We developed two-step solution-phase reactions to form hybrid materials of Mn3O4 nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Mn3O4 nanoparticles grown selectively on RGO sheets over free particle growth in solution allowed for the electrically insulating Mn3O4 nanoparticles wired up to a current collector through the underlying conducting graphene network. The Mn3O4 nanoparticles formed on RGO show a high specific capacity up to ~900mAh/g near its theoretical capacity with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn3O4 nanoparticles grown atop. The Mn3O4/RGO hybrid could be a promising candidate material for high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for design and synthesis of battery electrodes based on highly insulating materials.

Mn3O4-Graphene Hybrid as a High Capacity Anode Material for Lithium Ion Batteries

Electrocatalysis plays a key role in the energy conversion processes central to several renewable energy technologies that have been developed to lessen our reliance on fossil fuels. However, the best electrocatalysts for these processes—which include the hydrogen evolution reaction (HER), the oxygen reduction reaction (ORR), and the redox reactions that enable regenerative liquid-junction photoelectrochemical solar cells—often contain scarce and expensive noble metals, substantially limiting the potential for these technologies to compete with fossil fuels. The considerable challenge is to develop robust electrocatalysts composed exclusively of low-cost, earth-abundant elements that exhibit activity comparable to that of the noble metals. In this review, we summarize recent progress in the development of such high-performance earth-abundant inorganic electrocatalysts (and nanostructures thereof), classifying these materials based on their elemental constituents. We then detail the most critical obstacles facing earth-abundant inorganic electrocatalysts and discuss various strategies for further improving their performance. Lastly, we offer our perspectives on the current directions of earth-abundant inorganic electrocatalyst development and suggest pathways toward achieving performance competitive with their noble metal-containing counterparts.

Earth-abundant inorganic electrocatalysts and their nanostructures for energy conversion applications

Titanium dioxide (TiO2) has been the most intensively investigated binary transition metal oxide in the past four decades as indicated by Figure S1. Furthermore, the annual number of papers published on TiO2 has seen a continuous increase, particularly since the beginning of this century (Figure S2). This is understandable when one considers the wide range of applications of TiO2 from the conventional areas (i.e., pigment, cosmetic, toothpaste, and paint) to the later developed functional areas such as photoelectrochemical cell,(1-3) dye-sensitized solar cells (DSSCs),(4-11) photocatalysis,(12-24) catalysis,(25-31) photovoltaic cell,(32-34) lithium ion batteries,(35-41) sensors,(42-46) electron field emission,(47-51) microwave absorbing material, biomimetic growth, and biomedical treatments.(52-57) Nearly all these functional applications of TiO2 fall in the scope of energy, environment, and health, which are definitely the three most important and challenging themes facing the Human race that need to be addressed in this century. Besides the apparent merits including nontoxicity, elemental abundance, good chemical stability, and easy synthesis, TiO2 has attracted strong research interest worldwide due to its physicochemical properties for realizing various functions.(15, 58, 59) Especially, very encouraging progresses in photocatalysis and DSSCs with the involvement of TiO2 have greatly stimulated the rapid development of TiO2 crystals with controllable phase, size, shape, defect, and heteroatom.(58, 60-68)

Titanium dioxide crystals with tailored facets

TiO2 photocatalyst for water treatment applications

Basic concepts and recent advances in nitrophenol reduction by gold- and other transition metal nanoparticles

Activated porous carbon prepared from paulownia flower for high performance supercapacitor electrodes

Chemically grafted graphene-polyaniline composite for application in supercapacitor

Porous Co3S4@Ni3S4 heterostructure arrays electrode with vertical electrons and ions channels for efficient hybrid supercapacitor

Activated N-doped porous carbons (a-NCs) were synthesized by pyrolysis and alkali activation of graphene incorporated melamine formaldehyde resin (MF). The moderate N doping levels, mesopores rich porous texture, and incorporation of graphene enable the applications of a-NCs in surface and conductivity dependent electrode materials for supercapacitor and dye-sensitized solar cell (DSSC). Under optimal activation temperature of 700 °C, the afforded sample, labeled as a-NC700, possesses a specific surface area of 1302 m2 g(-1), a N fraction of 4.5%, and a modest graphitization. When used as a supercapacitor electrode, a-NC700 offers a high specific capacitance of 296 F g(-1) at a current density of 1 A g(-1), an acceptable rate capability, and a high cycling stability in 1 M H2SO4 electrolyte. As a result, a-NC700 supercapacitor delivers energy densities of 5.0-3.5 Wh kg(-1) under power densities of 83-1609 W kg(-1). Moreover, a-NC700 also demonstrates high electrocatalytic activity for I3- reduction. When employed as a counter electrode (CE) of DSSC, a power conversion efficiency (PCE) of 6.9% is achieved, which is comparable to that of the Pt CE based counterpart (7.1%). The excellent capacitive and photovoltaic performances highlight the potential of a-NCs in sustainable energy devices.

Nitrogen-Doped Porous Carbons As Electrode Materials for High-Performance Supercapacitor and Dye-Sensitized Solar Cell.

Mesocrystalline Cu2O hollow nanocubes (MCHNs) were successfully prepared by a facile reduction reaction under room temperature. CuCl2 played a dual role as both copper source and morphology controlling reagent for the oriented aggregation of primary Cu2O crystallites toward MCHNs. Due to the high crystallinity and high specific surface area, the as-prepared MCHNs exhibited high electrocatalytic activity for the reduction of hydrogen peroxide (H2O2) and oxidation of glucose. The non-enzymatic amperometric biosensors based on the MCHNs demonstrated a detection limit of 1.03 μM and a sensitivity of 156.6 μA mM−1 for H2O2, as well as a detection limit of 0.87 μM and sensitivity of 52.5 μA mM−1 for glucose. The high sensitivities and anti-interference ability made the MCHNs a promising material in non-enzymatic biosensors.

Jiuli Chang

Papers

Activated porous carbon prepared from paulownia flower for high performance supercapacitor electrodes

Chemically grafted graphene-polyaniline composite for application in supercapacitor

Porous Co3S4@Ni3S4 heterostructure arrays electrode with vertical electrons and ions channels for efficient hybrid supercapacitor

Nitrogen-Doped Porous Carbons As Electrode Materials for High-Performance Supercapacitor and Dye-Sensitized Solar Cell.

Mesocrystalline Cu2O hollow nanocubes: synthesis and application in non-enzymatic amperometric detection of hydrogen peroxide and glucose