Carbon supported Pd–Sn nanoparticle eletrocatalysts for efficient borohydride electrooxidation

Abstract

<p>Carbon supported Pd-Sn nanoparticle electrocatalysts (Pd-Sn/C) are prepared via a facilely and environmental friendly method and successfully applied in BH4− electrooxidation. Transmission electron microscopy results and X-ray diffraction results show...</p>

Development of Bimetallic PdNi Electrocatalysts toward Mitigation of Catalyst Poisoning in Direct Borohydride Fuel Cells

“…The BOR activity is evaluated based on the values of the onset potential and the limiting currents, which is commonly used in the literature. ,, The onset potential of BOR is defined by the average potential at which the current is zero obtained during the forward scan and the backward scan . The observed BOR onset potential is a mixed potential that originates from the combination of several reactions such as hydrogen evolution reaction/hydrogen oxidation reaction (HER/HOR) and hydrolysis of BH 4 , leading to H 2 evolution and the electrochemical oxidation of the BOR-intermediate species.…”

“…Therefore, other benchmarking parameters of BOR along with the onset potential are used. In the literature, the current densities during the forward scan at E = 0.0 V vs RHE, 0.2 V vs RHE, and 0.5 V vs RHE along with onset potential have been used as the benchmarking parameters for BOR. ,,, The basic premise for choosing a benchmarking potential is identifying a region where BOR is fully developed (i.e., high BOR overpotential) with HOR current fully saturated (preferably >0.2 V vs RHE) and oxygen evolution reaction (OER) yet to set in (<1.23 V vs RHE). Herein, the current density at an anodic potential of 0.8 V vs RHE is chosen as the benchmarking potential.…”

“…10,62,63 The onset potential of BOR is defined by the average potential at which the current is zero obtained during the forward scan and the backward scan. 31 The observed BOR onset potential is a mixed potential that originates from the combination of several reactions such as hydrogen evolution reaction/hydrogen oxidation reaction (HER/HOR) and hydrolysis of BH 4 , leading to H 2 evolution and the electrochemical oxidation of the BOR-intermediate species. Hence, the onset potential is affected by the bubble formation, the adsorption of the BOR species, and the morphology of the electrocatalysts.…”

“…Coinage metals such as Au, Ag, and Cu bind with BH 4 – through molecular adsorption rather than dissociative adsorption. ,− These metals adsorb hydrogen weakly, resulting in a low hydrolysis rate. ,,, In fact, Au shows the highest selectivity toward BOR over hydrolysis, but it exhibits very low activity because of the less-favorable adsorption energy of BH 4 – vis-à-vis the water molecule. , Furthermore, these coinage metals show low electrocatalytic activity toward the BOR owing to their inability to activate B–H bond breaking. ,, Despite not producing all the eight electrons during BH 4 – oxidation, Pd electrocatalysts enable large current densities with high Faradaic efficiencies. ,,− However, full utilization of the active sites is not possible because of the high rate of the parasitic hydrolysis (hydrogen evolution) reaction, which blocks access to the active sites. Alloying or mixing d-group metals (e.g., Ir, Sn, Ni, Ni-Cu, , or Ni-Co) with Pd metal has resulted in an increase in the activity and selectivity of BOR. Among the earth-abundant metals, Ni favors a strong dissociative adsorption of BH 4 – . ,, However, the dissociation energy of BH 4 – on Ni is higher (more positive) than that of Pd, which leads to a lower hydrolysis rate and consequently to a lower probability of active-site poisoning on Ni surfaces .…”

“…2,19,28−30 However, full utilization of the active sites is not possible because of the high rate of the parasitic hydrolysis (hydrogen evolution) reaction, which blocks access to the active sites. Alloying or mixing d-group metals (e.g., Ir, 13 Sn, 31 Ni, 32 Ni-Cu, 1,33 or Ni-Co 34 ) with Pd metal has resulted in an increase in the activity and selectivity of BOR. Among the earth-abundant metals, Ni favors a strong dissociative adsorption of BH 4 − .…”