Ruthenium triazine composite: a good match for increasing hydrogen evolution activity through contact electrification

The development of Pt‐free catalysts for the alkaline hydrogen evolution reaction (HER), which is widely used in industrial scale water‐alkali electrolyzers, remains a contemporary and pressing challenge. Ruthenium (Ru) has excellent water‐dissociation abilities and could be an alternative water splitting catalyst. However, its large hydrogen binding energy limits HER activity. Here, a new approach is proposed to boost the HER activity of Ru through uniform loading of Ru nanoparticles on triazine‐ring (C3N3)‐doped carbon (triNC). The composite (Ru/triNC) exhibits outstanding HER activity with an ultralow overpotential of ≈2 mV at 10 mA cm−2; thereby making it the best performing electrocatalyst hitherto reported for alkaline HER. The calculated metal mass activity of Ru/triNC is >10 and 15 times higher than that of Pt/C and Pt/triNC. Both theoretical and experimental studies reveal that the triazine‐ring is a good match for Ru to weaken the hydrogen binding on Ru through interfacial charge transfer via increased contact electrification. Therefore, Ru/triNC can provide the optimal hydrogen adsorption free energy (approaching zero), while maintaining the strong water‐dissociation activity. This study provides a new avenue for designing highly efficient and stable electrocatalysts for water splitting

S, N dual-doped porous carbon materials derived from biomass for Na ion storage and O-2 electroreduction

Heteroatom-doped porous carbon materials have been widely reported in electrochemistry, but low-cost carbon sources and facile synthesis strategy are still highly in demand. Herein, N, S dual-doped porous carbon materials (CDNSPCs) were synthesized by carbonizing and etching pollution source-carrageenan, which shows great potentials as anodes for sodium-ion batteries (SIBs) and electrocatalysts for oxygen reduction reaction (ORR). Using K-, I- or lambda-type carrageenan as precursor, three carbon samples (CDNSPC-1, -2, or -3) were obtained, respectively. Among them, CDNSPC-3 with the highest sulfur content exhibits an initial discharge capacity of 1505 mAh g(-1) at 0.05 A g(-1), a high specific capacity of 85 mAh g(-1) at 10 A g(-1), and a capacity of 171 mAh g(-1) at 1.0 A g(-1) after 400 cycles. Moreover, it also exhibits excellent ORR activity with relatively positive E-onset (0.88 V vs RHE) and a four-electron dominant pathway, much better than CDNSPC-1 and CDNSPC-2. The high sulfur content in the precursor could efficiently promote the activation by combining metal ions of activating agents and sulfur-containing groups at high temperature. The present strategy is low-cost and eco-friendly, opening a new avenue for the sustainable development of valuable materials from pollutants

Nitrogen-doped carbon spheres decorated with CoSx nanoparticles as multifunctional electrocatalysts for rechargeable zn-air battery and overall water splitting

Developing non-precious multi-functional electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) to replace noble metal (Pt, Ru, Ir, etc) is one of the most important directions in the field of energy conversion and storage. Herein, we successfully prepared CoSx nanoparticles loaded onto N-doped carbon spheres to form unique CoSx/NCS nanocomposites, showing good trifunctional activities for ORR, OER and HER. As the cathodic electrocatalyst in Zn-air battery, the CoSx/NCS shows a lower charge voltage of 2.1 V and a high power density of 72.7 mW cm(-2) compared to Pt/C. CoSx/NCS also shows potentials in overall water splitting as the OER and HER electrocatalysts. The onset potential and overpotential at 10 mA cm(-2) toward overall water splitting reaches 1.70 V and 1.83 V, respectively. The enhanced activity of CoSx/NCS should be ascribed to the synergistic effects of improved surface hydrophilicity, CoN sites, pyridinic-N species, and Co-S bonds. This study provides a new strategy to synthesize active electrocatalysts with multiple functions in energy conversion and storage

Highly Localized C-N2 Sites for Efficient Oxygen Reduction

The search for oxygen reduction reaction (ORR) catalysts outperforming Pt, the state-of-the-art material, continues. Doped carbon-based materials offer a viable means for replacing Pt, but their activity improvement still remains a great challenge. Here, configurations of N-doped carbons are first analyzed using ab initio simulations toward ORR. The results show that a certain short-range ordered structure labeled as C-N2, which comprises of two nitrogen atoms flanking carbon, is the optimal choice. The predicted configuration of C-N2 is experimentally realized by triazine-doped carbon (triNC). The triNC with C-N2 sites demonstrates high ORR activity (onset potential 0.98 V, halfwave potential 0.89 V) comparable to commercial 20% Pt/C. The highly localized and positive-charged carbon atom in the C-N2 structure facilitates the dissociation of O-2 to increase the ORR kinetics, proved by theoretical calculation. A Zn-air cathode is fabricated using the triNC ORR electrocatalyst and outperforms the cathode using Pt/C in terms of specific capacity, energy density and long-term durability. The atomic-scale approach reported here provides a good strategy to achieve active carbon-based electrocatalysts for potential and scalable use in energy conversion and storage

Edge-sited Fe-N-4 atomic species improve oxygen reduction activity via boosting O-2 dissociation

The development of low-cost, efficient, and stable electrocatalysts toward the oxygen reduction reaction (ORR) is urgently demanded for scalable applications in fuel cells or zinc-air batteries (ZABs), but still remains a challenge. Herein, carbon materials with edge-sited Fe-N-4 atomic species (E-FeNC) were synthesized from pyrolysis of abundant Fe-containing biomass using silica spheres as hard template. The E-FeNC delivers remarkable ORB. performance with a half-wave potential of 0.875 V (vs. reversible hydrogen electrode (RHE)), much better than Pt/C (0.859 V), attributed to atomically dispersed Fe-N-4 moieties nearby graphitic edges. The density functional calculations reveal that O-2 molecule adsorbs on Fe-N-4 sites with an energetically favorable side-on configuration with elongated O=O bond rather than end-on form, boosting the subsequent dissociation pathway with a direct 4e reaction route. Using E-FeNC as cathode catalyst, the primary ZAB exhibits high specific capacity of 710 mA h g(-1) and power density of 151.6 mW cm(-2) . The rechargeable ZAB by coupling E-FeNC and NiFe layered double hydroxide (LDH) demonstrates long-term capacity retention over 200 h, superior to that using noble Pt/C and RuO2. This unique carbon material with atomically dispersed metal sites opens up an avenue for the design and engineering of electrocatalysts for energy conversion systems

Mechanochemical synthesis of multi-site electrocatalysts as bifunctional zinc-air battery electrodes

Mechanochemical synthesis of multi-site electrocatalysts as bifunctional zinc-air battery electrode

Ruthenium Triazine Composite: A Good Match for Increasing Hydrogen Evolution Activity through Contact Electrification

The development of Pt-free catalysts for the alkaline hydrogen evolution reaction (HER), which is widely used in industrial scale water-alkali electrolyzers, remains a contemporary and pressing challenge. Ruthenium (Ru) has excellent water-dissociation abilities and could be an alternative water splitting catalyst. However, its large hydrogen binding energy limits HER activity. Here, a new approach is proposed to boost the HER activity of Ru through uniform loading of Ru nanoparticles on triazine-ring (C3N3)-doped carbon (triNC). The composite (Ru/triNC) exhibits outstanding HER activity with an ultralow overpotential of approximate to 2 mV at 10 mA cm(-2); thereby making it the best performing electrocatalyst hitherto reported for alkaline HER. The calculated metal mass activity of Ru/triNC is >10 and 15 times higher than that of Pt/C and Pt/triNC. Both theoretical and experimental studies reveal that the triazine-ring is a good match for Ru to weaken the hydrogen binding on Ru through interfacial charge transfer via increased contact electrification. Therefore, Ru/triNC can provide the optimal hydrogen adsorption free energy (approaching zero), while maintaining the strong water-dissociation activity. This study provides a new avenue for designing highly efficient and stable electrocatalysts for water splitting

Bottom-up evolution of perovskite clusters into high-activity rhodium nanoparticles toward alkaline hydrogen evolution

Self-reconstruction is an efficient method to synthesize active electrocatalysts. Here, the authors demonstrate a bottom-up evolution route of electrochemically reducing Cs3Rh2I9 halide-perovskite clusters to prepare ultrafine Rh nanoparticles with multiply sites for alkaline hydrogen evolution