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Hydrogen energy is regarded as an auspicious future substitute to replace fossil fuels, due to its environmentally friendly characteristics and high energy density. In the pursuit of clean hydrogen production, there has been a significant focus on the advancement of effective electrocatalysts for the process of water splitting. Although noble metals like Pt, Ru, Pd and Ir are superb electrocatalysts for the hydrogen evolution reaction (HER), they have limitations for large-scale applications, mainly high cost and low abundance. As a result, non-precious transition metals have emerged as promising candidates to replace their more expensive counterparts in various applications. This review focuses on recently developed transition metal phosphides (TMPs) electrocatalysts for the HER in alkaline media due to the cooperative effect between the phosphorus and transition metals. Finally, we discuss the challenges of TMPs for HER. [ABSTRACT FROM AUTHOR]

Hydrogen is considered a future energy carrier that could improve energy storage of intermittent solar/wind power to solve energy and environmental problems. Based on such demand, development of electrocatalysts for hydrogen generation has been actively pursued. Although Pt is the most efficient catalyst for the hydrogen evolution reaction (HER), it has limits for widespread application, mainly its low abundance and high cost. Thus, developing an efficient catalyst from non‐precious metals that are abundant and inexpensive remains an important challenge to replacement of Pt. Transition metals have been considered possible candidates to replace Pt‐based catalysts. In this review, among the transition metals, we focus on recently developed molybdenum–carbon (Mo–C) hybrid materials as electrocatalysts for HER. In particular, the synthesis strategy for Mo–C hybrid electrocatalysts and the role of various carbon nanocomposites in Mo–C hybrid systems are highlighted. Going hybrid for hydrogen: This review focuses on recently developed molybdenum–carbon (Mo–C) hybrid materials as electrocatalysts for the hydrogen evolution reaction (HER). In particular, the synthesis strategy for Mo‐C hybrid electrocatalysts and the role of various carbon nanocomposites in Mo‐C hybrid systems are highlighted. [ABSTRACT FROM AUTHOR]

Abstract: Development of cost‐effective and efficient electrocatalysts for the oxygen reduction reaction (ORR) is one of the most important topics in the polymer electrolyte membrane fuel cells (PEMFCs). Herein, we suggested the enhanced electrochemical catalyst with nanoscale platinum anchored on iron (Fe) and nitrogen (N) co‐doped graphene nanoplatelets (Pt/FeN‐GnPs) with low content of Pt. The nanoscale platinum particles are uniformly anchored on the surface of FeN‐GnPs and result in excellent oxygen reduction activity and stability in acidic media. The fascinating interaction between Pt particles and FeN−GnPs substrate contributed to advanced oxygen reduction activity, outstanding cell performance, and remarkable high stability for acidic PEM fuel cells. [ABSTRACT FROM AUTHOR]

Kish graphite, a waste (called dust) from a steelmaking process, can be simultaneously purified and functionalized by mechanochemical ball-milling in the presence of iodine. The resultant iodinated Kish graphite (I-Kish-G) contains low content of impurities and high iodine content (1.83 at%, 16.17 wt%, energy dispersive X-ray spectroscopy) with high crystallinity. It has high specific surface area (924.3 m2 g−1), indicating that I-Kish-G is significantly purified, functionalized, and exfoliated into a few graphitic layers. More importantly, I-Kish-G displays outstanding electrocatalytic activity for oxygen reduction reaction with long-term durability and robustness against methanol crossover and CO poisoning effects in alkaline media. [ABSTRACT FROM AUTHOR]

Hierarchically structured nitrogen-doped carbon nanotube (NCNT) composites, with copper (Cu) nanoparticles embedded uniformly within the nanotube walls and cobalt oxide (Co xO y) nanoparticles decorated on the nanotube surfaces, are fabricated via a combinational process. This process involves the growth of Cu embedded CNTs by low- and high-temperature chemical vapor deposition, post-treatment with ammonia for nitrogen doping of these CNTs, precipitation-assisted separation of NCNTs from cobalt nitrate aqueous solution, and finally thermal annealing for Co xO y decoration. Theoretical calculations show that interaction of Cu nanoparticles with CNT walls can effectively decrease the work function of CNT surfaces and improve adsorption of hydroxyl ions onto the CNT surfaces. Thus, the activities of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are significantly enhanced. Because of this benefit, further nitrogen doping, and synergistic coupling between Co xO y and NCNTs, Cu@NCNT/Co xO y composites exhibit ORR activity comparable to that of commercial Pt/C catalysts and high OER activity (outperforming that of IrO2 catalysts). More importantly, the composites display superior long-term stability for both ORR and OER. This simple but general synthesis protocol can be extended to design and synthesis of other metal/metal oxide systems for fabrication of high-performance carbon-based electrocatalysts with multifunctional catalytic activities. [ABSTRACT FROM AUTHOR]

One feasible alternative to Pt catalyst in dye-sensitized solar cells (DSSCs) is metalloid tellurium (Te)-doped graphene nanoplatelets (TeGnPs). These were prepared by ball-milling graphite in the presence of Te crystals. Introduction of Te at the edges of TeGnPs was confirmed with various analytical techniques including time of flight secondary ion mass spectrometry (TOF-SIMS). The resultant TeGnPs are herein evaluated as counter electrode (CE) materials for the cobalt reduction reaction (CRR) in DSSCs. TeGnP-CE exhibits much lower charge transfer resistance ( R ct =0.15 Ω cm 2 ) than that ( R ct =1.77 Ω cm 2 ) of Pt-CE. More importantly, TeGnP-CE displays an extreme electrochemical stability for the Co(bpy) 3 2+/3+ (bpy=2,2'-bipyridine) redox couple even after 1000 potential cycles. The SM315-based DSSC fabricated with TeGnP-CE shows a better power conversion efficiency (PCE=11.58%) than that with Pt-CE (11.03%), suggesting that TeGnP-CE could be one of the best alternatives to Pt-CE in DSSCs. [ABSTRACT FROM AUTHOR]

Iodination of carbon-based materials is known to improve their electrocatalytic activity for oxygen reduction reaction. Here, we report iodination of activated charcoal by mechanochemical ball-milling activated charcoal (AcC) in the presence of iodine (I 2 ). The electrodes fabricated from the resultant iodinated AcC (IAcC) show efficient metal-free electrocatalytic activity for fuel cells and hybrid Li-air cells. In addition to iodination, the ball-milling can not only purify AcC but also change morphology. The iodine content in IAcC reaches as high as 0.59 at.% (5.8 wt.%), the amorphous powder-type morphology of the starting AcC has been changed to the flake-type sheets of the resulting IAcC, and metallic impurities in the IAcC are substantially reduced. The results indicate that the mechanochemical ball-milling simultaneously induces functionalization, structural restoration and purification. Furthermore, the IAcC is readily dispersible in various polar solvents, allowing the fabrication of electrodes via solution processing. The metal-free IAcC cathodes exhibited outstanding electrocatalytic activities for fuel cells and hybrid Li-air cells with higher selectivity, longer-term stability and better tolerance to methanol crossover/CO poisoning effects than the starting AcC and comparable with commercial Pt/C counterparts. [ABSTRACT FROM AUTHOR]

Oxygen functional groups play a key role in vanadium redox reactions. To identify the effective location of oxygen functionalities in graphene-based nanomaterials, a selectively edge-functionalized graphene nanoplatelet (E-GnP) with a crystalline basal plane is produced by a ball-milling process in the presence of dry ice. For comparison, the reduced graphene oxide (rGO) that contains defects at both edges and in the basal plane is produced by a modified Hummers' method. The location of defects in the graphene-based nanomaterials significantly affects the electrocatalytic activity towards vanadium redox couples (V2+/V3+ and VO2+/VO2 +). The improved activity of these nanoplatelets lies in the presence of oxygen defects at the edge sites and higher crystallinity of basal planes than in rGO. This effective location of oxygen defects facilitates fast electron-transfer and mass-transport processes. [ABSTRACT FROM AUTHOR]

Doping with foreign atoms is a powerful technique for modifying the inherent properties of a host materials. In this work, we report a strategy for preparing multiple heteroatom-doped graphene nanoplatelets (GnPs). Poly(anilineboronic acid, PABA), which is one of the conducting polymers, was in-situ grafted to edge-amine functionalized GnPs (A-GnPs) in phosphoric acid. The isolated PABA grafted A-GnPs phosphoric acid salts (PA-GnP salts) were heat-treated at 900 °C under argon atmosphere to yield boron (B)-nitrogen (N)-phosphorus (P) doped GnPs (BNP-GnPs). The structure of the BNP-GnPs was confirmed by various techniques, including transmission electron microscopy, scanning electronic microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and thermogravimetric analysis. The BNP-GnPs demonstrated significantly improved electrocatalytic activity towards the oxygen reduction reaction, suggesting that BNP-GnPs can be one of the best alternatives to precious Pt-based electrocatalysts. [ABSTRACT FROM AUTHOR]