Self-Assembly of Ir-Based Nanosheets with Ordered Interlayer Space for Enhanced Electrocatalytic Water Oxidation

Abstract

Iridium (Ir)-based electrocatalysts are widely explored as benchmarks for acidic oxygen evolution reactions (OERs). However, further enhancing their catalytic activity remains challenging due to the difficulty in identifying active species and unfavorable architectures. In this work, we synthesized ultrathin Ir-IrO x /C nanosheets with ordered interlayer space for enhanced OER by a nanoconfined self-assembly strategy, employing block copolymer formed stable end-merged lamellar micelles. The interlayer distance of the prepared Ir-IrO x /C nanosheets was well controlled at ∼20 nm and Ir-IrO x nanoparticles (∼2 nm) were uniformly distributed within the nanosheets. Importantly, the fabricated Ir-IrO x /C electrocatalysts display one of the lowest overpotential (η) of 198 mV at 10 mA cm −2 geo during OER in an acid medium, benefiting from their features of mixed-valence states, rich electrophilic oxygen species (O (II-δ)− ), and favorable mesostructured architectures. Both experimental and computational results reveal that the mixed valence and O (II-δ)− moieties of the 2D mesoporous Ir-IrO x /C catalysts with a shortened Ir−O (II-δ)− bond (1.91 Å) is the key active species for the enhancement of OER by balancing the adsorption free energy of oxygen-containing intermediates. This strategy thus opens an avenue for designing high performance 2D ordered mesoporous electrocatalysts through a nanoconfined selfassembly strategy for water oxidation and beyond.

Polarization Engineering of Covalent Triazine Frameworks for Highly Efficient Photosynthesis of Hydrogen Peroxide from Molecular Oxygen and Water

“…[53] When there was no O 2 in the reaction environment, a small quantity of H 2 O 2 was detected after 10 min of photoreaction, which increased with reaction time (Figure S27, Supporting Information), suggesting that the O 2 produced from water oxidation reaction is subsequently consumed by the 2e − ORR process to generate H 2 O 2 , leading to boosted overall reaction kinetics. [16,54,55] To further confirm the contributions of incorporation of urea and thiourea moieties, the dipoles moment of three composition fragments (highlighted by blue, yellow, and orange, Figure 5a and Figure S28a,c, Supporting Information) were investigated, exhibiting an increasing trend from ≈1.28 Å (Dc-CTF) to ≈2.16 Å (Bpu-CTF) and ≈2.23 Å (Bpt-CTF). The high dipole moment (polarization) contributes to a strong built-in electric field, which can promote in-plane charge transfer.…”

“…[ 53 ] When there was no O 2 in the reaction environment, a small quantity of H 2 O 2 was detected after 10 min of photoreaction, which increased with reaction time (Figure S27, Supporting Information), suggesting that the O 2 produced from water oxidation reaction is subsequently consumed by the 2e − ORR process to generate H 2 O 2 , leading to boosted overall reaction kinetics. [ 16,54,55 ]…”

Iridium nanohollows with porous walls for acidic water splitting

“…Iridium is the only element that catalyzes the OER in strong acid with satisfactory activity and stability. [11][12][13][14][15][16] However, the scarcity of Ir has posed severe limitations to the widespread application of PEMWEs in terms of both cost and supply constraints, which has motivated considerable research efforts to upgrade Ir-based OER electrocatalysts. [17][18][19][20][21][22] A widely-adopted upgrading strategy is to alloy Ir with other elements.…”

Sulfur‐Doped Hydrogen‐Bonded Organic Framework for Improved Oxygen Evolution Reaction

“…Whereas, the oxygen evolution reaction (OER), as the half-cell reaction, limits the entire energy conversion efficiency of electrochemical water splitting reaction due to its sluggish kinetics. [1][2][3][4][5][6] Developments of efficient electrocatalysts to accelerate the OER reaction are thus required. At present, iridium (Ir) and ruthenium (Ru) based noble-metal materials are utilized as OER catalysts with the benchmark performance, but their scarce and expensive nature seriously hinders their widespread utilization.…”

“…The concerns of the growing global warming and energy consumption have boosted the developments in electrochemical water splitting technologies to create the clean H 2 . Whereas, the oxygen evolution reaction (OER), as the half‐cell reaction, limits the entire energy conversion efficiency of electrochemical water splitting reaction due to its sluggish kinetics [1–6] . Developments of efficient electrocatalysts to accelerate the OER reaction are thus required.…”