20 research outputs found
Electrocatalytic hydrogen evolution using amorphous tungsten phosphide nanoparticles
Amorphous tungsten phosphide (WP), which has been synthesized as colloidal nanoparticles with an average diameter of 3 nm, has been identified as a new electrocatalyst for the hydrogen-evolution reaction (HER) in acidic aqueous solutions. WP/Ti electrodes produced current densities of −10 mA cm^(−2) and −20 mA cm^(−2) at overpotentials of only −120 mV and −140 mV, respectively, in 0.50 M H_2SO_4(aq)
Amorphous Molybdenum Phosphide Nanoparticles for Electrocatalytic Hydrogen Evolution
Amorphous molybdenum phosphide (MoP) nanoparticles have been synthesized and characterized as electrocatalysts for the hydrogen-evolution reaction (HER) in 0.50 M H_2SO_4 (pH 0.3). Amorphous MoP nanoparticles (having diameters of 4.2 ± 0.5 nm) formed upon heating Mo(CO)6 and trioctylphosphine in squalane at 320 °C, and the nanoparticles remained amorphous after heating at 450 °C in H_2(5%)/Ar(95%) to remove the surface ligands. At mass loadings of 1 mg cm^–2, MoP/Ti electrodes exhibited overpotentials of −90 and −105 mV (−110 and −140 mV without iR correction) at current densities of −10 and −20 mA cm^–2, respectively. These HER overpotentials remained nearly constant over 500 cyclic voltammetric sweeps and 18 h of galvanostatic testing, indicating stability in acidic media under operating conditions. Amorphous MoP nanoparticles are therefore among the most active known molybdenum-based HER systems and are part of a growing family of active, acid-stable, non-noble-metal HER catalysts
A cyclic electrochemical strategy to produce acetylene from CO2, CH4, or alternative carbon sources
Electrochemical transformation of potent greenhouse gases such as CO2 and CH4 to produce useful carbon-based products is a highly desirable sustainability goal. However, selectivity challenges remain in aqueous electrochemical processes as selective CO2 reduction to desired products is difficult and electrochemical CH4 oxidation often proceeds at very low rates. The formation of C–C coupled products in these fields is particularly desirable as this provides a path for the production of high-value fuels and chemicals. We have developed a cyclic electrochemical strategy which can produce acetylene, a C–C coupled product, from such carbon sources and water, with favorable current density and selectivity. This strategy is exemplified with a lithium-mediated cycle: an active Li0 surface is electrochemically generated from LiOH, the newly formed Li0 reacts with a carbon source to form Li2C2, and Li2C2 is hydrolyzed to form acetylene and regenerate LiOH. We demonstrate this process primarily using CO2 gas, achieving a current efficiency of 15% to acetylene (which represents 82% of the maximum based on stoichiometric production of oxygenated byproducts, e.g. LiCO3 and/or Li2O), as verified by gas chromatography and Fourier transform infrared radiation studies. We also explore CH4, CO, and C as alternative precursors in the acetylene synthesis. Notably, the use of graphitic carbon at higher temperatures resulted in over 55% current efficiency to acetylene, with opportunity for further optimization. Importantly, this cycling method avoids the formation of common side products observed during aqueous electrochemical CO2 and CH4 redox reactions, such as H2, CO, HCO2−, or CO2. Theoretical considerations elucidate the feasibility and general applicability of this cycle and the process steps have been characterized with specific electrochemical and materials chemistry techniques. The continued development of this strategy may lead to a viable route for the sustainable production of C–C coupled carbon fuels and chemicals
Solution Synthesis of Metal Silicide Nanoparticles
Transition-metal silicides are part
of an important family of intermetallic compounds, but the high-temperature
reactions that are generally required to synthesize them preclude
the formation of colloidal nanoparticles. Here, we show that palladium,
copper, and nickel nanoparticles react with monophenylsilane in trioctylamine
and squalane at 375 °C to form colloidal Pd<sub>2</sub>Si, Cu<sub>3</sub>Si, and Ni<sub>2</sub>Si nanoparticles, respectively. These
metal silicide nanoparticles were screened as electrocatalysts for
the hydrogen evolution reaction, and Pd<sub>2</sub>Si and Ni<sub>2</sub>Si were identified as active catalysts that require overpotentials
of −192 and −243 mV, respectively, to produce cathodic
current densities of −10 mA cm<sup>–2</sup>
Nanostructured Co<sub>2</sub>P Electrocatalyst for the Hydrogen Evolution Reaction and Direct Comparison with Morphologically Equivalent CoP
Metal phosphides have emerged as
promising Earth-abundant alternatives
to platinum for catalyzing the hydrogen evolution reaction (HER) in
acidic aqueous solutions. Here, Co<sub>2</sub>P nanoparticles having
a hollow, multifaceted, crystalline morphology have been evaluated
as HER electrocatalysts at a mass loading of 1 mg cm<sup>–2</sup> on Ti foil substrates. The Co<sub>2</sub>P/Ti electrodes required
low overpotentials of −95 and −109 mV to produce operationally
relevant cathodic current densities of −10 and −20 mA
cm<sup>–2</sup>, respectively. These values establish Co<sub>2</sub>P nanoparticles as highly active Earth-abundant HER catalyst
materials. Importantly, the Co<sub>2</sub>P nanoparticles are morphologically
equivalent to previously reported CoP nanoparticle HER catalysts,
allowing a direct side-by-side evaluation of their HER activities.
Such comparisons of different metal phosphide HER catalysts with the
same constituent elements and morphologies are important for identifying
the key materials characteristics that lead to high activity