black support with a hybrid inorganic-organic macromolecular system consisting of an organic binder coordinating: (i) a first-row transition metal (e.g., Fe) meant to act as the “catalyst”; and (ii) Sn, playing the role of “co-catalyst”. Subsequently the precursor undergoes a multi-step pyrolysis process followed by suitable chemical treatments meant to remove labile species and reaction byproducts, yielding the final EC. Optionally, the EC may be coupled with an additional aliquot of the hybrid-inorganic precursor. In this case, further pyrolysis/chemical treatment steps are carried out to obtain the final product.The final “PGM-free” ECs proposed herein exhibit a “core-shell” morphology. The carbon black “core” is covered by a carbon nitride “shell” stabilizing the active sites based on the “catalyst” and the “co-catalyst” into C- and N- “coordination nests”. The ECs undergo an extensive physicochemical characterization, meant to determine: (i) the chemical composition, both in the bulk and on the surface (adopting analytical techniques such as ICP-AES, CHNS microanalysis, EDX and NAP-XPS); (ii) the morphology (by means of UHR-SEM); (iii) the porosimetric features (by nitrogen and water physisorption studies); and (iv) the structure (e.g., through wide-angle X-ray diffraction). The kinetics and reaction mechanism of the proposed ECs in the ORR and HER are determined by advanced electroanalytical techniques, with a particular reference to cyclic voltammetry with the thin-film rotating ring-disk electrode (CV-TF-RRDE). The synthetic parameters are finally correlated with the results of the physicochemical and the electrochemical characterization, shedding light on the most promising avenues to guide the preparation of further ECs exhibiting improved performance and durability, suitable for implementation in next-generation FCs and ELs.

Boosting Oxygen Electrocatalysis via Pre-Magnetized Multi Metallic Electrocatalyst

The quest for highly efficient durable and cost-effective electro catalysts for oxygen evolution reaction (OER) remains a pivotal focus in the advancement of renewable energy conversion technologies. Transition metal-based alkaline media electrocatalysts have emerged as promising candidates due to their versatile electronic structures and cost effectiveness. Among these, magneto-electrocatalysts, integrating magnetic properties with electrocatalytic functionalities, represent a novel frontier in OER research. In this study, we introduce a novel approach to enhance OER performance via the utilization of pre-magnetized multi-metallic (Fe-Ni-Co ) doped electrocatalysts, harnessing electron spin polarization. We tailored the electronic structure and magnetic properties of the catalyst, promoting and validating the principle of spin polarization for augmenting OER activity. Through a comprehensive experimental study, we have investigated how the inclusion of magnetic components influences the catalytic activity, stability, and overall efficiency of the electrocatalyst during OER. Experimental methodologies involving material synthesis, characterization techniques (XRD,FE-SEM, VSM study) and electrochemical analysis are employed to assess the structural, magnetic, and electrocatalytic properties of the synthesized pre-magnetised electrocatalyst.We employed the Fe-modified Nickel foam (NF) substrate as a catalyst support. Three distinct electrocatalysts (EC) [NF/Fe-Ni, NF/Fe-Co, and NF/Fe-NiCo] were electrodeposited in two different types: (electrodeposition without magnetic field) and (electrodeposition with applied magnetic field 0.6 T). Observations revealed that for all three electrocatalyst, the electrocatalysts [which were synthesized by applying a magenetic field during eletro deposition and later on OER activity was measured in the absence of magnetic field ] exhibit superior electrocatalytic activity towards OER compared to its counterparts . The highest electrocatalytic activity is provided by NF/Fe-NiCo of 0.5 mA/cm2 ECSA in the absence of a magnetic field and 0.533 mA/ cm2 ECSA in the presence of magnetic field. This is superior to that of the precious metal Ru, which has a specific activity of 0.49 mA/ cm2 ECSA at 1.5V (versus RHE). After analysing the OER performance of the catalyst, we found that the activity of NF/Fe-NiCo improved from 69.15 to 89.55 mA/ cm2 when a magnetic field was applied. Capacitance measurements (15.16% increase) and ECSA measurements (22.1% increase) also corroborated this. The overpotential measurement decreased from 243.03 mV to 239.1 mV at 100 mA/ cm2. As a result, for both sets of catalysts, the magnetic field improved the current density. Comparatively OER performance in absence of magnetic field of the electrocatalyst which was synthesized by electrodeposition with applied magnetic field was better than (for the second catalyst OER activity studied under applied magnetic field. This suggests that rather than applying a magnetic field during long-term electrolysis, one may opt to apply a magnetic field during electrocatalyst production. When we compared the OER performance of these two, we discovered that NF/Fe-NiCo exhibits the greatest activity of all catalysts at 1.5V, with 91.3 mA/ cm2, although the percentage rise is lower than that of the other catalysts. However, compared to the rise in activity, the ECSA data reveals a significant increment of 56%. The data on capacitance and overpotential likewise correspond with the current density trend. With the lowest overpotential of 236.35 mV when measured at 100 mA/cm2, the NF/NiCo catalyst performed the best overall among all the catalysts. Our findings underscore the significance of electron spin polarization in boosting electrocatalytic performance, offering a promising avenue for the design and development of advanced catalysts for sustainable energy applications and in the context of their commercial viability and integration into industrial-scale electrochemical devices.

Tuning Oxygen Evolving Catalytic Activity of a Precious Metal-Free Nickel Boride by a Cost-Effective Method

The production of hydrogen (H2) by electrochemical water splitting [Green Hydrogen (Green H2)], if driven by green electricity, has attracted considerable interest as an alternative sustainable energy carrier, e.g., in fuel cells for electricity or power and heat generation [1]. However, the lack of satisfactory and cheap electrocatalysts (ECs) to drive the vital electrochemical reactions of hydrogen evolution (HER) and oxygen evolution (OER) in water splitting is the biggest challenge for this technology.Currently, the most advanced electrocatalysts for the two half-reactions of water electrolysis (HER and OER) are noble metal-based materials [2]. Despite the excellent catalytic properties of these noble metal catalysts, their high cost, and scarcity make their commercial use both uneconomical and impractical in low temperature water electrolysis (LT-WE) systems at industrial scale for green H2 as a clean energy alternative to cheaper fossil fuels[3]. In addition to addressing this issue by the development of precious-material-based with a low-loading of precious metal elements, the development of desirable and high-efficiency electrocatalysts (ECs) based on earth-abundant metal elements materials is paramount. However, their catalytic activity is often limited by poor electron transfer, low conductivity, low stability, and small surface area of these materials. Thus, it is crucial to develop earth-abundant metal elements-based materials that are more cost-effective to reduce the high cost of active catalysts for water electrolysis. Although several low-cost materials have already been designed, the potential required for the practical application of water splitting is still very high compared to the theoretical potential (1.23 V), which means that much energy is consumed, which theoretically could be reduced. Due to their remarkable advanced charge transfer and durability for water oxidation in alkaline media, electrocatalysts derived from metal borides-based materials have received a lot of attention as new high-performance catalysts for water oxidation.[4] These properties stem from the multi-dimensional covalent bonding of the metalloid with the surrounding metal atoms.We present here an approach to tune the OER of transition metal borides (TMBs) using the cost-effective and less energy-consuming method that is nevertheless a highly efficient material for OER (Fig. 1). We have developed a low-cost, rational and easily scalable method to enhance the catalytic activity of nickel boride (Ni–B), which requires an annealing process to optimize the catalytic activity. However, this method may have limited applicability on a large scale as it requires a highly inert environment and high-temperature treatment of Ni–B catalysts. We also elucidate a structure-activity relationship using scale-bridging techniques such as TEM and electrochemical characterization. The developed based on non-noble electrocatalysts are prepared by a simple method of chemical reduction of transition metal elements with boron in aqueous solution. The production is a one-step process and the material does not require any further treatment, yet this material shows comparable activity to the state of the art (precious metal-based materials) for OER in alkaline solution at a selected current density. This improved catalytic performance is further corroborated by the microstructural investigations in the TEM. The nanoparticles obtained have an improved porous structure compared to Ni–B and thus provide more available sites for the surface reactions and hence for the catalytic performance of the material. Furthermore, it is shown that activation enables the morphological and structural changes, while some transition metal elements act as sacrificial elements to provide more accessible and stable sites for oxygen-forming centers. This paves the way for a better understanding of metal boride-derived electrocatalysts for water oxidation, a crucial chemical reaction in water electrolysis and other electrochemical energy technologies. Acknowledgements: This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 945422. We acknowledge the use of the DFG-funded Micro-and Nanoanalytics Facility (MNaF) at the University of Siegen (INST 221/131-1).

Microwave initiated synthesis of carbon nanosphere from plastic and its application as anode electrocatalyst support in direct methanol fuel cell

The term plastisphere was coined to describe the human-made plastic environment, addressing the challenges of plastic waste. This study presents a rapid method using microwave susceptor catalysts (Co/Mo/Biochar, Ni/Mo/Biochar, Fe/Mo/Biochar) for the catalytic degradation of polystyrene into valuable carbon in microwave synthesizer. Using SEM, we found that active metal nanoparticles are uniformly distributed and the sizes of the active porous sites varied depending upon the catalyst used where the porous active sites of catalyst Co/Mo/biochar, Ni/Mo/biochar and Fe/Mo/biochar ranges between 300 nm and 700 nm, 2.21 μm and 4.05 μm, and 5 μm to larger pore size respectively. The microwave initiated catalytic synthesis process transforms uniform-sized polystyrene pellets into carbon nanospheres within 90 s. From XRD characterization, the broadened peaks at (002) plane resulted from the graphitic flakes' waving structure, confirming that the carbon nanospheres formed are graphitic in nature which is in agreement with results obtained from Raman spectroscopy. This study also explores polystyrene as an energy feedstock, utilizing Co/Mo/Biochar synthesized carbon nanospheres (CNS) which is mesoporous in nature with BET average surface area about 1428.3 m2/g as anode electro catalyst support for methanol oxidation in direct methanol fuel cells. The Pt Ru (1:1) supported on CNS catalyst exhibited higher electro catalytic activity compared to commercial PtRu/C, as indicated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS).

Comparative role of Ag and Ce doping on WO3 and GO modified nanostructures for bi-functional effective photocatalyst and electro catalyst

The comparative study of Ag and Ce doped WO3 modified with GO ternary composites was conducted. Bi-functional promising catalysts were employed for simultaneous Cr (VI) reduction and phenol oxidation as well as hydrogen evolution reaction (HER) through electro catalysis. Both Ag and Ce indicated their effects on orthorhombic WO3. Morphological studies showed big sheets of WO3 were ruptured by foreign materials. C − Ce − W and C − Ag − W surface linkages were analyzed by FTIR and Raman studies. DRS studies indicated that Ce into WO3 alters electronic configuration of WO3. GO/Ag-WO3 showed long absorption tail in visible region. The remarkable quenching of PL intensities is detected in GO/Ag-WO3. GO/Ag-WO3 comparatively produced small onset potential ∼ −175 mV, high current density of ∼75 mAcm−2, small Tafel slop ∼ 46 mV/dec and low charge-transfer resistance (Rct) ∼ 54 Ω. In HER, electronic interaction is strong driving force between WO3 and Ag while GO controls distribution of Ag on WO3/GO leading to fast conduction of charge transfer to improve HER activity. GO/Ag-WO3 composite exhibited elevated photo reduction of Cr (VI) (∼ 86.0 %) and oxidation of phenol (∼ 80.0 %). Trapping test indicated that O2•― and OH• is significant factor for degradation. It provides opportunities of environmentally friendly materials for multipurpose catalytic applications.

Nanoarchitecture of 2D materials: Unveiling the power trio-Ni, Co, and GNF-in eco-friendly air breathing zinc air battery through layered double hydroxides

Zinc-air batteries emerge as sustainable and efficient energy storage device towing to its potential for high energy density and environmental friendliness. Layered double hydroxide (LDH) specifically, exhibit unique properties like high surface area, stability and ion-exchange capacity, making them attractive for various applications. In this work, a simple and scalable one-pot urea hydrolysis process is adopted to synthesize NiCo-LDH supported on graphene nanofiber (GNF) sheets as a good substitute as a non-precious bifunctional catalyst. Ammonium fluoride as a structural-mediating agent is employed which offers a unique homogeneous 3D micro-sized hierarchical petal-like morphology of NiCo-OH. Electrochemical analysis shows low over potential with high durable around 15,000 potential cycles in a 0.5 M KOH solution which confirms the structural integrity and superior activity of NiCo-LDH/GNF catalyst in oxygen reduction and evolution reactions. The resulting NiCo-LDH/GNF composites demonstrate outstanding specific capacitance of 806 mAh g−1 with stable cycling performance up to 950 cycles and rate capability, making it promising alternative bifunctional electro catalyst in Zinc-air batteries.

An innovative method using data acquisition and MATLAB for the electrochemical oxidation of formalin and the conversion of the oxidized products into a sound signal

Abstract Aim: Herein, the oxidation of chemical compounds as sound signals, prepared either by chemical, physical, mechanical, biological methods were reported. Objectives: To fabricate the synthesized material for example, nanoparticle, ceramic, electro catalyst as electrode, by mixing the synthesized material with a suitable binder or they may be mixed with a solvent to function as an electrolyte. In this case, 40 % formalin as electrolyte, platinum and calomel electrode as positive and negative electrodes respectively have been used to formulate an electrochemical cell. Methodology: This cell is connected with the sound card to process the sound signals and analyzed using Sig view software. The sound signals after noise deduction were further processed using MATLAB to get information about the signals. Results: For example, Frequency, Amplitude, etc. of those cells can be obtained. The FFT spectrum obtained by this method correlates well with the FTIR spectrum of formalin. Any Conductive chemical oxidation could be processed in this way and their chemical information could be digitized and saved in cloud.

Unlocking the potential of Heusler alloy Ni2CuSn as an electro(pre)catalyst for enhanced oxygen evolution reaction performance

Unlocking the potential of Heusler alloy Ni2CuSn as an electro(pre)catalyst for enhanced oxygen evolution reaction performance

A Bio‐Inspired Bimetallic Fe−M Catalyst for Electro‐ and Photochemical CO2 Reduction

AbstractThe conversion of CO2 into fuels or commodity chemicals by electrochemical or photochemical reduction is a promising strategy to relieve the ongoing energy crisis and increasing environmental pollution. Inspired by naturally occurring bimetalloenzymes, we have designed hetero–bimetallic CO2 reduction catalysts (FeM) that involve linking an iron tetraphenylporphyrin (FeP) with a tripyridylamine (TPA) moiety, which provides a distal chelating site for Cu2+ or Zn2+. We found that the introduction of Cu2+ or Zn2+ to FeP greatly enhances its efficiency as a catalyst for the electrochemical reduction of CO2. To gain insights into the observed synergistic effect, we performed mechanistic studies together with density functional theory (DFT) calculations. Our results show that Cu2+ or Zn2+ activates CO2 towards reduction due to its Lewis acidity; it also functions as an oxo acceptor from CO2. FeM also functions as an efficient catalyst for the visible‐light‐driven reduction of CO2 using either [Ru(bpy)3] Cl2 or fac‐Ir(ppy)3 (where bpy=2,2’‐bipyridine, ppy=2‐phenylpyridine) as photosensitizer and 1,3‐dimethyl‐2‐phenyl‐2,3‐dihydro‐1H‐benzo[d] imidazole (BIH) as sacrificial reductant. Again, the catalytic efficiency is enhanced by the presence of Cu2+ or Zn2+. Our results provide a general strategy for the design of a series of hetero‐bimetallic catalysts for the reduction of CO2.

Recent advances in the role of MXene based hybrid architectures as electrocatalysts for water splitting.

The development of non-noble metal based and cost-effective electrocatalysts for water splitting has attracted significant attention due to their potential in production of clean and green hydrogen fuel. Discovered in 2011, a family of two-dimensional transition metal carbides, nitrides, and carbonitrides, have demonstrated promising performance as electro catalysts in the water splitting process due to their high electrical conductivity, very large surface area and abundant catalytic active sites. However, their-long term stability and recyclability are limited due to restacking and agglomeration of MXene flakes. This problem can be solved by combining MXene with other materials to create their hybrid architectures which have demonstrated higher electrocatalytic performance than pristine MXenes. Electrolysis of water encompasses two half-cell reactions, hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode. Firstly, this concise review explains the mechanism of water splitting. Then it provides an overview of the recent advances about applications of MXenes and their hybrid architectures as HER, OER and bifunctional electrocatalysts for overall water splitting. Finally, the recent challenges and potential outlook in the field have been presented. This concise review may provide further understanding about the role of MXene-based hybrid architectures to develop efficient electrocatalysts for water splitting.

Evolution of Mn-Bi2O3 from the Mn-doped Bi3O4Br electro(pre)catalyst during the oxygen evolution reaction.

Mn-doped Bi3O4Br has been synthesized using a solvothermal route. The undoped Bi3O4Br and Mn-Bi3O4Br materials possess orthorhombic unit cells with two distinct Bi sites forming a layered atomic arrangement. The shift in the (020) plane in the powder X-ray diffraction (PXRD) pattern confirms Mn-doping in the Bi3O4Br lattice. Elemental mapping indicated 7% Mn doping in the Bi3O4Br lattice structure. A core-level X-ray photoelectron study (XPS) indicates the presence of BiIII and MnII valence-states in Mn-Bi3O4Br. Doping with a cation (MnII) containing a different charge and ionic radius resulted in vacancy/defects in Mn-Bi3O4Br which further altered its electronic structure by reducing the indirect band gap, beneficial for electron conduction and electrocatalysis. The irreversible MnII to MnIII transformation at a potential of 1.48 V (vs. RHE) precedes the electrochemical oxygen evolution reaction (OER). The Mn-doped electrocatalyst achieved 10 mA cm-2 current density at 337 mV overpotential, while the pristine Bi3O4Br required 385 mV overpotential to reach the same activity. The pronounced OER activity of the Mn-Bi3O4Br sample over the pristine Bi3O4Br highlights the necessity of MnII doping. The superior activity of the Mn-Bi3O4Br catalyst over that of Bi3O4Br is due to a low Tafel slope, better double-layer capacitance (Cdl), and small charge-transfer resistance (Rct). The chronoamperometry (CA) study depicts long-term stability for 12 h at 20 mA cm-2. An electrolyzer fabricated as Pt(-)/(+)Mn-Bi3O4Br can deliver 10 mA cm-2 at a cell potential of 2.05 V. The post-CA-OER analyses of the anode confirmed the leaching of [Br-] followed by in situ formation of Mn-doped Bi2O3 as the electrocatalytically active species. Herein, an ultra-low Mn-doping into Bi3O4Br leads to an improvement in the electrocatalytic performance of the inactive Bi3O4Br material.

A Soft Molecular Single-Source Precursor Approach to Nanostructured Co9S8 (Pre)Catalyst for Efficient Water Oxidation and Biomass Valorization

The molecular single-source precursor (SSP) route emerges as a promising avenue for synthesizing highly efficient electro(pre)catalysts tailored for both oxygen evolution (OER) and organic electrooxidation reactions. This study introduces a...

Elucidation of the Interplay between the Features of the Precursor and the Physicochemical Properties of “Core-Shell” Hierarchical Carbon Nitride Electrocatalysts for the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is a major bottleneck in the operation of proton-exchange membrane fuel cells (PEMFCs) since it introduces large overpotentials (no less than 250-300 mV), which degrade significantly the energy conversion efficiency of the device. In addition, the electrocatalysts (ECs) yielding the lowest ORR overpotentials in the acidic environment found at the PEMFC cathode are based on Pt, a very scarce critical raw material (CRM). Pt raises concerns as it might trigger serious supply bottlenecks in the event of a practical widespread implementation of PEMFCs in the framework of today’s energy transition. Hence, the development of high-performing and durable ECs for the ORR is a major stepping stone towards the large-scale rollout of PEMFCs.In our research group a new breakthrough approach has been devised for the synthesis of ORR ECs, that is completely different form the preparation routes that are commonly adopted in the state of the art [1, 2]. Briefly, the approach consists in the pyrolysis and subsequent treatment of a precursor obtained by coupling suitable carbon species/sacrificial supports with a zeolitic inorganic-organic polymer electrolyte (Z-IOPE). The latter comprises anionic complexes including the Pt “catalyst” and other “co-catalysts”, which are bridged by organic binders [1,2].On one hand, the proposed approach has already shown its potential to yield ECs exhibiting a performance and durability improved with respect to Pt/C benchmark ECs. On the other hand, the proposed approach is extremely flexible, especially with respect to the synthesis of the initial EC precursor. In principle, it is possible to modulate a number of crucial features of such EC precursor, with a particular reference to: (i) the chemical composition (e.g., in terms of Pt, other “co-catalysts” and N; the latter plays a crucial role to stabilize the active sites into “coordination nests” on the EC surface, raising durability); and (ii) the morphology, that can be “templated” on suitable species (e.g., carbon species, sacrificial supports). The very flexibility of the proposed synthetic process needs to be leveraged appropriately to maximize the performance of the final ORR ECs, at the same time minimizing the efforts wasted on approaches with a low development potential.Herein it is elucidated how the modulation in the parameters involved in the synthesis of the EC precursor (e.g., the binder and the approaches to couple the Z-IOPE with the support) impact the physicochemical and electrochemical properties of the final ECs, with a particular reference to the chemical composition, morphology and distribution of the ORR active sites. An extensive characterization of the final ECs is carried out. Inductively-coupled plasma atomic emission spectroscopy (ICP-AES) and microanalysis are adopted to determine the bulk chemical composition. Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is used to elucidate the surface chemical composition and the chemical states of the surface elements. Ultra-high resolution scanning electron microscopy (UHR-SEM) and transmission electron microscopy (TEM) allow for the elucidation of EC morphology. The porosimetric features are probed by automatic gas adsorption instrumentations. Wide-angle X-ray diffraction (WAXD) is crucial to resolve the crystal structure. Cyclic voltammetry with the rotating ring-disk electrode method (CV-TF-RRDE) is used to clarify the “ex-situ” electrochemical performance and ORR reaction mechanism. Finally, the most promising ECs are used in the fabrication of single PEMFCs, that are tested as a function of the operating conditions.It is revealed that, in comparison with the Pt/C benchamark, some ECs are characterized by a much higher intrinsic kinetic performance due to the electronic and bifunctional effects bestowed by the carbon nitride support and the «co-catalysts». Finally, the binder has a marked effect on the stoichiometry, size, and distribution of the PtMx aggregates bearing the active sites.

Electrochemical Analysis on Transition Metal Nitride Catalysts for Nitrogen Reduction Reaction

A versatile and sustainable process for ammonia production is needed to ensure a sustainable future for the growing global population, both with regards to fertilizer production as well as energy carrier. Theoretical simulations of transition metal nitride catalysts have demonstrated the possibilityof a nitrogen reduction reaction catalysis cycle on four transition metal nitrides, CrN, VN, ZrN and NbN.[1,2] Reproducible and reliable research and development approaches in the direction of electrochemical reduction of nitrogen towards ammonia are therefore of importance. An operando ammonia quantification methodology for electrochemical catalysis studies has been developed in-house and recently published [3]. Allowing for automatic, quantitative detection of aqueouos ammonia at the ppb level, within minutes from the sample preparation. We have now analyzed all four theoretically proposed TMNs, as well as rutile Niobium oxynitride (NbON) of several stochiometries as thin films on a conductive electrode substrate in ambient environment and aqueouos electrochemical system [3,4].Electrochemical analysis and ammonia quantification suggest NbON of specific stochiometry and ZrN to be promising catalyst candidates, while lacking stability in the environment of choice in these studies.Literature:[1] Y. Abghoui, A.L. Garden, J.G. Howalt, T. Vegge and E. Skúlason, Electroreduction of N2 to ammonia at ambient conditions on mononitrides of Zr, Nb, Cr, and V: A DFT guide for experiments. ACS Catalysis, 2016.6(2): p. 635.[2] Y. Abghoui, A.L. Garden, V.F. Hlynsson, S. Björgvinsdóttir, H. Ólafsdóttir and E.Skúlason, Enabling electrochemical reduction of nitrogen to ammonia at ambient conditions through rational catalyst design. Physical Chemistry Chemical Physics,2015.17(7): p. 4909.[3] F. Hanifpour, C.P. Canales, E.G. Fridriksson, A. Sveinbjörnsson, T.K. Tryggvason,E. Lewin, . H.D. Flosadóttir, Investigation into the mechanism of electrochemical nitrogen reduction reaction to ammonia using niobium oxynitride thin-film catalysts. Electrochimica Acta, 2022.403: p. 139551.[4] F. Hanifpour, C.P. Canales, E.G. Friðriksson, A. Sveinbjörnsson, T. Tryggvason, Y.Abghoui, . E. Skúlason, Operando Quanitification of ammonia produced from computationally derived transition metal nitride electro catalysts. Journal of Catalysis, 2022. 413: p.956

Synergistic catalytic effect of fluorine coordination in defects engineered nitrogen-doped 3D-Hierarchical Zn polymer-derived carbon as efficient bifunctional electrocatalysts

Metal-free electrocatalysts for Hydrogen evolution reaction (HER) and Oxygen evolution reaction (OER) are highly desirable alternatives to expensive metal electrocatalysts. Herein, two metal-free heteroatom doped electro catalysts PCF-800 (carbon doped with fluorine) and PCFN-800 (carbon co-doped with nitrogen and fluorine) have been derived from the pyrolysis of ZnTFBDC and ZnTFBDC(1,10phen) accordingly. Both showed stunning performance for HER and OER in comparison with commercially available multiwall Nano carbon tubes. The graphitic and pyridinic carbon sites are generated in PCF-800 and PCFN-800 during the thermal polymerization process. These catalytic sites are responsible for excellent activity in terms of overpotential and Tafel slopes for HER process. Synthesized catalysts showed HER activities that are comparable to commercially available 20%Pt/C. PCFN-800 showed stability for about 30 h with a little decrease in current. Moreover, the mechanistic approach for HER and OER theoretical work was done and it has been found that the ΔG*H value for PCFN-800 is 0.51 eV that is less than 0.71 eV for N-doped carbon material for HER process.

Intermetallic FeNiAs as an Electro(pre)catalyst for Enhanced Electrochemical Water Oxidation

Intermetallic FeNiAs as an Electro(pre)catalyst for Enhanced Electrochemical Water Oxidation

Interfacial engineering of α-Fe2O3 coupled Co3O4 heterostructures anchored on g-C3N4 structure for enhanced electrocatalytic performance in alkaline oxygen evolution reaction

Creating an efficient electrocatalytic oxygen evolution reaction (OER) by developing a low-cost, stable metal oxide nanocomposite based on earth-abundant materials is an essential and highly efficient method to meet the increasing demand for sustainable energy. For this reason, we have proposed a simple and effective interfacial engineering approach to construct a novel graphitic carbon nitride (g-C3N4) strongly coupled with α-Fe2O3 and Co3O4 as dual co-catalysts for highly active electrocatalysts (ECs) OER in a typical alkaline electrolyte. The detailed structural, chemical, and morphological characterizations were performed by various analyses. The as-synthesized g-C3N4/Co3O4/α-Fe2O3 (GCFO) nanocomposite ECs exhibited efficient and stable OER performances with low overpotentials of 359 mV to attain a 10 mA/cm2 current density and a less Tafel slope of 116 mV dec−1, resulting in better durability after 14 h of the i-t test. A strong coupling interaction was found at the interface between the g-C3N4 and the α-Fe2O3/Co3O4 heterostructure, which acts as an effective electron transport channel and exposes more catalytically active sites to explore the outstanding performances for electrocatalysis OER. These results show that a novel approach for the rational coupling of composite heterostructures could be an alternative to using noble metals for sustainable energy-related applications.

Investigation of improved Bifunctional electrocatalytic HER and OER performances of Lanthanum Molybdate supported Graphene oxide composite in Acidic and Alkaline media

Developing low-cost and high-performance emergent bifunctional electrocatalysts (ECs) is crucial to catalyze the overall electrocatalytic water-splitting. In this work, Lanthanum Molybdate (LaM) in the graphene oxide (GO) surface to develop its electrocatalytic applications in various environments is designed and presented. LaM/GO ECs could enhance the HER catalytic efficiency with a less overpotential of −0.21 V and less Tafel slope value of 81 mV dec−1 at an optimum current density of 10 mA cm−2 on typical acid media. Also, the less Tafel slope of 186 mV dec−1 and less overpotential (0.56 V) for catalyzing OER in alkaline media signifies its bifunctional electrocatalytic HER and OER activity. Moreover, it could exhibit admirable durability after 5000 cycles in both alkaline and acidic media. The outstanding bifunctional electrochemical activity of LaM/GO might be accredited to the novel construction method and benefits of LaM not only facilitates electron transfer but also interacts with the GO layer surface to make a synergic catalytic effect and might offer a large electrochemical surface area. Hence, this present work could be prolonged to propose and fabricate these sequence composites with the advantage of bifunctional catalysts for practical water-splitting applications.

(Keynote) Interplay between Physicochemical Properties of Precursors and “Core-Shell” Hierarchical Carbon Nitride Electrocatalysts for the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is a major bottleneck in the operation of proton-exchange membrane fuel cells (PEMFCs) since it introduces large overpotentials (no less than 250-300 mV), which degrade significantly the energy conversion efficiency of the device. In addition, the electrocatalysts (ECs) yielding the lowest ORR overpotentials in the acidic environment found at the PEMFC cathode are based on Pt, a very scarce critical raw material (CRM). Pt raises concerns as it might trigger serious supply bottlenecks in the event of a practical widespread implementation of PEMFCs in the framework of today’s energy transition. Hence, the development of high-performing and durable ECs for the ORR is a major stepping stone towards the large-scale rollout of PEMFCs.In our research group a new breakthrough approach has been devised for the synthesis of ORR ECs, that is completely different form the preparation routes that are commonly adopted in the state of the art [1, 2]. Briefly, the approach consists in the pyrolysis and subsequent treatment of a precursor obtained by coupling suitable carbon species/sacrificial supports with a zeolitic inorganic-organic polymer electrolyte (Z-IOPE). The latter comprises anionic complexes including the Pt “catalyst” and other “co-catalysts”, which are bridged by organic binders [1,2].On one hand, the proposed approach has already shown its potential to yield ECs exhibiting a performance and durability improved with respect to Pt/C benchmark ECs. On the other hand, the proposed approach is extremely flexible, especially with respect to the synthesis of the initial EC precursor. In principle, it is possible to modulate a number of crucial features of such EC precursor, with a particular reference to: (i) the chemical composition (e.g., in terms of Pt, other “co-catalysts” and N; the latter plays a crucial role to stabilize the active sites into “coordination nests” on the EC surface, raising durability); and (ii) the morphology, that can be “templated” on suitable species (e.g., carbon species, sacrificial supports). The very flexibility of the proposed synthetic process needs to be leveraged appropriately to maximize the performance of the final ORR ECs, at the same time minimizing the efforts wasted on approaches with a low development potential.Herein it is elucidated how the modulation in the parameters involved in the synthesis of the EC precursor (e.g., the binder and the approaches to couple the Z-IOPE with the support) impact the physicochemical and electrochemical properties of the final ECs, with a particular reference to the chemical composition, morphology and distribution of the ORR active sites. An extensive characterization of the final ECs is carried out. Inductively-coupled plasma atomic emission spectroscopy (ICP-AES) and microanalysis are adopted to determine the bulk chemical composition. Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is used to elucidate the surface chemical composition and the chemical states of the surface elements. Ultra-high resolution scanning electron microscopy (UHR-SEM) and transmission electron microscopy (TEM) allow for the elucidation of EC morphology. The porosimetric features are probed by automatic gas adsorption instrumentations. Wide-angle X-ray diffraction (WAXD) is crucial to resolve the crystal structure. Cyclic voltammetry with the rotating ring-disk electrode method (CV-TF-RRDE) is used to clarify the “ex-situ” electrochemical performance and ORR reaction mechanism. Finally, the most promising ECs are used in the fabrication of single PEMFCs, that are tested as a function of the operating conditions.It is revealed that, in comparison with the Pt/C benchamark, some ECs are characterized by a much higher intrinsic kinetic performance due to the electronic and bifunctional effects bestowed by the carbon nitride support and the «co-catalysts». Finally, the binder has a marked effect on the stoichiometry, size, and distribution of the PtMx aggregates bearing the active sites.