Non-precious Metal Oxygen Reduction Reaction Research Articles

Boosting Zn-air battery performance: Fe single-atom anchored on F, N co-doped carbon nanosheets for efficient oxygen reduction

Sluggish oxygen reduction reaction (ORR) kinetics limit the development of metal-air batteries and fuel cells, hindering overall energy conversion efficiency. Therefore, significant research has focused on cost-effective, highly active, and exceptionally stable non-precious metal ORR electrocatalysts. This study presents the synthesis of a nanohybrid material called Fe SAs/FN-CNs. It is made up of single iron atoms embedded in ultrathin porous carbon nanosheets that are co-doped with F and N. The synthesis process involves an easy one-step pyrolysis technique without additional post-treatment. The Fe SAs/FN-CNs material is designed to function as an effective zinc-air battery ORR electrocatalyst. Based on their distinctive components and structure, the optimal Fe SAs/FN-CNs exhibit outstanding catalytic efficiency and long-lasting performance in the alkaline ORR. They have an onset potential (Eonset) of 0.95 V, a half-wave potential (E0.5) of 0.85 V, a kinetic current density (JK) of 20.49 mA cm−2 at 0.8 V, and a diffusion-limited current (Jd) of 6.2 mA cm−2. In addition, a Zn-air battery made using homemade Fe SAs/FN-CNs demonstrated a power density of 197 mW cm−2, a specific capacitance of 813.5 mAh g−1, and exceptional stability. It outperformed the commercial Pt/C by operating continuously for over 147 hours at 10 mA/cm² (discharge-charge). The Fe SAs/FN-CNs nanohybrid electrocatalyst shows great potential as an electrocatalyst for various metal-air batteries.

A lignin–derived N-doped carbon-supported iron-based nanocomposite as high-efficiency oxygen reduction reaction electrocatalyst

Fuel cells are a promising renewable energy technology that depend heavily on noble metal Pt-based catalysts, particularly for the oxygen reduction reaction (ORR). The discovery of new, efficient non-precious metal ORR catalysts is critical for the continued development of cost-effective, high-performance fuel cells. The synthesized carbon material showed excellent electrocatalytic activity for the ORR, with half-wave potential (E1/2) and limiting current density (JL) of 0.88 V and 5.10 mA·cm−2 in alkaline electrolyte, respectively. The material has a Tafel slope of (65 mV dec−1), which is close to commercial Pt/C catalysts (60 mV dec−1). Moreover, the prepared materials exhibited excellent performance when assembled as cathodes for zinc-air batteries. The power density reached 110.02 mW cm−2 and the theoretical specific capacity was 801.21 mAh g−1, which was higher than that of the Pt/C catalyst (751.19 mAh g−1). In this study, with the assistance of Mg5(CO3)4(OH)2·4H2O, we introduce an innovative approach to synthesize advanced carbon materials, achieving precise control over the material's structure and properties. This research bridges a crucial gap in material science, with potential applications in renewable energy technologies, particularly in enhancing catalysts for fuel cells.

Water hyacinth root derived hybrid metal oxides/nitrogen doped porous carbon as an efficient non-precious metal oxygen reduction reaction electrocatalyst in alkaline media

A biomass derived hybrid metal oxides/nitrogen doped porous carbon (NC) electrocatalyst is fabricated by direct pyrolysis of the water hyacinth root (WHR) mixed ZnCl2 raw materials at 600 °C (WHR600), 700 °C (WHR700) and 800 °C (WHR800) under autogenic pressure conditions. XRD analysis presents a novel Zn(Al1.8Fe0.2)O4 compound combined with hematite quart and muscovite phases for WHR700 and WHR800 samples. In addition, the WHR700 sample accounts for the maximum pyridinic N content incorporated into carbon framework (NC). Electrochemically, the WHR700 catalyst displays the highest oxygen reduction reaction (ORR) performance in alkaline media. The high ORR performance for WHR700 catalyst is significantly a result of the presence of the Zn(Al1.8Fe0.2)O4 phase and the pyridinic N species. Furthermore, an accelerate durability test for WHR700 sample over 5000 cycles exhibits only 8 mV half-wave potential reduction. The WHR700 catalyst is also extremely stable to the methanol poisoning during ORR operation.

Co3Fe7/CoCx nanoparticles encapsulated in nitrogen-doped carbon nanotubes synergistically promote the oxygen reduction reaction in Zn-air batteries

Efficient and stable non-precious metal catalysts (NPMCs) for the oxygen reduction reaction (ORR) are crucial for the advancement of Zn-air batteries. Herein, we report a supramolecular self-scarifying template and confinement pyrolysis strategy to obtain an efficient ORR catalyst of well-dispersed Co3Fe7/CoCx heterostructure nanoparticles encapsulated by nitrogen-doped carbon nanotubes (Co3Fe7/CoCx@N-CNT). The as-synthesized Co3Fe7/CoCx@N-CNT catalyst exhibited outstanding ORR activity, with a half-wave potential of 0.88 V versus a reversible hydrogen electrode, and good stability. The Zn-air battery based on the Co3Fe7/CoCx@N-CNT cathode achieved a peak power density of 265 mW cm−2 and a durability of over 200 h, which is superior to most reported NPMCs and even the Pt/C counterpart. The physical characterization and electrochemical poisoning experiments revealed that the Co3Fe7/CoCx nanoparticles in the core along with pyridine N and Fe–Nx hosted in the carbon nanotube all acted as active sites for the ORR. Further theoretical calculations showed that the charge redistribution between the Co3Fe7/CoCx nanoparticles and the Fe–Nx carbon overlayers downshifted the d-band center of Fe and optimized the adsorption ability, which boosted the ORR kinetics. This work provides an effective strategy to synthesize non-precious metal ORR catalysts with multiple active sites and highlights the synergistic role of encapsulated nanoparticles and carbon support.

Fe&Fe2O3 Dual-Decorated on N-Doped Porous Carbon for Oxygen Reduction Reaction

Catalysts for the cathodic oxygen reduction reaction (ORR) are important in fuel cells. Herein, a class of non-precious metal ORR catalyst, namely Fe&Fe2O3 dual-decorated on N-doped porous carbon (Fe&Fe2O3/NC), is prepared from the pyrolysis of a mixture containing Fe2O3/NC, Fe salt and melamine, followed by acid-leaching, where Fe2O3/NC is firstly synthesized from one-step pyrolyzing the precursors of coal, KOH, melamine and Fe salt. As a result, the Fe&Fe2O3/NC provides a much better ORR catalytic activity with the peak potential (Ep) and half-wave potential (E1/2) of 902 mV and 852 mV, respectively, than these of Fe2O3/NC (824 mV and 768 mV) and close to these of 20 wt% commercial Pt/C (918 mV and 863 mV). Furthermore, the ORR occurred on Fe&Fe2O3/NC follows near a four-electron transfer pathway. It also has a good stability and methanol-resistance. By comparing the structures of Fe2O3/NC and Fe&Fe2O3/NC, the essential roles on improving the ORR catalytic activity are discussed: both the abundant graphitic N active sites and the synergistic effect of Fe and Fe2O3 play important roles. This work not only provides a general guideline for the design and development of non-precious metal-based catalysts for ORR but also enriches the application scope of coal.

Se Atom Doping Enhances the Catalytic Activity of Co@NC for Oxygen Reduction Reaction

As the most promising nonprecious metal oxygen reduction reaction (ORR) catalyst, Co@NC catalysts have attracted much attention. Herein, to further improve the activity of Co@NC catalysts, Co and Se atoms are embedded in metal organic framework‐derived nitrogen‐doped porous carbon (NC) using a high‐temperature reduction strategy, and then Co–Se@NC catalysts are constructed. The ORR catalytic activity of the catalysts is evaluated by rotating disc electrodes, and the results show that the ORR catalytic activity of the Co–Se@NC catalysts is significantly enhanced compared to the Co@NC and Se@NC catalysts, demonstrating that the introduction of Se atoms into Co@NC catalysts can significantly improve the ORR catalytic activity. Spectral characterization and pore size analysis shows that the introduction of Se atoms has multiple effects, including providing new active sites, improving the pore structure of the catalyst, and promoting electron transfer and mass transport. This study shows that the Co–Se@NC catalysts has excellent catalytic performance for ORRs, reaching half‐wave potentials of 0.765 V in acidic electrolytes and 0.831 V in alkaline electrolytes, demonstrating that the introduction of Se atoms can effectively improve the ORR catalytic activity, thus providing a unique insight into the rational construction of ORR catalysts.

Increasing Accessible Active Site Density of Non-Precious Metal Oxygen Reduction Reaction Catalysts through Ionic Liquid Modification.

Non-precious metal catalysts show great promise to replace the state-of-the-art Pt-based catalysts for catalyzing the oxygen reduction reaction (ORR), while their catalytic activity still needs to be greatly improved before their broad-based application. Here, we report a facile approach to improving the performance of zeolitic imidazolate framework-derived carbon (ZDC) toward the ORR by incorporating a small amount of ionic liquid (IL). The IL would preferentially fill the micropores of ZDC and greatly enhance the utilization of the active sites within the micropores, which are initially not accessible due to insufficient surface wetting. It is also disclosed that the ORR activity in terms of kinetic current at 0.85 V depends on the loading amount of the IL, and the maximum activity is obtained at a mass ratio of IL to ZDC at 1.2. The optimum stems from the counterbalance between the enhanced utilization of the active sites within the micropores and the retarded diffusion of the reactants within the IL phase due to its high viscosity.

Co/Co2N/N/C oxygen reduction reaction catalysts derived from sisal fiber porous carbon and cobalt phthalocyanine

Sisal fibers (SF) were used as carbon source for their long and uniform multiporous structure. The composite Co/Co2N/N/C catalysts by pre-activation SF porous carbon (SPC) and cobalt phthalocyanine (CoPc) were prepared by high-temperature pyrolysis and precise control of the composite proportion of SPC and CoPc. The catalyst treated with a composite proportion of SPC and CoPc of 1 to 4 (SPC@CoPc-1-4) exhibited high Eonset potential of 1.04 V, high stability of 90.50 %, and slightly lower E1/2 of 5 mV than Pt/C (20 wt%) catalyst. Considering the performance and price of catalysts in practical application, these composite catalysts combining biomass carbon materials and phthalocyanine series will be provide a valuable reference for non-precious metal oxygen reduction reaction (ORR) catalysts.

Multicore-shell structure CuxCoy-Fe alloy nitrogen doped mesoporous hollow carbon nanotubes composites for oxygen reduction reaction

Carbon-based materials with transition metal modifications are the dominant materials for oxygen reduction reaction (ORR), but the synthesis in a simple and efficient way is still a great challenge. Herein, multicore-shell structure CuxCoy-Fe alloy nitrogen doped mesoporous hollow carbon nanotubes (N-MHCNT/CuxCoy-Fe@C) were designed and synthesized by a facile and environment-friendly method. In the process of pyrolysis, polypyrrole serving as the substrate to form N-doped hollow carbon nanotubes and the polydopamine (PDA) acts as the carbon and nitrogen source to form a shell structure. Additionally, the cubic CuxCoy-Fe MOFs synthesized at room temperature collapses to form multiple alloy cores. Notably, the mesoporous structure of N-MHCNT/CuxCoy-Fe@C enhances the mass transfer process, while the carbon shell protects the metal active sites. Moreover, mesoporous hollow carbon, rich M-Nx (M=Cu, Co, Fe) active sites, the synergistic effects between N-MHCNTs, CuxCoy-Fe alloys and multiple core-shell structures allowed N-MHCNT/Cu2Co1-Fe@C exhibited high activity and long-term durability in ORR. Besides, the RRDE tests confirms the reaction kinetics of N-MHCNT/Cu2Co1-Fe@C as a mainly 4-electron reaction with an electron transfer number of 3.78 (Pt/C is 3.86) and a low hydrogen peroxide yield of 16%. This work provides a new strategy for the development of non-precious metal ORR catalysts by rational structural design and metal ratio adjustment.

The synergistic effect of “soft-hard template” to in situ regulate mass transfer and defective sites of doped-carbon nanostructures for catalysis of oxygen reduction

Nitrogen-doped carbon materials are intensively investigated as electrocatalysts toward oxygen reduction reaction (ORR). The activity of the catalysts can be effectively boosted by regulating the microstructure to construct defective three-phase interface. Herein, an N-doped carbon-based porous catalyst (DT-Fe-N-C) is fabricated by a dual-template strategy with SiO2 and pluronic F127 as the hard and soft templates. Benefited from the modulation, the mesopore-dominated DT-Fe-N-C exhibits remarkable specific surface area (990.19 m2 g-1), high Fe-Nx content and plenty of defects. Resultantly, DT-Fe-N-C shows outstanding catalytic activity to ORR with 0.853 V of half-wave potential, high stability and selectivity to the four-electron ORR mechanism. The Zn-air battery with DT-Fe-N-C outputs 219 mW cm-2 of maximum power density, 861 Wh kgZn−1 of specific energy density at 50 mA cm-2 and runs at a higher voltage than that of Pt/C-based battery. This work provides an avenue for the defect engineering in the design of non-precious metal ORR catalysts.

Si Doping Enables Activity and Stability Enhancement on Atomically Dispersed Fe-Nx /C Electrocatalysts for Oxygen Reduction in Acid.

Fe-N-C represents the most promising non-precious metal catalysts (NPMCs) for the oxygen reduction reaction (ORR) in fuel cells, but often suffers from poor stability in acid due to the dissolution of metal sites and the poor oxidation resistance of carbon substrates. In this work, silicon-doped iron-nitrogen-carbon (Si/Fe-N-C) catalysts were developed by in situ silicon doping and metal-polymer coordination. It was found that Si doping could not only promote the density of Fe-Nx /C active sites but also elevated the content of graphitic carbon through catalytic graphitization. The best-performing Si/Fe-N-C exhibited a half-wave potential of 0.817 V vs. reversible hydrogen electrode in 0.5 m H2 SO4 , outperforming that of undoped Fe-N-C and most of the reported Fe-N-C catalysts. It also exhibited significantly enhanced stability at elevated temperature (≥60 °C). This work provides a new way to develop non-precious metal ORR catalysts with improved activity and stability in acidic media.

Iron Single Atoms Anchored on Nitrogen-Doped Carbon Matrix/Nanotube Hybrid Supports for Excellent Oxygen Reduction Properties

Single-atom non-precious metal oxygen reduction reaction (ORR) catalysts have attracted much attention due to their low cost, high selectivity, and high activity. Herein, we successfully prepared iron single atoms anchored on nitrogen-doped carbon matrix/nanotube hybrid supports (FeSA-NC/CNTs) by the pyrolysis of Fe-doped zeolitic imidazolate frameworks. The nitrogen-doped carbon matrix/carbon nanotube hybrid supports exhibit a specific surface area of 1626.814 m2 g−1, which may facilitate electron transfer and oxygen mass transport within the catalyst and be beneficial to ORR performance. Further electrochemical results revealed that our FeSA-NC/CNTs catalyst exhibited excellent ORR activity (half-wave potential: 0.86 V; kinetic current density: 39.3 mA cm−2 at 0.8 V), superior to that of commercial Pt/C catalyst (half-wave potential: 0.846 V; kinetic current density: 14.4 mA cm−2 at 0.8 V). It also has a great stability, which makes it possible to be a valuable non-noble metal electrode material that may replace the latest commercial Pt/C catalyst in the future.

ZIF-67-derived Co nanoparticles embedded in N-doped porous carbon composite interconnected by MWCNTs as highly efficient ORR electrocatalysts for a flexible direct formate fuel cell

Non-precious metal materials are considered as the most promising catalysts for oxygen reduction reaction (ORR) due to their high catalytic activity, low cost, superior stability as well as good electrocatalytic selectivity. Here, in situ encapsulation of Co nanoparticles into N-doped porous carbon ([email protected]) nanocages interconnected by carbonized multi-walled carbon nanotubes (C-MWCNTs) are prepared through direct carbonization of the MWCNTs-based ZIF-67 precursor. The obtained hybrid material (denoted as [email protected]/C-MWCNTs) displays an excellent ORR performance with a half-wave potential of 0.79 V, effective four-electron transfer and superior formate-tolerance ability. The superior ORR activity of the [email protected]/C-MWCNTs hybrids is mainly ascribed to the abundant catalytic active sites contributed by the [email protected] nanocages, the high electrical conductivity and large specific surface area rooting in C-MWCNTs, and synergetic effects between [email protected] nanocages and C-MWCNTs. The membraneless flexible direct formate fuel cell (DFFC) using [email protected]/C-MWCNTs as the cathode catalyst delivers a peak power density of 4.32 mW cm−2 stably. Notably, the performance of the flexible DFFC can still maintain 90.9% of its initial value after repeated bending for 1000 times. Moreover, two flexible DFFCs connected in series mode can easily power some low-power electronics. The report not only opens a new door to design high-performance non-precious metal ORR catalysts for DFFCs, but also greatly boosts the development of flexible energy conversion and storage devices.

Application of rock-salt-type Co–Mn oxides for alkaline polymer electrolyte fuel cells

Co–Mn oxides are a group of highly effective non-precious metal oxygen reduction reaction (ORR) catalysts for alkaline polymer electrolyte fuel cells (APEFCs). Despite being widely studied in alkaline solutions, limited studies of them have been developed in APEFCs. In this work, we evaluate the performance of a rock-salt-type Co–Mn composite oxides (CoMnO 2 /C) in both alkaline solution and APEFCs. Other than that, we also test its durability in APEFCs and investigate its degradation mechanism. CoMnO 2 /C exhibits a high ORR activity in both rotate disk electrode (RDE) study and APEFCs test. The ORR half-wave potential is 0.86 V in 1 M KOH, and the peak power density (PPD) reaches 1.2 W/cm 2 in H 2 –O 2 APEFCs when using PtRu as anode. In air (CO 2 -free) condition, APEFC reaches a PPD of 0.83 W/cm 2 , and can operate over 40 h at a constant current density of 200 mA/cm 2 . Further experiments reveal that the cell performance degradation can be ascribed to the dissolution and valence increase of Mn from +3 to +3.6 on the catalysts surface. • CoMnO 2 /C exhibits high performance in both alkaline solution and APEFCs. • In air (CO 2 -free) condition, CoMnO 2 /C reaches a PPD of 0.83 W/cm 2 . • APEFCs using CoMnO 2 /C cathode can operate over 40 h at 200 mA/cm 2 . • Cell performance degradation is due to the dissolution and valence increase of Mn.

Deep-breathing Fe-doped superstructure modified by polyethyleneimine as oxygen reduction electrocatalysts for Zn–air batteries

The development of economical, robust and highly active non-precious metal oxygen reduction reaction (ORR) electrocatalysts to replace precious metal catalysts is crucial for the widespread applications of metal–air batteries.

A Simple Synthesis of Fe2P Nanoparticles Encapsulated Doped Carbon Nanotube as Electrocatalysts for Oxygen Reduction Reaction and Zinc‐Air Battery

The design and application of high efficiency, low cost, and nonprecious metal oxygen reduction reaction (ORR) catalyst is a prerequisite for the commercialization of energy conversion devices. Here, a simple method is proposed to prepare Fe2P nanoparticles encapsulated in nitrogen‐doped carbon nanotubes (Fe2P@NPCNTs) through a self‐growth strategy. In addition, it is worth noting that Fe2P@NPCNTs have high catalytic activity and good stability as ORR catalysts due to the unique structure of the material, the synergy between the components, and the large specific surface area. As expected, the catalyst has a half‐wave potential (0.827 V) close to commercial Pt/C and a lower Tafel slope (54.17 mV dec−1) compared to other samples. Meanwhile, the zinc‐air battery with Fe2P@NPCNTs as catalysts exhibits high open‐circuit voltage, good maximum power density, and excellent stability. Therefore, this cheap and simple method is generally available for the synthesis of other non‐noble metal catalysts for various energy systems.

Progress in non-noble metal oxygen reduction electrocatalysts based on MOFs

<p indent=0mm>Proton exchange membrane fuel cells (PEMFCs) are favored in the field of new energy vehicles because of their cleanliness, high efficiency, quietness, high power density, low operating temperature, fast start-up and power matching. With the realization of mass production of fuel cell vehicles in many countries in the world in recent years, its large-scale promotion is imperative. However, the PEMFC cathode uses a high-load platinum (Pt)-based catalyst, which has greatly hindered the commercialization of fuel cell vehicles because of high cost. Pt is the most effective electrocatalyst for the low-temperature fuel cell cathode oxygen reduction reaction (ORR). On one hand, it can greatly reduce the amount of Pt through alloying and single-atom layer design. On the other hand, it can develop alternative high-activity and high-stability non-noble metals. The catalyst process is considered the ultimate solution. Among the many types of non-noble metal catalysts, the ORR activity and lifetime of the carbon-nitrogen-transition metal series non-noble metal catalysts are particularly worthy of attention. Non-precious metal ORR electrocatalysts based on metal organic framework materials (MOFs) have been extensively studied for their excellent properties. This paper introduces the characteristics and advantages of MOFs materials in detail and reviews the research status of carbon-nitrogen-transition metal ORR electrocatalysts based on MOFs materials at home and abroad in recent years, including Fe-based MOFs catalysts, Co-based MOFs catalysts, and bimetal MOFs catalysts. It also analyzes and forecasts the bottlenecks and challenges encountered in the research. In the future, we need to conduct in-depth research on the activity and stability of membrane electrodes.

Theoretical insights for CoNxC4-x-graphene (x = 0–4) materials as high performance low-cost electrocatalysts for oxygen reduction reactions

Transition metal-doped two-dimension carbon matrices have attracted particular interest as oxygen reduction reaction (ORR) catalysts because of their low-cost, good conductivity of electricity, and promising applications in fuel cells and metal-air batteries. Herein, a density functional theory study is performed on the CoNxC4-x (x = 0–4) embedded graphene to investigate the effect of N atoms doping number and doping configurations. The calculated formation energy and average bond length of Co–C/N drop off with the increase in N atoms of the CoNxC4-x graphene system. The most stable adsorption configurations and the relevant adsorption free energies of key ORR intermediates on Co–N sites toward the CoNxC4-x graphene system are obtained, indicating that N doping levels and doping configurations have a regular influence on this system. On this basis, scaling relations can be obtained among the adsorption free energies of *OH, *OOH, and *O. The volcano plot of ORR theoretical overpotential (ηth) using ΔG*OH−ΔG*O as a descriptor was further established, which revealed that ηth is influenced by the adsorption mode and the free energy change in the active site. For all studied systems, the ORR substeps are all downhill at zero potential from the plotted free energy diagrams. The density of states is employed to further illustrate that the hybridization between the Co atom and the O atom is a deterring factor on electrocatalyst activity. These calculations reveal the influence of nitrogen atom doping in Co–N-graphene catalysts and afterward point a direction for designing high-performance non-precious metal ORR electrocatalysts.

Designed Synthesis and Catalytic Mechanisms of Non-Precious Metal Single-Atom Catalysts for Oxygen Reduction Reaction.

Oxygen reduction reaction (ORR) is the important half-reaction for metal-air batteries and fuel cells (FCs), which plays the decisive role for the performance of whole devices. Developing high-efficiency non-precious metal ORR catalysts is urgent and still challenging. Single-atom catalysts (SACs) are considered to be one of the promising substitutes for Pt due to their maximum atom utilization efficiency and mass activity. Despite considerable efforts in preparing various SACs, the reaction mechanism and intrinsic activity modulation during the ORR reaction are still not understood in-depth. In this review, the latest advances in the current synthetic strategies for SACs are summarized. The effect of various coordination environments including central metal atoms, coordination atoms, environmental atoms, and guest groups on the intrinsic ORR activity of SACs are discussed. The electrocatalytic mechanisms are clarified by combining density functional theory calculations with in situ advanced characterization technologies. Then, the applications of SACs in FCs and Zn-air batteries are reviewed. Finally, the prospects and challenges for further development of SACs are highlighted.

Catalysts Containing Transition Metals on Nitrogen and Carbon Structures for Hydrogen Production through Salt Water Electrolysis

Hydrogen as an energy carrier is promising as it does not produce green-house gas (GHG) emissions at points of use and can be obtained from sources of low, or even neutral or negative GHG intensities [1,2]. One pathway to produce low emission hydrogen is water electrolysis when using a renewable power source [3]. However, freshwater, commonly used in this process, is relatively scarce, demand is high and expected to rise, and gets scarcer every day because of pollution [4,5,6]. An alternative is using saltwater, either through desalination or directly via adequate electrolysers [4]. Regarding direct use, a major challenge concerns catalyst, typically made of precious metals like Pt in the cathode, which are expensive, limited and susceptible to poisoning, e.g., by chlorine [7]. Likewise, in the anode chlorine is corrosive and reduces faradaic efficiency [4]. In this context, metal-coordinated nitrogen-carbon (M-N-C) nanostructures have proven to be attractive vis-à-vis these challenges [8]. To study their potential for saltwater electrolysis, five materials were synthesized following Malko et al. [8] using 1,5-diaminonaphthalene and 1% wt metallic sulphate salts of Co, Ni, Fe, Ni with Fe, and a blank without metal. The resulting material were suspended in 2-propanol and cast onto a vitreous carbon rotating ring disk electrode in both acidic solution 0,5M H2SO4 and saline medium 0,5M NaCl. Following electrode conditioning with cyclic voltammetries and electrochemical impedance characterization, linear sweep voltammetries (LSVs) were carried out in order to assess activity towards hydrogen evolution reaction (HER), coupled to hydrogen oxidation (HOR) at the Pt electrode in a ring-RDE (RRDE) fashion at constant potential of 0,3 V.The image presents HER and HOR plots in RRDE experiments at 1800 rpm, using either N-C or NiFe-N-C at a load of 0,27 mg cm-2 of catalyst at the disk and a Pt ring: (top) LSV at the disk (current normalized by geometric area, v = 2 mV/s), and (bottom) polarization at the Pt ring (E=0.3V vs NHE). Shown are both acidic medium (0.5 M H2SO4, N-C in 1 blue and NiFe-N-C in 2 red) and saline medium (0,5 M NaCl, N-C in 3 cyan and NiFe-N-C in 4 magenta). It was found that NiFe-N-C catalyst is active towards HER in saline medium at near neutral pH. As anticipated, the activity in acidic media is significantly higher than on saline medium, attributing this difference to several aspects such as conductivity limitations, chlorine presence and absence of free H+ ions and the need of additional steps for water dissociation [9]. In acidic media the metal-free catalyst (N-C) shows larger currents for most of the potential widow. On the other hand, the ring electrode does not show activity at all for N-C, thus it may be concluded that there is no H2 evolution and therefore the current is mostly capacitive, this capacitive contribution will be subtracted from the final results. In contrast, in saline medium N-C shows no activity at all towards HER, even showing smaller capacitive currents, while NiFe-C shows smaller albeit significant currents given the large differences in pH between media. The metal catalysts, the blank and a Pt/C in acidic and saline medium, will be compared using onset potentials, overpotentials at 10 mA/cm2 and Tafel slopes. References Blagojević , V. Minić, D. Minić D. & Grbović Novaković J. Hydrogen Economy: Modern Concepts, Challenges and Perspectives, Hydrogen Energy, IntechOpen (2012).Zhang,Y. & Zou, X. Noble metal-free hydrogen evolution catalysts for water splitting, Chemical Society Reviews, 15, (2015).IEA webstore, The Future of Hydrogen Seizing today´s opportunities, (2019).Dresp, S. Dionigi, F. Klingenhof, M. & Strasser, P. Direct Electrolytic Splitting of Seawater: Opportunities and Challenges, ACS Energy Letters (2019).Boretti, A. y Rosa L. Reassessing the projections of the World Water Development Report, npj Clean Water, 2, 15, (2019).Vos, J. & Koper, M. Measurement of competition between oxygen evolution and chlorine evolution using rotating ring-disk electrode voltammetry, Journal of Electroanalytical Chemistry, 819, (2018).Sethuraman, V. A. & .Weidner, J. W. Analysis of Sulfur Poisoning on a PEM Fuel Cell Electrode, Electrochimical acta, 55, 20, (2010).Malko, D. Lopes, T. Symianakis§a E. & Kucernak, A. The intriguing poison tolerance of non-precious metal oxygen reduction reaction (ORR) catalysts, Mater. Chem. A, 4, (2016).Zhou, Z. Pei, Z. Wei, L. Zhao, S. Jian, X. & Chen, Y. Electrocatalytic Hydrogen Evolution under Neutral pH Conditions: Current Understandings, Recent Advances, and Future Prospects, Energy Environ. Sci., 10, (2020) Figure 1