Comparison of cobalt complex catalysts having a fourteen-membered ring structure and conventional sixteen-ones for oxygen reduction and hydrogen evolution reactions

SummaryEfficient electrocatalyst toward hydrogen evolution/oxidation reactions (HER/HOR) and oxygen reduction reaction (ORR) is desirable for water splitting, fuel cells, etc. Herein, we report an advanced platinum phosphide (PtP2) material with only 3.5 wt % Pt loading embedded in phosphorus and nitrogen dual-doped carbon (PNC) layer (PtP2@PNC). The obtained catalyst exhibits robust HER, HOR, and ORR performance. For the HER, a much low overpotential of 8 mV is required to achieve the current density of 10 mA cm−2 compared with Pt/C (22 mV). For the HOR, its mass activity (MA) at an overpotential of 40 mV is 2.3-fold over that of the Pt/C catalyst. Interestingly, PtP2@PNC also shows exceptional ORR MA which is 2.6 times higher than that of Pt/C and has robust stability in alkaline solutions. Undoubtedly, this work reveals that PtP2@PNC can be employed as nanocatalysts with an impressive catalytic activity and stability for broad applications in electrocatalysis.

Many efficient and non-precious metal catalysts for oxygen reduction or hydrogen evolution reactions have been developed, but bifunctional catalysts for both oxygen reduction reaction and hydrogen evolution reactions are seldom reported despite their advantages. Herein, we designed the bulk preparation of heteroatom-doped nanoporous carbon catalysts using widely available and recyclable Pueraria lobata powder as the carbon source. The typical product was N, P and Fe Tri-doped nano-porous carbon (N,P,Fe-NPC) with high surface area (BET surface area of 776.68 m2 g−1 and electrochemical surface area of 55.0 mF cm−2). The typical N,P,Fe-NPC sample simultaneously exhibited high activities for oxygen reduction and hydrogen evolution reactions. Because of the high surface area and the tri-doping of N, P and Fe elements, the prepared material may have applications in other fields such as gas uptake, sensors, sewage treatment, and supercapacitors. The suggested approach is low-cost, simple and readily scalable.

The development of efficient, durable and commercially competitive catalysts for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is undoubtedly a challenging task for fuel cell technology. In this context, for the first time, we developed a bi-metallic heterogeneous nanocatalyst (NC) comprising high-density atomic SnOx-clusters anchored Pt-nanorods (denoted as SnOx@Pt) via formic acid reduction method (FAM) as a bifunctional catalyst for ORR and HER (Fig.1). The as-prepared SnOx@Pt nanorods exhibit unprecedented high mass activity (MA) of 160 mAmg-1 (Pt) at 0.85 V vs RHE in acidic ORR (0.5M HClO4), which outperformed the commercial J.M.-Pt/C (20 wt.% Pt) catalyst by 1.4 folds. Of special relevance, SnOx@Pt nanorods exhibit remarkable durability when operated up to 5000 cycles in accelerated durability test (ADT) and retain their 87% MA as that of the initial condition. Additionally, as-prepared SnOx@Pt nanorods demonstrated a notable lower overpotential (η) of 48 mV at the cathodic current density of 10 mAcm-2 and the Tafel slope of 33 mVdec -1 in acidic HER (0.5M H2SO4). These overpotential and Tafel slope values are significantly lower compared to commercial J.M.-Pt/C catalyst (η = 60 mV and Tafel slope = 38 mVdec-1). Moreover, such material retained its 100% performance in the chronoamperometric (CA) stability test up to 6h, which shows its capability in potential commercialization. The cross-referencing results of physical inspections and electrochemical analysis reveal that such a high-performance of SnOx@Pt nanorods is attributed to the local synergetic collaboration between SnOx modifiers and neighboring Pt active sites. More specifically, the SnOx modifiers promote the H-OH bond cleavage during HER, while simultaneously promotes the desorption of oxygen species on Pt surface in ORR, which later triggers the reduction reaction performances. Meanwhile, SnOx provides a shielding effect to Pt during harsh reduction conditions and thus high stability of SnOx@Pt nanorods is achieved. Of utmost importance, this study not only unveils a novel geometric design but also provides the mechanistic understanding behind the superior electrochemical properties of the unique SnOx modifiers in ORR and HER. Hence, we envision that the proposed rationale will be a forwarding step for the development of high-performance low Pt content catalysts for fuel cells with superior electrochemical properties far beyond the physical nature of transition elements. Keywords: Oxygen reduction reaction, hydrogen evolution reaction, fuel cells, nanocatalysts, mass activity

Hierarchically Porous Co3C/Co-N-C/G Modified Graphitic Carbon: A Trifunctional Corrosion-Resistant Electrode for Oxygen Reduction, Hydrogen Evolution and Oxygen Evolution Reactions

Both electrocatalytic water splitting and hydrogen proton-exchange membrane fuel cells are key green technologies to achieve a carbon-neutral future. Their half reactions of these technologies including hydrogen evolution reaction and oxygen reduction reaction rely heavily on Pt/C as the electrocatalysts to overcome the sluggish kinetics. However, Pt/C suffering from poor stability as well as its high price and scarcity have made fabricating active and durable electrocatalysts a pressing need. Both multi-component disordered alloys and binary intermetallic compounds have received wide research attention as potential electrocatalysts. Crystal structure plays an important role in electrocatalytic activity. However, multi-component intermetallic compounds have been rarely explored and the effects of ordering crystal structure on catalytic activity largely remain unknown. In this study, we fabricate a series of intermetallic Pt4FeCoCuNi nanoparticles with tunable ordering degrees. Using localized aberration-corrected STEM, we investigate how the multi-component disordered alloy nanoparticle transforms into the ordered intermetallic nanoparticle at the single-particle level, which agrees with macroscopic analysis by SAED and XRD. Then we illustrate the relation between its crystal structure, electronic structure, and electrocatalytic performance. The highly ordered multi-component intermetallics show a downshifted d-band center and therefore weakened adsorption for H and O compared with Pt/C. As a result, it exhibits enhanced electrocatalytic performance for oxygen evolution, oxygen reduction, and hydrogen evolution reactions. Besides optimized electronic structure, the enhanced alkaline hydrogen evolution reactivity can also result from promoted water disassociation by surface FeCoCuNi-based oxides/hydroxides. Owing to the entropy increment resulting from multi-elemental mixing and shortened bond length, it also shows the considerably increased durability for hydrogen evolution and oxygen reduction reactions. Here, by using combined intermetallic stabilization strategies and high-entropy stabilization strategies, we successfully resolve the long-standing stability concerns of Pt electrocatalysts for HER in alkaline and ORR. This structure-property relation will provide insight for designing efficient and robust electrocatalysts and stimulate the synthesis of more multi-component intermetallics.

Cobalt-nitrogen-doped graphdiyne as an efficient bifunctional catalyst for oxygen reduction and hydrogen evolution reactions

Using density functional theory calculations, a set of candidate nanoparticle catalysts are identified based on reactivity descriptors and segregation energies for the oxygen reduction and hydrogen evolution reactions. Trends in the data were identified by screening over 700 core@shell 2 nm transition metal nanoparticles for each reaction. High activity was found for nanoparticles with noble metal shells and a variety of core metals for both reactions. By screening for activity and stability, we obtain a set of interesting bimetallic catalysts, including cases that have reduced noble metal loadings and a higher predicted activity as compared to monometallic Pt nanoparticles.

Empirical analysis and recent advances in metal-organic framework-derived electrocatalysts for oxygen reduction, hydrogen and oxygen evolution reactions

Catalytic activity of 2D MXenes toward electroreduction processes: Oxygen reduction and hydrogen evolution reactions

Successful synthesis of gold nanoparticles incorporated in a zinc‐based metal‐organic framework (Au@Zn‐MOF) is reported in this paper. The synthesis of Au@Zn‐MOF is confirmed by UV‐Vis, FT‐IR and X‐ray photoelectron spectroscopy (XPS) studies. The Au@Zn‐MOF catalyst demonstrates electrocatalytic activity towards the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER). The relative catalytic performance of Au@Zn‐MOF towards ORR and HER has been studied under acidic condition. ORR proceeds via a two electron and two proton mechanism with hydrogen peroxide as the end product, while HER follows the Volmer mechanism i. e., adsorption of H+ on the catalyst's active sites. Au@Zn‐MOF exhibits an ORR onset potential of 0.45 V (vs. RHE) with two different Tafel slopes, −93 and −103.6 mV in acidic solution. Further, an excellent catalytic activity is observed for HER with an onset potential of 0.02 V (vs. RHE) and a Tafel slope of 87 mV in N2 saturated 0.1 M HClO4 solution. However, in O2 saturated 0.1 M HClO4 solution, a HER onset potential of 0.04 V (vs. RHE) is observed with two different Tafel slopes, 610 and 220 mV. The value of Tafel slopes in the presence of O2 advocates the diminution of the ORR activity because of the HER. Thus, Tafel slope values of HER and ORR suggest that protons and O2 compete to reach the electrode surface for getting reduced.

Co@Pd core-shell nanoparticles embedded in nitrogen-doped porous carbon as dual functional electrocatalysts for both oxygen reduction and hydrogen evolution reactions

Cobalt single atom site isolated Pt nanoparticles for efficient ORR and HER in acid media

Phase-mediated cobalt phosphide with unique core-shell architecture serving as efficient and bifunctional electrocatalyst for hydrogen evolution and oxygen reduction reaction

The rational design of multi-functional catalysts that use non-noble metals to facilitate the interconversion between H2, O2 and H2O is an intense area of investigation. Bimetallic nanosystems with highly tunable electronic, structural and catalytic properties that depend on their composition, structure, and size have attracted considerable attention. Herein, we report the synthesis of bimetallic nickel-copper (NiCu) alloy nanoparticles confined in a sp2 carbon framework that exhibits tri-functional catalytic properties towards hydrogen evolution (HER), oxygen reduction (ORR) and oxygen evolution (OER) reactions. The electrocatalytic functions of the NiCu nanoalloys were experimentally and theoretically correlated with the composition-dependent local structural distortion of the bimetallic lattice at the nanoparticle surfaces. Our study demonstrated a downshift of the d-band of the catalysts that adjusts the binding energies of the intermediate catalytic species. XPS analysis revealed that the binding energy for Ni 2p3/2 band of the Ni0.25Cu0.75/C nanoparticles were shifted ~three times compared to other bimetallic systems and this was correlated to the high electrocatalytic activity observed. Interestingly, the bimetallic Ni0.25Cu0.75/C catalyst surpassed the OER performance of RuO2 benchmark catalyst exhibiting a small onset potential of 1.44 V vs RHE and an overpotential of 400 mV at 10 mA·cm-2 as well as the electrochemical long-term stability of commercial RuO2 and Pt catalysts and kept at least 90% of the initial current applied after 20000s for the OER/ORR/HER reactions. This study reveals significant insight about the structure-function relationship for non-noble bimetallic nanostructures with multifunctional electrocatalytic properties.

Oxygen Reduction and Hydrogen Evolution Reactions on Zigzag ReS2 Nanoribbons