High Oxygen Reduction Reaction Research Articles

Highly Dispersed Mn-Doped Ceria Supported on N-Doped Carbon Nanotubes for Enhanced Oxygen Reduction Reaction.

The weak adsorption of oxygen on transition metal oxide catalysts limits the improvement of their electrocatalytic oxygen reduction reaction (ORR) performance. Herein, a dopamine-assisted method is developed to prepare Mn-doped ceria supported on nitrogen-doped carbon nanotubes (Mn-Ce-NCNTs). The morphology, dispersion of Mn-doped ceria, composition, and oxygen vacancies of the as-prepared catalysts were analyzed using various technologies. The results show that Mn-doped ceria was formed and highly dispersed on NCNTs, on which oxygen vacancies are abundant. The as-prepared Mn-Ce-NCNTs exhibit a high ORR performance, on which the average electron transfer number is 3.86 and the current density is 24.4% higher than that of commercial 20 wt % Pt/C. The peak power density of Mn-Ce-NCNTs is 68.1 mW cm-2 at the current density of 138.9 mA cm-2 for a Zn-air battery, which is close to that of 20 wt % Pt/C (69.4 mW cm-2 at 106.1 mA cm-2). Density functional theory (DFT) calculations show that the oxygen vacancy formation energies of Mn-doped CeO2(111) and pure CeO2(111) are -0.55 and 2.14 eV, respectively. Meanwhile, compared with undoped CeO2(111) (-0.02 eV), Mn-doped CeO2(111) easily adsorbs oxygen with the oxygen adsorption energy of only -0.68 eV. This work provides insights into the synergetic effect of Mn-doped ceria for facilitating oxygen adsorption and enhancing ORR performance.

ZIF-8 derived iron-, sulphur-, and nitrogen-doped catalysts for anion-exchange membrane fuel cell application

This study presents the preparation of tridoped Fe, N, S carbon-based catalysts using ZIF-8 as the main carbon source and iron(II)acetate, 1,10-phenanthroline, ammonia gas and thiourea as precursors for Fe, N and S elements. Thiourea was mixed via planetary ball-milling with a Fe–N–C catalyst prepared by inert gas pyrolysis, and different pyrolysis conditions were applied thereafter. The main goal of the work is to synthesise active non-precious metal electrocatalysts for oxygen reduction reaction (ORR). High electrocatalytic ORR activity in alkaline media was observed for the two materials obtained after thiourea addition and subsequent pyrolysis. Physico-chemical characterisation revealed successful S- and N-doping for all three catalysts with enhanced porosity for the two materials that were subjected to additional pyrolysis after the thiourea addition. The sulphur doping was highest for the FeNSC3 material that was subjected to a second pyrolysis in N2 and a third pyrolysis in NH3, compared to the FeNSC2 material that was subjected to a single pyrolysis in NH3 flow after thiourea addition. The ORR activity of FeNSC2 with half-wave potential of 0.88 V was slightly higher than that of FeNSC3, and the former was selected for evaluation as a cathode catalyst in an anion-exchange membrane fuel cell.

A highly oxygen reduction reaction active and CO2 durable high-entropy cathode for solid oxide fuel cells

One big obstacle for the oxygen reduction reaction (ORR) electrode in solid oxide fuel cells (SOFCs) is the poor reaction activity and fast degradations caused by CO2 poisoning. Here we report our design of an active A-site Ca-rich high-entropy Pr0.1875Ba0.1875Sr0.1875La0.1875Ca0.25CoO3-δ (PBSLC25C) electrode, guided by the O p-band theory. When applied as a cathode in solid oxide fuel cells (SOFCs), it demonstrates high ORR activity and excellent CO2 tolerance under realistic operating conditions. Ni-YSZ-based anode-supported cells with PBSLC25C cathodes demonstrate excellent peak power densities of 1.14 W cm−2, 1.04 W cm−2, and 0.77 W cm−2 in the air with 1%, 5%, and 10% CO2, respectively, at 750 °C. The engineered high-entropy PBSLC25C effectively diminishes the CO2 poisoning effect and maintains active surfaces for fast oxygen exchange, as confirmed by the cell durability test in air containing CO2 (5 and 10 vol%), Raman spectroscopy, and density functional theory calculations.

Well-dispersed Pt/Nb2O5 on zeolitic imidazolate framework derived nitrogen-doped carbon for efficient oxygen reduction reaction

In this work, an advanced hybrid material was constructed by incorporating niobium pentoxide (Nb2O5) nanocrystals with nitrogen-doped carbon (NC) derived from ZIF-8 dodecahedrons, serving as a support, referred to as Nb2O5/NC. Pt nanocrystals were dispersed onto Nb2O5/NC using a simple impregnation reduction method. The obtained Pt/Nb2O5/NC electrocatalyst showed high oxygen reduction reaction (ORR) activity due to three-phase mutual contacting structure with well-dispersed Pt and Nb2O5 NPs. In addition, the conductive NC benefits electron transfer, while the induced Nb2O5 can regulate the electronic structure of Pt element and anchor Pt nanocrystals, thereby enhancing the ORR activity and stability. The half-wave potential (E 1/2) for Pt/Nb2O5/NC is 0.886 V, which is higher than that of Pt/NC (E 1/2 = 0.826 V). The stability examinations demonstrated that Pt/Nb2O5/NC exhibited higher electrocatalytic durability than Pt/NC. Our work provides a new direction for synthesis and structural design of precious metal/oxides hybrid electrocatalysts.

Interlayer Polymerization to Construct a Fully Conjugated Covalent Organic Framework as a Metal-Free Oxygen Reduction Reaction Catalyst for Anion Exchange Membrane Fuel Cells.

Two-dimensional (2D) covalent organic frameworks (COFs) have a multilayer skeleton with a periodic π-conjugated molecular array, which can facilitate charge carrier transport within a COF layer. However, the lack of an effective charge carrier transmission pathway between 2D COF layers greatly limits their applications in electrocatalysis. Herein, by employing a side-chain polymerization strategy to form polythiophene along the nanochannels, a conjugated bridge is constructed between the COF layers. The as-synthesized fully conjugated COF (PTh-COF) exhibits high oxygen reduction reaction (ORR) activity with narrowed energy band gaps. Correspondingly, PTh-COF is tested as a metal-free cathode catalyst for anion exchange membrane fuel cells (AEMFCs) which showed a maximum power density of 176mWcm-2 under a current density of 533mAcm-2. The density functional theory (DFT) calculation reveals that interlayer conjugated polythiophene optimizes the electron cloud distribution, which therefore enhances the ORR performance. This work not only provides new insight into the construction of a fully conjugated covalent organic framework but also promotes the development of new metal-free ORR catalysts.

Novel electrocatalytic capacitive deionization with catalytic electrodes for selective phosphonate degradation: Performance and mechanism

Phosphonate is becoming a global interest and concern owing to its environment risk and potential value. Degradation of phosphonate into phosphate followed by the recovery is regarded as a promising strategy to control phosphonate pollution, relieve phosphorus crisis, and promote phosphorus cycle. Given these objectives, an anion-membrane-coated-electrode (A-MCE) doped with Fe-Co based carbon catalyst and cation-membrane-coated-electrode (C-MCE) doped with carbon-based catalyst were prepared as catalytic electrodes, and a novel electrocatalytic capacitive deionization (E-CDI) was developed. During charging process, phosphonate was enriched around A-MCE surface based on electrostatic attraction, ligand exchange, and hydrogen bond. Meanwhile, Fe2+ and Co2+ were self-oxidized into Fe3+ and Co3+, forming a complex with enriched phosphonate and enabling an intramolecular electron transfer process for phosphonate degradation. Additionally, benefiting from the stable dissolved oxygen and high oxygen reduction reaction activity of C-MCE, hydrogen peroxide accumulated in E-CDI (158 μM) and thus hydroxyl radicals (·OH) were generated by activation. E-CDI provided an ideal platform for the effective reaction between ·OH and phosphonate, avoiding the loss of ·OH and triggering selective degradation of most phosphonate. After charging for 70 min, approximately 89.9% of phosphonate was degraded into phosphate, and phosphate was subsequently adsorbed by A-MCE. Results also showed that phosphonate degradation was highly dependent on solution pH and voltage, and was insignificantly affected by electrolyte concentration. Compared to traditional advanced oxidation processes, E-CDI exhibited a higher degradation efficiency, lower cost, and less sensitive to co-existed ions in treating simulated wastewaters. Self-enhanced and selective degradation of phosphonate, and in-situ phosphate adsorption were simultaneously achieved for the first time by a E-CDI system, showing high promise in treating organic-containing saline wastewaters.

Bifunctional oxygen electrocatalyst based on Fe, Co, and nitrogen co-doped graphene-coated alumina nanofibers for Zn-air battery air electrode

Aqueous rechargeable zinc-air battery (RZAB) is an emerging environmentally friendly energy storage device for a wide variety of industrial applications such as electric vehicles, consumer electronics, and stationary power plants. For successful commercialization of RZABs, a cost-effective bifunctional catalyst is highly required to catalyze the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the air electrode. Dual transition-metal and nitrogen-doped nanocarbon materials have shown good potential as an affordable and scalable bifunctional oxygen electrocatalysts alternative to Pt-group metal-based catalysts for RZAB. To achieve this goal, we have developed electrocatalysts based on Fe, Co, and nitrogen co-doped graphene-augmented inorganic alumina nanofibers (Fe/Co-NGr). The Fe/Co-NGr catalysts demonstrate high oxygen reduction and evolution reaction reversibility (ΔE) of 0.85–0.88 V due to the graphene-covered nanofibrous structure doped with FeCo alloy nanoparticles and containing nitrogen, transition metal (TM) coordinated to nitrogen and TM oxide active sites. The primary zinc-air battery with Fe/Co-NGr air electrode exhibits a high maximum power density of 149 mW cm−2 and a specific capacity of 807 mAh gZn-1. The RZAB assessment has shown a low charge–discharge voltage gap of 0.86 V and high energy utilization efficiency of 58 % up to 90 h of charge–discharge cycling at 5 mA cm−2.

Ultrathin Ni–N–C layer modified Pt–Ni alloy nanoparticle catalysts for enhanced oxygen reduction

Accelerating the commercialization of fuel cells requires the development of Pt-based alloy cathode catalysts with high ORR operation, low price, and excellent reliability. However, it is a challenging task to fabricate uniformly dispersed, low-loaded, and small-sized Pt-based alloy catalysts to resolve the contradiction between activity and stability. Here, sub-3 nm N-doped PtNi nanoparticles (NPs) are synthesized as high-performance PEMFC cathode catalysts. PtNi/Ni-NC exhibits excellent electrocatalytic activity (0.51 A mgPt−1@0.8 V and peak power density of 328 mW cm−2) as well as stability (only 15 mV loss in E1/2 after 5000 cycles of ADT tests) in oxygen reduction reaction (ORR). The experimental results show that N doping modulates the electronic structure around Pt and optimizes the lattice compressive strain, thus attenuating the adsorption of oxygen intermediates on the surface Pt and enhancing the ORR activity. Meanwhile, the encapsulation of PtNi NPs by the constructed ultrathin Ni–N–C layer accounts for the improved stability. This work offers a novel perspective f for raising the stability and catalytic performance of Pt-based catalysts.

Unraveling the Activity and Mechanism of TM@g-C4N3 Electrocatalysts in the Oxygen Reduction Reaction.

In this work, a high-throughput screening strategy and density functional theory (DFT) are jointly employed to identify high-performance TM@g-C4N3 (TM = 3d, 4d, 5d transition metals) single-atom catalysts (SACs) for the oxygen reduction reaction (ORR). Comprehensive studies demonstrated that Cu@, Zn@, and Ag@g-C4N3 show high ORR catalytic activities under both acidic and alkaline conditions with favorable overpotentials (ηORR) of 0.70, 0.89, and 0.89 V, respectively; among them, Cu@g-C4N3 is the best candidate. The ORR follows a four-electron mechanism with the final product H2O/OH-. Cu@, Zn@, and Ag@g-C4N3 catalysts also exhibit good thermal (500 K) and electrochemical (0.93-3.14 V) stabilities. Cu@, Zn@, and Ag@g-C4N3 demonstrate superior activities with low ηORR due to its moderate adsorption strength of *OH. The ηORR and the Gibbs free energy changes of *OH (ΔG4(acidic)/ΔG4(alkaline)) resemble a volcano-type relationship under acidic/alkaline conditions, respectively. Additionally, the O-O bond length in *OOH emerged as an effective structural descriptor for rapidly identifying the promising electrocatalysts. This research provides valuable insights into the origin of the ORR activity on TM@g-C4N3 and offers useful guidance for the efficient exploration of high-performance catalyst candidates.

Regulating the Electronic Synergy of Asymmetric Atomic Fe Sites with Adjacent Defects for Boosting Activity and Durability toward Oxygen Reduction

AbstractThe oxygen reduction reaction (ORR) plays a fundamental role in sustainable energy technologies. However, the creation of non‐precious metal electrocatalysts with high ORR activity and durability under all pH conditions is of great significance but remains challenging. Herein, the aim is to overcome this challenge by creating a Fe single atom catalyst on a 2D defect‐containing nitrogen‐doped carbon support (Fe1/DNC) via a microenvironment engineering strategy. Microkinetic modeling reveals that FeN4(OH) moieties are the real active sites under reaction conditions. Due to the synergistic promotion effect of denser accessible FeN4(OH) moieties and defect‐induced electronic properties, Fe1/DNC catalyst achieves extraordinary ORR activity under alkaline, acidic, and neutral conditions, with half‐wave potentials of 0.95, 0.82, and 0.70 V, respectively. Moreover, a negligible performance decay is observed with this Fe catalyst in stability and methanol tolerance tests. Zn‐air battery employing Fe1/DNC delivers remarkable peak power density and long‐term operational durability. Theoretical analysis provides compelling evidence that the defects adjacent to FeN4(OH) moieties can endow an inductive effect to reshape electronic properties to balance the OOH* formation and OH* reduction. This work offers insight into the regulation of asymmetric coordination structure and electronic properties of metal sites for boosting electrocatalytic activity and stability.

High entropy La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 with tailored eg occupancy and transition metal-oxygen bond properties for oxygen reduction reaction

Forming high entropy oxide provides a feasible approach to finding a balance among moderate eg occupancy, high transition metal-oxygen (TM-O) covalency, and lattice energy, which is essential to ensure efficient and durable oxygen reduction reaction (ORR) process for perovskite lanthanide-transition metal oxides (LaTMO3). However, due to the compositional complexity, clarifying the relevance among the high entropy components, eg occupancy, TM-O properties, and ORR performance still remains a challenge. Herein, adopting the B site entropy-driven strategy, a series of LaTMO3 (TM = Cr, Mn, Fe, Co, Ni) with tunable eg occupancy and TM-O bond properties are synthesized, and the correlations between high entropy elements, eg occupancy, TM-O properties, and ORR performances are revealed quantitively based on the crystal field theory and the Phillips–Van Vechten–Levine (P–V–L) valence bond theory. High entropy La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 delivers a low overpotential of 493 mV (vs. 503 mV for LaMnO3) and a minuscule decline by only 1.7% (vs. 4.4% for LaMnO3) in half wave potential after 10,000 cycles, which can be associated with the tailored eg occupancy (1.06) and the significant enhancement in both TM-O covalency (4%) and lattice energy (691.75 kJ mol–1). This work not only demonstrates the prospects of high entropy LaTMO3 in the ORR field but also provides a new perspective for the quantitative analysis of the structure-activity relationship for high entropy oxide ORR catalysts.

Fe[sbnd]N doped carbon materials from oily sludge as electrocatalysts for alkaline oxygen reduction reaction

Alkaline oxygen reduction reaction (ORR) presents an important role for energy conversion technologies and requires the development of an efficient electrocatalyst. Pt-based catalysts provide suitable activity; however, Pt production accessibility and high costs create hurdles to their commercial implementation. Fe coordinated within N-doped carbon materials (FeNC) are a promising alternative due to their high ORR catalytic activity, although the currently commercially available FeNC materials rely on harsh synthetic protocols which can lead to increased environmental impacts. In this work we target this issue by taking advantage of an oily sludge waste currently generated in refineries to synthesize FeNC materials, thus, avoiding the environmental impact caused by the management of this waste. The solid particles within oily sludge, which present a high concentration of C and Fe, were combined by different nitrogen sources and pyrolyzed at high temperatures.The prepared materials present a hierarchical pore structure with surface areas up to 547 m2 g−1. X-ray photoelectron spectroscopy analysis found that the impregnation of N using phenanthroline promotes the formation of pyridinic-N structures, which enhances the ORR performance compared to melamine doping. Additional doping of Fe with phenanthroline results in an ORR mass activity of 1.23 ± 0.04 A gFeNC−1 at 0.9 VRHE, iR-free in a rotating disc electrode (0.1 M KOH). This catalyst also shows a lower relative loss in activity at 0.9 VRHE after 8000 cycles in O2-saturated conditions compared to a commercial FeNC catalyst, PMF D14401, (−63.5 vs −69 %, respectively), demonstrating promise as a cheap and simple route to FeNC catalysts for alkaline ORR.

Self-powered Pb(II) removal driven by Zn-air batteries using N, P-doped active straw carbon as cathode

Electrochemical systems have been widely applied in heavy-metal ions (HMIs) pollution control, while their applications are greatly restricted by excessive energy consumption. Self-powered environmental remediation systems (SERSs) can shed the energy reliance to achieve HMIs decontamination and simultaneous electricity output through electrokinetic migration. In this work, SERSs based on Zn-air batteries (ZABs) were achieved to remove bivalent lead (Pb(II)) by circulating effluent as electrolyte. Straw biomass derived N, P functional active nanocarbon (NP-ASC) with hierarchical porosity and electron modulation effect was designed for achieving high oxygen reduction reaction (ORR) activity and efficient Pb(II) uptake. SERSs with electrode active area of 1 cm2 realize outstanding Pb(II) removal efficiency (98.1 %) and electricity generation (67.5 mWh∙cm−2) in simulated sewage. ZABs assembled with NP-ASC delivered specific capacity of 795 mAh∙g−1 and cycling stability for 340 h. This study provides a guide for designing a novel SERS using functionalized biomass nanocarbon.

TiN as Radical Scavenger in Fe─N─C Aerogel Oxygen Reduction Catalyst for Durable Fuel Cell.

Fe─N─C is the most promising alternative to platinum-based catalysts to lower the cost of proton-exchange-membrane fuel cell (PEMFC). However, the deficient durability of Fe─N─C has hindered their application. Herein, a TiN-doped Fe─N─C (Fe─N─C/TiN) is elaborately synthesized via the sol-gel method for the oxygen-reduction reaction (ORR) in PEMFC. The interpenetrating network composed by Fe─N─C and TiN can simultaneously eliminate the free radical intermediates while maintaining the high ORR activity. As a result, the H2 O2 yields of Fe─N─C/TiN are suppressed below 4%, ≈4 times lower than the Fe─N─C, and the half-wave potential only lost 15mV after 30 kilo-cycle accelerated durability test (ADT). In a H2 ─O2 fuel cell assembled with Fe─N─C/TiN, it presents 980mAcm-2 current density at 0.6V, 880mWcm-2 peak power density, and only 17mV voltage loss at 0.80Acm-2 after 10 kilo-cycle ADT. The experiment and calculation results prove that the TiN has a strong adsorption interaction for the free radical intermediates (such as *OH, *OOH, etc.), and the radicals are scavenged subsequently. The rational integration of Fe single-atom, TiN radical scavenger, and highly porous network adequately utilize the intrinsic advantages of composite structure, enabling a durable and active Pt-metal-free catalyst for PEMFC.

Application of vertically ordered polyaniline nanofibers in enhancing the ORR activity of Pt catalysis

Pt-based nanocatalysts supported on carbon materials have exhibited remarkable catalytic activity in the oxygen reduction reaction (ORR). However, these catalysts still encounter challenges such as low utilization efficiency, weak binding strength with substrate and proneness to detachment from it. Consequently, we explore the potential application of electron-rich polymer as carrier in high efficiency ORR catalysts, the uniformly distributed Pt-PANI catalyst is successfully synthesized by taking advantage of ion-exchange property of polyaniline (PANI). As an emerging catalyst for ORR, Pt-PANI shows excellent ORR performance in acidic solution, the vertically aligned PANI nanoarrays accelerate the ion diffusion in electrolyte and promote the charge transfer at the interface, improving the catalytic activity of low-loading Pt-based catalyst. In short, this work provides a novel alternative beyond conventional carbonaceous materials for the selection of carriers for Pt-based catalyst.

General Pyrolysis for High-Loading Transition Metal Single Atoms on 2D-Nitro-Oxygeneous Carbon as Efficient ORR Electrocatalysts.

Single-atom catalysts (SACs) possess the potential to involve the merits of both homogeneous and heterogeneous catalysts altogether and thus have gained considerable attention. However, the large-scale synthesis of SACs with rich isolate-metal sites by simple and low-cost strategies has remained challenging. In this work, we report a facile one-step pyrolysis that automatically produces SACs with high metal loading (5.2-15.9 wt %) supported on two-dimensional nitro-oxygenated carbon (M1-2D-NOC) without using any solvents and sacrificial templates. The method is also generic to various transition metals and can be scaled up to several grams based on the capacity of the containers and furnaces. The high density of active sites with N/O coordination geometry endows them with impressive catalytic activities and stability, as demonstrated in the oxygen reduction reaction (ORR). For example, Fe1-2D-NOC exhibits an onset potential of 0.985 V vs RHE, a half-wave potential of 0.826 V, and a Tafel slope of -40.860 mV/dec. Combining the theoretical and experimental studies, the high ORR activity could be attributed its unique FeO-N3O structure, which facilitates effective charge transfer between the surface and the intermediates along the reaction, and uniform dispersion of this active site on thin 2D nanocarbon supports that maximize the exposure to the reactants.

Trifunctional robust electrocatalysts based on 3D Fe/N‐doped carbon nanocubes encapsulating Co4N nanoparticles for efficient battery‐powered water electrolyzers

AbstractHerein, we have designed a highly active and robust trifunctional electrocatalyst derived from Prussian blue analogs, where Co4N nanoparticles are encapsulated by Fe embedded in N‐doped carbon nanocubes to synthesize hierarchically structured Co4N@Fe/N–C for rechargeable zinc–air batteries and overall water‐splitting electrolyzers. As confirmed by theoretical and experimental results, the high intrinsic oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction activities of Co4N@Fe/N–C were attributed to the formation of the heterointerface and the modulated local electronic structure. Moreover, Co4N@Fe/N–C induced improvement in these trifunctional electrocatalytic activities owing to the hierarchical hollow nanocube structure, uniform distribution of Co4N, and conductive encapsulation by Fe/N–C. Thus, the rechargeable zinc–air battery with Co4N@Fe/N–C delivers a high specific capacity of 789.9 mAh g−1 and stable voltage profiles over 500 cycles. Furthermore, the overall water electrolyzer with Co4N@Fe/N–C achieved better durability and rate performance than that with the Pt/C and IrO2 catalysts, delivering a high Faradaic efficiency of 96.4%. Along with the great potential of the integrated water electrolyzer powered by a zinc–air battery for practical applications, therefore, the mechanistic understanding and active site identification provide valuable insights into the rational design of advanced multifunctional electrocatalysts for energy storage and conversion.

Efficient preparation of carbon materials composed of warped graphene layers via in-situ nano-templating and estimation of oxygen reduction reaction activity

The warped graphene layer (WGL) has garnered attention as a potential alternative to Pt for oxygen reduction reaction (ORR) catalysts and as a platform for enhancing the activity of Pt or molecular catalysts through interactions. We propose an in-situ nano-templating method for the preparation and mass production of WGLs and demonstrate its efficiency. The in-situ nano-templating method facilitates the synthesis of materials with three-dimensional curvature by concurrently generating nanoparticles and carbonizing. The synthesized WGLs exhibited high ORR activity in acidic conditions. Although the ORR activity was not correlated with the surface area, it was strongly correlated with the curvature radius of the WGLs. This activity was considered to arise owing to the optimization of oxygen adsorption ΔG0 with the decrease in the curvature radius of the WGLs; furthermore, the physicochemical characteristics of WGL possesses continuity of carbon layers and exhibit a Fermi level higher than the O2/H2O reduction potential. This report elucidates experimentally that WGLs contribute to ORR activity, suggesting the importance of incorporating WGLs in the development of non-precious metal catalysts.

Electrocatalytic degradation of Favipiravir by heteroatom (P and S) doped biomass-derived carbon with high oxygen reduction reaction activity

In this study, a biomass-derived carbon block with heteroatoms (P and S) self-doped graphene structure was successfully synthesized by spent coffee grounds (SCG) directly sintered method. The spent coffee grounds biomass-derived carbon (SCC) block was used as electrocatalytic electrode to effectively degrade the antiviral drug of Favipiravir (FAV) in water, which represented excellent oxygen reduction reaction (ORR) activity with the H2O2 production. The doped heteroatoms in the graphene structure of SCC provided many active sites in the electrocatalytic electrode for ORR as well as more production of reactive OH･. Based on the structural characterization, radical species identification and intermediate products analysis, the reaction mechanism of FAV degradation by the SCC block electrode was proposed. This catalytic system also showed high ecological safety that the ecological toxicity for Vibrio fischeri was significantly reduced with the degradation process of FAV. The degradation of FAV in recycle test and in real sample of lake water, well water, tap water all demonstrated high stability of structure and catalytic activity of SCC. The electrocatalytic system based on SCC block electrode has realized the recycling and utilization of biomass resources and has promising application on the removal of environmental pollutants.

N‐Decorated Main‐Group MgAl2O4 Spinel: Unlocking Exceptional Oxygen Reduction Activity for Zn‐Air Batteries

AbstractThe development of economical and efficient oxygen reduction reaction (ORR) catalysts is crucial to accelerate the widespread application rhythm of aqueous rechargeable zinc‐air batteries (ZABs). Here, a strategy is reported that the modification of the binding energy for reaction intermediates by the axial N‐group converts the inactive spinel MgAl2O4 into the active motif of MgAl2O4‐N. It is found that the introduction of N species can effectively optimize the electronic configuration of MgAl2O4, thereby significantly reducing the adsorption strength of *OH and boosting the reaction process. This main‐group MgAl2O4‐N catalyst exhibits a high ORR activity in a broad pH range from acidic and alkaline environments. The aqueous ZABs assembled with MgAl2O4‐N shows a peak power density of 158.5 mW cm−2, the long‐term cyclability over 2000 h and the high stability in the temperature range from ‐10 to 50 °C, outperforming the commercial Pt/C in terms of activity and stability. This work not only serves as a significant candidate for the robust ORR electrocatalysts of aqueous ZABs, but also paves a new route for the effective reutilization of waste Mg alloys.