The
search for a bifunctional electrocatalyst having water cleavage
promoting ability along with the operational stability to efficiently
generate oxygen and hydrogen could lead to robust systems for applications.
These fundamental ideas can be achieved by designing the morphology,
tuning the electronic structure, and using dopants in their higher
oxidation states. Herein, we have fabricated a binder-free FeO(OH)–CoCeV-layered
triple hydroxide (LTH) bifunctional catalyst by a two-step hydrothermal
method, in which the nanograin-shaped FeO(OH) coupled with CoCeV-LTH
nanoflakes provides more electrocatalytically active sites and enhances
the charge-transfer kinetics for hydrogen evolution reaction (HER)
and oxygen evolution reaction (OER). The composition-optimized electrocatalyst
(FeO(OH)–Co0.5Ce0.05V0.15-LTH)
acts as an efficient water cleavage composite by virtue of its favorable
oxidation states leading to cyclic redox couples, which yields an
overpotential of 53 mV for HER and 227 mV for OER to drive 10 mA/cm2 current density in 1 M KOH with a corresponding Tafel slope
of 70 mV/dec for HER and 52 mV/dec for OER. Furthermore, for the overall
water splitting reaction, the heterostructure FeO(OH)–Co0.5Ce0.05V0.15-LTH acts as a dual-functional
electrocatalyst, which requires a cell voltage of 1.52 V versus RHE
to drive 10 mA/cm2 current density.
One of the major limiting factorsf or efficient photoelectrochemical water oxidation is the fast recombination kinetics of photogenerated charge carriers. Herein,w ep ropose am odel system that utilizes ZnIn 2 S 4 and hierarchical VS 2 microflowersf or efficient charge separation through aZscheme pathway,w ithoutt he need for an electron mediator. An impressive 18-fold increase in photocurrent was observed for ZnIn 2 S 4 -VS 2 compared to ZnIn 2 S 4 alone. The charge-transfer dynamics in the composite were found to follow aZ -scheme pathway,w hich resulted in decreased charger ecombination and greater accumulation of the surface charge. Furthermore, slow kinetics of the surfacer eaction in the ZnIn 2 S 4 -VS 2 composite correlated to an increased surface-charge capacitance. This feature of the composite materialf acilitated partial storage of the photogenerated chargec arriers (e À /h + + )u nder illumination andd ark-current conditions, thus storing and utilizing solar energy more efficiently.
Rationally designing a noble metal-free electrocatalyst
for OER
and HER is pivotal for large-scale energy generation via water splitting.
A multimetallic electrocatalyst FeVO(OH)/Ni0.86Mo0.07W0.07(OH)2, aimed at tuning the electronic
structure, is fabricated and shows considerable improvement in the
water-splitting reaction kinetics, aided by low Tafel slope values
of 24 mV/dec for OER and 67 mV/dec for HER, respectively. By taking
advantage of (e̅–e̅) repulsions at the t2g level, we introduced high-valency Mo and W to provide a viable path
for π-electron donation from oxygen 2p orbitals to vacant Mo
and W orbitals for a dynamic electronic structure and an interfacial
synergistic effect, which optimized the bond lengths for reaction
intermediates to facilitate water splitting. The hybrid catalyst FeVO(OH)/NiMoW(OH)2 shows intrinsic activity and durability toward OER and HER
tested for 48 h at a current density of 20 mA/cm2 and a
cell voltage of 1.65 V @ 20 mA/cm2.
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