Large-scale amorphous metal oxide films deposited on arbitrary substrates via redox interaction exhibit greater efficiency and durability in electrocatalytic oxygen evolution than benchmark materials.
Graphene oxide (GO) sheets have been used to construct various bulk forms of GO and graphene-based materials through solution-based processing techniques. Here, we report a highly cohesive dough state of GO with tens of weight percent loading in water without binder-like additives. The dough state can be diluted to obtain gels or dispersions, and dried to yield hard solids. It can be kneaded without leaving stains, readily reshaped, connected, and further processed to make bulk GO and graphene materials of arbitrary form factors and tunable microstructures. The doughs can be transformed to dense glassy solids of GO or graphene without long-range stacking order of the sheets, which exhibit isotropic and much enhanced mechanical properties due to hindered sliding between the sheets. GO dough is also found to be a good support material for electrocatalysts as it helps to form compliant interface to access the active particles.
Demand for rapid and massive-scale exfoliation of bulky graphite remains high in graphene commercialization and property manipulation. We report a procedure utilizing “preformed acidic oxidizing medium (PAOM)” as a modified version of the Hummers’ method for fast and reliable synthesis of graphene oxide. Pre-mixing of KMnO4 and concentrated H2SO4 prior to the addition of graphite flakes enables the formation of effectively and efficiently oxidized graphene oxide (EEGO) featured by its high yields and suspension homogeneity. PAOM expedites diffusion of the Mn-oxidants into the graphite galleries, resulting in the rapid graphite oxidation, capable of oxidizing bulky graphite flakes (~0.8 mm in diameter) that can not be realized by the Hummers’ method. In the scale-up tests, ten-time amount of graphite can be completely exfoliated by PAOM without need of extended reaction time. The remarkable suspension homogeneity of EEGO can be exploited to deposit ultra-flat coating for wafer-scale nanopatterning. We successfully fabricated GO optical gratings with well-defined periodicity (300 nm) and uniform thickness (variation <7 nm). The combination of the facile and potent PAOM approach with the wafer-scale patterning technique may realize the goal for massive throughput graphene nanoelectronics.
splitting, low-cost and facile fabrication of electrocatalysts, active for oxygen evolution reaction (OER) without involving precious metals (e.g., Ru and Ir), is therefore the central interests. [8,9] General approaches and knowledge capable of enhancing atom-efficiency in OER are also essential to conserve all the elements used in electrocatalysts regardless the individual nature abundance.As compared to colloidal electrocatalysts, scalable thin film electrocatalysts have been recognized by rapid mass transfer and robust adhesion with electrodes against peeling of electrocatalytic materials during oxygen bubbling, essential to achieve durable water splitting, high power output, and commercial demand of coating on various substrates. [10] The previous OER studies have concentrated on exploring continuous, void-free thin films of Ni, Co, Fe, and Mn oxides in alkaline conditions, [5,[10][11][12][13][14][15][16][17][18][19] revealing the important electrocatalytic influence regarding crystal structures, synergistic behaviors between elements, catalytic roles of active species, alternation of orbitals and electron transfer, and deposition methodologies. As electrocatalytic OER requires electricity (anodic current) and mass transport of reactants (water/OH − ) and product (O 2 ) at catalytic sites to proceed, this so-called "triple-phase boundary region," [20] usually at the heterojunction edges, is anticipated to deliver the best OER activities. By dividing a continuous thin film into fractured, discontinuous pieces (as a concept of "thin film imperfection"), the additionally exposed edge sites can thus greatly improve OER performance and atom efficiency. Recent designs of single atom catalysts may further support this idea. [21,22] In fact, strong edge effects on improving hydrogen evolution reaction (the other half reaction in water splitting) have been well recognized. [23,24] However, this concept of edge exposure in thin film has received much less attentions possibly due to the investigation complexity and coverage uncertainty of discontinuous deposition. With the example of photolithography-patterned electrocatalysts toward improved OER, [25] correlation of OER performance to systematic edge exposure normalizing to unit area is then becoming the most desired information. Recent study on the edge-site atom population of discrete, atom-scale deposition of iron oxides shows a proportional relationship to OER activities. [26] Despite the emerging of edge-dependent OER, reliable deposition over large area with versatile coverage/continuity to achieve Thin film electrocatalysts allow strong binding and intimate electrical contact with electrodes, rapid mass transfer during reaction, and are generally more durable than powder electrocatalysts, which is particularly beneficial for gas evolution reactions. In this work, using cobalt manganese oxyhydroxide, an oxygen evolution reaction (OER) electrocatalyst that can be grown directly on various electrodes as a model system, it is demonstrated that breaking a continuous...
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