non-Pt Electrocatalysts Research Articles

Modulating dual-active sites within one ruthenium nanocluster by engineering electronic metal-support interactions for efficient hydrogen electro-oxidation

Designing non-Pt metal electrocatalysts for alkaline hydrogen oxidation reaction (HOR) is highly desirable to address the unsustainable use of high-cost and scarce Pt. Although challenging, this study introduces an ultrasmall Ruthenium nanoclusters (Ru NCs)-based electrocatalyst with dual active sites for efficient alkaline HOR. While the selection of Ru is based on its cost-effectiveness, smaller atomic number, and comparable physicochemical properties to Pt, the employment of Mo2C as the support is mainly for establishing strong electronic metal-support interaction (EMSI) within the catalyst. This EMSI effect facilitates significant charge redistribution and the formation of efficient dual-active sites within a single Ru NC. Experiments and simulations confirm that the EMSI effect modulates the d-band centers of the Ru NCs at both H-adsorption and OH-adsorption sites, endowing the Ru/Mo2C catalyst with up to 16.6 times and 29.7 times higher mass activity than commercial Pt/C and Ru/C, respectively, as well as enhanced long-term stability and CO resistance. This work provides a paradigm in designing non-Pt metal NCs for alkaline HOR electrocatalysis, underscoring the significance of adjusting the EMSI effect for performance escalation of HOR catalysis.

N-doped carbon-enveloped CoSe2/NiSe2@Cu2Se core-shell nanospheres as non-Pt electrocatalysts for enhanced wide-pH hydrogen evolution reactions

An available approach to ameliorate the property of electrocatalysts for transition metal selenides (TMSs) is to transform their structure, morphology, and elemental composition, especially for hydrogen evolution reactions (HER), which can be a long-term task. In this work, Ni-Co nanospheres were synthesized by a hydrothermal method, and then in the synchronous processes of selenization and carbonization, it reacted with the peripherally coated melamine-copper complex, which was the reactant between melamine and copper ions. Ultimately, CoSe2/NiSe2@Cu2Se-NC nanospheres with a core-shell structure were synthesized after annealing process. This special structure provided more active attachment sites, enabling CoSe2/NiSe2@Cu2Se-NC to exhibit excellent HER properties under wide-pH range. Especially, in acidic conditions, it had a low initial potential of 41.0 mV, a small Tafel slope value of 48.7 mV dec–1, and a long service life. The proposed scheme indicates that a new approach will be added to the synthesis of electrocatalysts based on TMSs.

Healing the structural defects of spinel MnFe2O4 to enhance the electrocatalytic activity for oxygen reduction reaction

Spinel metal oxides containing Mn, Co, or Fe (AB2O4, A/B = Mn/Fe/Co) are one of the most promising non-Pt electrocatalysts for oxygen reduction reaction (ORR) in alkaline conditions. However, the low conductivity of metal oxides and the poor intrinsic activities of transition metal sites lead to unsatisfactory ORR performance. In this study, eutectic molten salt (EMS) treatment is employed to reconstruct the atomic arrangement of MnFe2O4 electrocatalyst as a prototype for enhancing ORR performance. Comprehensive analyses by using XAFS, soft XAS, XPS, and electrochemical methods reveal that the EMS treatment reduces the oxygen vacancies and spinel inverse in MnFe2O4 effectively, which improves the electric conductivity and increases the population of more catalytically active Mn2+ sites with tetrahedral coordination. Moreover, the enhanced Mn-O interaction after EMS treatment is conducive to the adsorption and activation of O2, which promotes the first electron transfer step (generally considered as the rate-determining step) of the ORR process. As a result, the EMS treated MnFe2O4 catalyst delivers a positive shift of 40 mV in the ORR half-wave potential and a two-fold enhanced mass/specific activity. This work provides a convenient approach to manipulate the atomic architecture and local electronic structure of spinel oxides as ORR electrocatalysts and a comprehensive understanding of the structure-performance relationship from the molecular/atomic scale.

Crystalline-Amorphous Heterophase PdMoCrW Tetrametallene: Highly Efficient Oxygen Reduction Electrocatalysts for a Long-Term Zn-Air Battery.

Metallenes have received sustained attention owing to their unique microstructure characteristics and compelling catalytic applications, but the synthesis of multielement crystalline-amorphous metallenes remains a formidable challenge. Herein, we report a one-step wet chemical reduction method to synthesize composition-tunable crystalline-amorphous heterophase PdMoCrW tetrametallene. As-synthesized PdMoCrW tetrametallene is composed of approximately six to seven atomic layers and has flexible crimpiness, a crystalline-amorphous heterophase structure, and high-valence metal species. Time-dependent experiments show that PdMoCrW tetrametallene follows a three-step growth mechanism that includes nucleation, lateral growth, and atom diffusion, respectively. The novel ultrathin structure, optimized Pd electronic structure, and hydrophilic surface together greatly promote the activity and stability of PdMoCrW tetrametallene in the alkaline oxygen reduction reaction. Pd75.9Mo9.4Cr8.9W5.8/C exhibits excellent mass and specific activities of 2.81 A mgPd-1 and 4.05 mA cm-2, which are 20.07/14.46 and 23.42/16.20 times higher than those of commercial Pt/C and Pd/C, respectively. Furthermore, a Zn-air battery assembled using Pd75.9Mo9.4Cr8.9W5.8/C as a cathode catalyst achieves a peak power density of 156 mW cm-2 and an ultralong durability of 329 h. This study reports an effective strategy for constructing crystalline-amorphous quaternary metallenes to advance non-Pt electrocatalysts toward oxygen reduction reaction (ORR) performance and for a Zn-air battery.

Tuning the morphology and crystal phase of Ru nanocatalysts for efficient hydrogen evolution

Regulation of crystal phase of Ru nanocatalysts has been identified as an effective approach in regulating the bonding strength of reaction intermediates to Ru and improving the intrinsic activity of Ru-based catalysts during electrocatalytic hydrogen evolution reaction (HER). Here, we reported that the morphology and crystal phase of Ru nanocatalysts could be facilely regulated by halide anions in hydrothermal synthesis. Structural characterization revealed that halogen anions directed the anisotropic growth of hcp Ru, stabilized Ru crystals from aggregation, and increased the abundance of grain boundaries. As a result, The Ru polycrystalline networks exhibited excellent HER activity and durability with a smaller Tafel slope of 21 mV dec−1 and overpotential (η50) of 18 mV. This work sheds light on the shape and phase control of nanocrystals and future design of high-efficient non-Pt electrocatalysts with enhanced HER performance.

Pd@CoFe Alloys on N-Doped Carbon Derived from Charred Tissue Paper as Synergistic Bifunctional Oxygen Electrocatalysts

Integrating more active components into a catalyst material could facilitate the development of multifunctional electrocatalysts for energy conversion and storage applications. In this study, we developed a multifunctional electrocatalyst, namely, Pd alloyed with Co-Fe deposited on N-doped mesoporous carbon derived from tissue paper (Pd@Co-Fe/N-TDC). The synergism in Pd@Co-Fe/N-TDC, stemming from the interatomic alloy between Pd and Co-Fe, N-doped mesoporous carbon with defective surfaces, distribution of polyhedral Pd nanoparticles, and strong metal-support interfacial interaction, resulted in significantly high electrocatalytic performance for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Pd@Co-Fe/N-TDC was found to be an efficient bifunctional oxygen electrocatalyst, and this was evidenced by a high onset potential (1.01 V) and kinetic current density (2.6 mA/cm2) for the ORR and by a low overpotential (296 mV) and a low Tafel slope value (38 mV/dec) for the OER, along with a small ΔE of 736 mV. The catalyst also exhibited high durability for both ORR and OER, even after 10000 and 5000 cycles, respectively. Theoretical assessment provides an insight into the synergism of active metal sites in Pd@Co-Fe/N-TDC, which showed its potential for use as a non-Pt electrocatalyst for energy applications.

A unique sandwich-structured Ru-TiO/TiO2@NC as an efficient bi-functional catalyst for hydrogen oxidation and hydrogen evolution reactions

Developing active and stable non-Pt electrocatalysts for hydrogen oxidation (HOR) and evolution reactions (HER) are critical for anion exchange membrane fuel cells and water electrolyzers. Herein, we report a highly active and robust electrocatalyst Ru-TiO/TiO2@NC, in which Ru nanoclusters are sandwiched between TiO/TiO2 nanosheets and nitrogen-doped carbon layers. Taking advantage of both the optimized Ru-TiO/TiO2 interaction and the conductive carbon coating layers, the Ru-TiO/TiO2@NC exhibits both exceptional HOR/HER activity and superior stability, outperforming Pt/C in the alkaline solution. The HOR mass activity reaches up to 107.2 A gRu-1 at an overpotential of 50 mV, and the specific exchange current density is 0.271 mA cm−2. The HER overpotential at 10 mA cm−2 is only 39 mV, 34 mV lower than required by Pt/C. More importantly, the Ru-based catalyst exhibits excellent anti-oxidation ability by virtue of the unique sandwich structure. Density functional theory calculations discover that the d-band center of Ru in Ru-TiO/TiO2 is downshifted by 0.29 eV compared to Ru-TiO2, decoupling and optimizing the Had/OHad adsorption on Ru, i.e., Had is promoted, while OHad is inhibited and transferred to TiO/TiO2. As a result, (i) the energy required by the potential determining step of HOR/HER is lowered, and (ii) the anti-oxidation ability of the Ru-TiO/TiO2 is enhanced. This work not only addresses the issue of Ru passivation at high anode potentials but also provides an innovative and versatile approach to designing advanced electrocatalysts.

Nickel-doped molybdenum diselenide/functionalized multiwalled carbon nanotube as highly efficient non-Pt electrocatalyst toward methanol oxidation reaction

Designing a highly active, cost-effective, poison-resistant, and durable noble-metal-free electrocatalyst is essential for improvement of direct methanol fuel cells performance. In this work, Ni-doped MoSe2 nanosheets were successfully synthesized and integrated with carboxylated multiwalled carbon nanotube (f-MWCNT). The formation of Ni-doped MoSe2/f-MWCNT was confirmed with field emission scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy techniques. The prepared nanocomposite was used as an electrochemical catalyst for methanol electro-oxidation. The Ni-doped MoSe2/f-MWCNT electrocatalyst displayed a low onset potential of 0.33 V and methanol oxidation reaction (MOR) activity of 630 mA/cm2 at 0.8 V vs. Ag/AgCl after addition of 1 M methanol in alkaline solution. The proposed electrocatalyst also presented outstanding stability with 90% of its MOR activity retention even after 8000 s. With its facile synthesis, excellent catalytic performance and high stability, Ni-doped MoSe2/f-MWCNT is promising as an inexpensive, CO-resistant and efficient anode catalyst for MOR.

Porous Fe, N co-doped carbon with high electrocatalytic oxygen reduction reaction performance in Zn-air battery

Non-Pt electrocatalysts for oxygen reduction reactions (ORR) have been developed using metal and nitrogen co-doped carbon electrocatalysts. However, challenges remain regarding the porosity of the catalyst, distribution of active sites, and the easy aggregation of the metal components. Herein, we report a bottom-up preparation strategy to obtain a porous ethynyl-linked conjugated microporous polymer (CMP) precursor containing triazine units and bipyridine, ensuring high N content and coordination with Fe 3+ . The Fe doped CMP is then carbonization into a Fe, N co-doped nanoporous carbon material (BPCMP-Fe-800), which can be taken as the electrocatalyst in ORR. BPCMP-Fe-800 catalyst exhibits electrocatalytic performance dominated by 4e − transfer mechanism with the onset potential of 0.97 V, half-wave potential of 0.85 V, and higher kinetic current density of 11.3 mA cm −2 (0.8 V). In addition, when applied as cathode electrocatalyst in zinc-air batteries, BPCMP-Fe-800 displays more competitive power density (179.5 mW cm −2 ) and specific capacity (790.5 mAh g −1 ) compared with Pt/C. Our study demonstrates a general and facile approach for porous Fe, N co-doped carbon with the potential as alternatives to Pt catalysts for efficient ORR catalytic performances and provides new insights of multi-atom catalysts for other energy conversion related catalytic reactions.

Highly Efficient Methanol Oxidation Reaction Achieved by Cobalt Doping in Delafossite AgNi1–xCoxO2 Solid Solution

Developing highly active and durable non-platinum catalysts for methanol oxidation is of great significance for direct methanol fuel cells. However, their electrocatalytic efficiency is still insufficient mainly due to their poor electrical conductivity and slow reaction kinetics. Herein, a non-Pt electrocatalyst AgNi0.8Co0.2O2 with a delafossite structure is facilely constructed via a cation-exchange strategy for the methanol oxidation reaction in alkaline media. The introduction of Co atoms is favorable to crystallization for boosting the synthesis procedure. Meanwhile, the uniform distribution of Co and Ni in the structure brings about additional oxygen vacancies in the materials, thereby improving the intrinsic methanol oxidation reaction activity of the catalysts, and the introduced Co atoms can help to oxidize intermediates such as formaldehyde. Therefore, the electrocatalyst exhibits excellent electrocatalytic performance (77.6 mA cm–2, 220 mA mg–1) and high selectivity, and it can effectively inhibit the oxygen evolution reaction (310 mV difference from the oxygen evolution reaction potential at 10 mA cm–2). This work not only provides a material system using cheap and effective non-Pt catalysts based on Ag-based delafossite oxides but also sheds light on the engineering of oxygen vacancies of electrocatalysts for developing high-performance direct methanol fuel cells.

Building 3D Interconnected MoS2 Nanosheet–Graphene Networks Decorated with Rh Nanoparticles for Boosted Methanol Oxidation Reaction

The development of direct methanol fuel cell technology is one of the important ways to establish green energy production and conversion systems, while its large-scale commercial applications are severely hindered by the high cost and insufficient performance of current Pt-based anode catalysts. Here, we report the design and construction of a novel non-Pt electrocatalyst made from three-dimensional (3D) interconnected MoS2 nanosheet–reduced graphene oxide networks decorated with ultrafine Rh nanoparticles (Rh/MoS2-RGO) via a controllable co-assembly strategy. With unique structural features such as large specific surface areas, 3D interweaving porous frameworks, uniform Rh distribution, and excellent electron conductivity, the optimized Rh/MoS2-RGO catalyst is endowed with boosted electrocatalytic methanol oxidation properties, including a large electrochemical active surface area of 95.5 m2 g–1, a high mass (specific) activity of 1502.0 mA mg–1 (1.57 mA cm–2), and robust long-term stability, all of which significantly outperform those of reference Rh/RGO, Rh/carbon black, Rh/MoS2, as well as commercial Pt/carbon black and Pd/carbon black catalysts with the same metal content.

Ru nanoparticles decorated Ni-V2NO heterostructures in carbon nanofibers as efficient electrocatalysts for hydrogen evolution reaction

• Integration of Ru nanoparticles and Ni-V 2 NO heterostructures via electrospinning. • Electronic donation of Ni-V 2 NO to tune the electronic structure of Ru. • The introduction of Ni-V 2 NO can generate numerous accessible active sites. • Noticeably enhanced HER activity caused by the interaction between Ru and Ni-V 2 NO. Herein, we have successfully synthesized a non-Pt electrocatalyst in form of Ru nanoparticles decorated Ni-V 2 NO heterostructures in carbon nanofibers (Ru/Ni-V 2 NO/NCNFs) through annealing electrospun produced Ru-Ni 3 V 2 O 8 -PAN nanofibers under Ar atmosphere. The integration of Ru nanoparticles and Ni-V 2 NO heterostructures can regulate the electronic structure of Ru by the interaction among active components and thereby benefit the improvement of HER performance. Meanwhile, enormously boosted ECSA can be detected as the introduction of Ni-V 2 NO heterostructures, which reveals the favorable exposure of active sites. Thus, compared to the samples solo modified by Ru or Ni-V 2 NO, the as-fabricated Ru/Ni-V 2 NO/NCNFs has shown distinctly improved HER performance delivering an overpotential of merely 74.5 mV at 10 mA cm −2 with Tafel slope of 60.7 mV/dec and long-term stability in alkaline solution. It is believed that our work can provide reasonable inspirations for the design of novel non-Pt heterostructured electrocatalysts used in hydrogen generation via electrochemical water splitting.

L-Lysine derived fabrication of Cu@Ni core–satellite nanoassemblies as efficient non-Pt catalysts for the methanol oxidation reaction

With assistance of l-lysine, Cu@Ni core–satellite nanoassemblies were fabricated, which could serve as efficient non-Pt electrocatalysts for the methanol oxidation reaction due to both the component effects and structural features.

(Invited) A Perspective on Scientific Issues and Requirements for Ultra-Low Platinum Proton Exchange Membrane Fuel Cells

The fuel of hydrogen has remarkable characteristics including renewable, zero emission and high power density, thus making it hotly pursued for the new round of world energy technology revolution. Hydrogen fuel cells are considered the ultimate solution for future clean energy vehicles. However, limited by global reserves and exploitation, the high cost caused by applying noble metal (Pt) in membrane electrode assemblies (MEAs) has become a "bottleneck" for the large-scale promotion of fuel cell vehicles. A continuous reduction in Pt loading will hardly satisfy the requirements of high power output, long life, adaption to extreme operating conditions in various application fields of fuel cells1-3. Herein, the scientific issues concerning both kinetics and mass transfer in ultra-low Pt MEAs are first revealed. Then, the development of highly efficient Pt or non-Pt electrocatalysts for oxygen reduction are introduced. Finally, some innovative solutions dealing with MEAs and flow field are provided. It is believed that this should provide both scientific and technical supports for the development of ultra-low Pt proton exchange membrane fuel cells. Keywords: ultra-low Platinum, membrane electrode assemblies, kinetics and mass transfer, highly efficient Pt or non-Pt electrocatalysts, oxygen reduction reaction, proton exchange membrane fuel cells Reference [1] C. Wang, X.J. Cheng, J.B. Lu, S.Y. Shen, X.H. Yan, J.W. Yin, G.H. Wei and J.L. Zhang, The Journal of Physical Chemistry Letters, 2017, 8, 5848.[2] S.Y. Shen, X.J. Cheng, C. Wang, X.H. Yan, C.C. Ke, J.W. Yin and J.L. Zhang, Physical Chemistry Chemical Physics, 2017, 19, 26221.[3] Z. F. Zheng, L. X. Luo, F. J. Zhu, X. J. Cheng, F. Yang, S. Y. Shen, G. H. Wei, J. L. Zhang, Electrochim. Acta, 2019, 323, 134751. Acknowledgements This work was supported in part by National Natural Science Foundation of China (21975157) and the National Key Research and Development Program of China (2016YFB0101201 and 2016YFB0101312).

(Invited) The Exploration of Highly Active Pt and Non-Pt Electrocatalysts for the Oxygen Reduction Reaction in PEMFCs

Due to the high Pt loading applied in cathodes of polymer electrolyte membrane fuel cells (PEMFCs), the fuel cell cost remains very high, which greatly hinders its commercialization in different fields. It is well anticipated the Pt loading level should be reduced from the current 0.4 mg/cm2 to less than 0.1 mg/cm2. On the one hand, high active Pt alloy or monolayer catalysts can be obtained by adjusting compositions and structures. On the other hand, the alternative of non-noble metal catalysts (M-N/C, et al.) is considered as the ultimate solution. However, the local mass transfer of oxygen across the active site surface becomes worse due to significant reductions in their amount or activity, seriously affecting the performance of fuel cells1,2. Herein, a series of ultra-low Pt or M-N/C electrocatalysts with both controlled compositions and structures are synthesized and investigated as the oxygen reduction reaction (ORR) electrocatalyst. Corresponding synthetic mechanisms are comprehensively elucidated by advanced physiochemical characterizations combined with density functional theory (DFT). It is believed that the discussion will provide a solid scientific guideline for the development of highly efficiently electrocatalysts for low-cost PEMFCs. Keywords: highly active, low-Pt, non-Pt, oxygen reduction reaction, proton exchange membrane fuel cells, density functional theory Reference [1] W. Xia, A. Mahmood, Z. Liang, R. Zou, S. Guo, Angewandte Chemie International edtion, 2016, 55, 2650.[2] U. Martinez, S.K Babu, E.F. Holby, P. Zelenay, Current Opinion in Electrochemistry, 2018, 9, 224. Acknowledgements This work was supported in part by National Natural Science Foundation of China (21975157) and the National Key Research and Development Program of China (2016YFB0101201 and 2016YFB0101312).

Polyaniline-coated mesoporous Rh films for nonacidic hydrogen evolution reaction

Hydrogen evolution reaction (HER) from water electrolysis in alkaline and neutral media provides a possibility to produce pure hydrogen fuel on a large scale. Therefore, the exploration of highly efficient non-Pt HER electrocatalysts is of great significance. Herein, polyaniline (PANI)-coated mesoporous Rh film on Ni foam is controllably fabricated by a micelle-assisted replacement reaction and the subsequent surface modification. Profiting from the synergetic effect of interconnected mesoporous structure, high electrical conductivity of PANI and the modified electronic structure of Rh, the synthesized mRh@PANI film exhibits superior HER electrocatalytic activity and durability in alkaline and neutral electrolytes. To reach a current density of 50 mA cm−2, low overpotentials of 37 and 69 mV are required in 1 M KOH and 1 M PBS solutions, respectively.

A novel CoN4-driven self-assembled molecular engineering for oxygen reduction reaction

The poor kinetics of oxygen reduction reaction (ORR) invites a quest for the development of low-cost and efficient non-Pt electrocatalysts for fuel cells. Herein, a nanocomposite (g-[Co2N8]) was synthesized by coordination assembly of CoN4 macrocyclic moieties on graphene surface. The CoN4 macrocyclic complex was characterized by UV–Vis, FT-IR, Mass, 1H NMR and 13C NMR spectral studies, whereas UV–Vis, FT-IR, and Mass spectral, Raman, XRD and TEM studies were utilized to characterize the nanocomposite g-[Co2N8]. The results suggested that [CoN4] units are present in self-assembled [Co2N8] species. Further, the nanocomposite g-[Co2N8] was examined for ORR activity by employing cyclic and linear sweep voltammetry and found that the formal potential (E1/2) of g-[Co2N8] (+0.90 V) was more positive than 20% Pt/C (+0.86 V), indicating a remarkable ORR performance of g-[Co2N8] in comparison to 20% Pt/C, followed by 4e-mechanism. Moreover, the nanocomposite (g-[Co2N8]) displayed better ORR activity in comparison to [CoN4] complex which can be attributed to the synergistic incorporation of endo and exo N4–Co2+ moieties in the [Co2N8] species. In addition, g-[Co2N8] electrocatalyst exhibited a comparable stability to 20% Pt/C catalyst after 5000 cycles. This work will help to design multi-metallic coordination polymers with similar or different metal ions in N4-arrangement for various energy related electrocatalysis.

Structural Effectiveness of AgCl-decorated Ag Nanowires Enhancing Oxygen Reduction

In anion exchange membrane fuel cells (AEMFCs) for green energy, silver (Ag)-based compounds are promising non-Pt electrocatalysts with high catalytic activity and a low cost for the oxygen reduction reaction (ORR). Although silver chloride (AgCl) shows high catalytic activity due to the ligand effect originating from the electronegativity difference between the two elements, its low electroconductivity remains a significant issue. Here, we report Ag-AgCl core–shell nanowires decorated with AgCl (AgCl-Ag@AgCl NWs) that have a structure capable of simultaneously exhibiting the good conductivity of a long silver (Ag) core and the high ORR catalytic activity of silver chloride (AgCl). In addition, by decorating AgCl nanoclusters on the AgCl shell, AgCl-Ag@AgCl NWs have an enlarged active surface. As a result, AgCl-Ag@AgCl NWs show highly improved catalytic performance (half-wave potential = 0.78 V vs a reversible hydrogen electrode (RHE), limiting current density = 4.51 mA/cm2). Accelerated durability tests (ADTs) confirm the high stability of AgCl-Ag@AgCl NWs after 4000 cycles of potential sweep and rotating ring disk electrode (RRDE) analysis shows remarkable efficiency with the high electron transfer number (n) (3.97). We also use density functional theory (DFT) calculation to confirm charge transfer, which improves the activity of our catalysts.

Steam activation of Fe-N-C catalyst for advanced power performance of alkaline hydrazine fuel cells

Alkaline hydrazine liquid fuel cells (AHFC) have been highlighted in terms of high power performance with non-precious metal catalysts. Although Fe-N-C is a promising non-Pt electrocatalyst for oxygen reduction reaction (ORR), the surface density of the active site is very low and the catalyst layer should be thick to acquire the necessary number of catalytic active sites. With this thick catalyst layer, it is important to have an optimum pore structure for effective reactant conveyance to active sites and an interface structure for faster charge transfer. Herein, we prepare a Fe-N-C catalyst with magnetite particles and hierarchical pore structure by steam activation. The steam activation process significantly improves the power performance of the AHFC as indicated by the lower IR and activation voltage losses. Based on a systematic characterization, we found that hierarchical pore structures improve the catalyst utilization efficiency of the AHFCs, and magnetite nanoparticles act as surface modifiers to reduce the interfacial resistance between the electrode and the ion-exchange membrane.

Au/Cdot-Nanohybrid Electrocatalyst Synthesized by Rice-Straw-Derived Carbon Dots as a Reducing Agent for Improved Hydrogen Evolution Reactions

We report a facile method by which to synthesize Au/Cdot nanohybrids using carbon dots (Cdots) obtained from rice straw as a direct reducing agent as well as a stabilizer. Rice-straw-derived Cdots possess oxygen-containing functional groups that act as an electron-donating source to reduce Au3+ to Au0 without the use of chemical reagents for the reduction of Au precursors. Additionally, the strong Au-carbon interaction promotes a high electron transfer of the Au/Cdot nanohybrid electrocatalyst, resulting in enhanced performance of the hydrogen evolution reaction (HER). The overpotential is 150 mV at a current density of 10 mA·cm−2 and the TOF value is 0.06·s−1, representing the most outstanding HER performance among Au-based catalysts as a non-Pt HER electrocatalyst. The HER activity is stably maintained for 2000 cycles as well as for 48 h. The synthesis of Cdots, the hybridization of Au/Cdot electrocatalyst, and the production of clean hydrogen fuel using Au/Cdots are zero CO2 emission strategies, not only preventing the emission of pollutants but also satisfying the energy needs of humankind.