Bifunctional Oxygen Electrocatalysis through Chemical Bonding of Transition Metal Chalcogenides on Conductive Carbons

Abstract

performance and commercialization of fuel cells and metal-air batteries. [9,10] Furthermore, searching for bifunctional electrocatalysts for both ORR and OER is critically important for the development of electrochemical devices, especially for rechargeable metal-air batteries. Platinum (Pt) and Pt-based materials are the most efficient ORR catalysts, while ruthenium oxide (RuO 2 ) and iridium oxide (IrO 2 ) are considered as the best electrocatalysts for OER. [11,12] However, the use of these noble metal materials is limited because of their high cost and scarcity. To make matters worse, the efficiency of Pt or RuO 2 / IrO 2 for ORR and OER simultaneously is very poor; this is the case because Pt is only active for ORR (but inactive for OER) while RuO 2 /IrO 2 is only active for OER (but inactive for ORR). [13] Therefore, extensive research efforts have been taken to develop non-noble metal and efficient bifunctional electrocatalysts toward both ORR and OER.In this respect, many kinds of bifunctional electrocatalysts have been investigated, such as alloys of Pt and Ir/Ru catalysts, toward ORR and OER. [14][15][16] However, the high cost of noble metals limits their large-scale applications in electrochemical energy devices. However, earth-abundant conductive carbon materials and their derivatives, such as graphene and carbon nanotubes (CNTs), can replace noble metal alloys for practical applications in electrochemical energy devices. Recently, heteroatom B-and N-doped carbon materials showed the possibility of simultaneous OER and ORR activity. [17][18][19][20][21][22][23][24][25][26][27] However, obtaining OER activity on heteroatom-doped carbon materials is still challenging because of the low catalytic activity of water splitting; additionally, although the ORR activity can match commercial Pt/C catalysts, it suffers from poor stability. [28,29] In order to address this challenge, composites of transition metals, including cobalt oxide/cobalt sulphide and carbon materials, have been proposed to actively catalyze OER with low overpotentials. [30][31][32] Moreover, a metal-doped transition metal oxide on graphene has also been shown to be a good electrocatalyst toward OER. [33][34][35][36] However, developing carbon-based electrocatalysts toward ORR and OER is still challenging due to the instability of transition metals and the nonintimate contact between the conductive carbonaceous materials and the doping/decorated active material. [37] Improving the electrochemical performance of both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has been of great interest in emerging renewable energy technologies. This study reports an advanced bifunctional hybrid electrocatalyst for both ORR and OER, which is composed of tungsten disulphide (WS 2 ) and carbon nanotube (CNT) connected via tungsten carbide (WC) bonding. WS 2 sheets on the surface of CNTs provide catalytic active sites for electrocatalytic activity while the CNTs act as conduction channels and provide a large surface area. Moreover,...

Composite Metal Oxide‐Carbon Nanotube Electrocatalysts for the Oxygen Evolution and Oxygen Reduction Reactions

“…[16][17][18] Functionalizing CNTs with suitable OER and ORR catalysts could therefore be a feasible approach to overcome the inherent low catalytic activity of CNTs. [19] The resulting metal oxide/CNT nanocomposites have thus been proposed as promising OER catalysts with low overpotentials and ORR catalysts with high half-wave potentials. [20,21] To optimize catalytic performance, doping of the metal oxide catalysts with additional metal atoms has been put forward as a means of controlling the physical and electronic structure of the composite.…”

Recent Advances and Prospects of Metal‐Based Catalysts for Oxygen Reduction Reaction

“…[110][111][112] Tiwari et al prepared an advanced dual-functional electrocatalyst by combining tungsten disulfide (WS 2 ) and CNTs through tungsten carbide (WC) bonds. [113] The WS 2 flakes on the surface of CNTs provide catalytically active sites, and the CNTs act as conduction channels to provide a larger surface area for oxygen transport. The newly formed WC crystal structure provides a simple pathway for electron spin coupling transfer and improves stability and electrocatalytic activity.…”

“…In recent years, a variety of transition metal chalcogenides (M—X, where M = Co, Ru, Re, or Rh and X = S, Se, or Te) have begun to be used as ORR catalysts and show excellent performance . Tiwari et al prepared an advanced dual‐functional electrocatalyst by combining tungsten disulfide (WS 2 ) and CNTs through tungsten carbide (WC) bonds . The WS 2 flakes on the surface of CNTs provide catalytically active sites, and the CNTs act as conduction channels to provide a larger surface area for oxygen transport.…”

Transition‐Metal Oxides/Carbides@Carbon Nanotube Composites as Multifunctional Electrocatalysts for Challenging Oxidations and Reductions

“…Kinetic analyses gave Ta fel slopes of 321, 343, 300, and 451 mV dec À1 for 1-600, 1-750, 1-900,a nd Pt/C (20 wt %) respectively (see Figure S13). [55,56] For ad etailed comparison, see Ta ble 1a nd Ta ble S1. From the comparison of LSV ( Figure S11) and CV ( Figure S14) analyses beforea nd after chronoamperometry,only slight potentialshifts were observed, which highlights the long-term stability and high chemical resistance of the materials under acidic conditions.…”

“…Finally,w ea nalyzed the potentiald ifferenceb etween OER and ORR (DE OERÀORR )i n0 .1 m aqueous KOH for the composites reported:t he smallest potential difference was observed for 1-900 (DE OERÀORR = 0.78 V), which is significantlyl ower than various noble-metal-based references such as 20 wt %P t/C (1.16 V), 20 wt %I r/C (0.92 V), [52] 20 wt %R u/C (1.01 V), [53] IrO 2 (1.11V), [54] RuO 2 (1.30 V), [19] as well as variousm etal-free carbon-nanotube-based materials and transition-metal oxide modified carbon materials. [55,56] For ad etailed comparison, see Ta ble 1a nd Ta ble S1. In summary,t he as-prepared composites acted as ah ighly active and highlys table bifunctionale lectrocatalystfor both OER and ORR.…”