An Alkaline-Stable, Metal Hydroxide Mimicking Metal–Organic Framework for Efficient Electrocatalytic Oxygen Evolution

Abstract

Postsynthetic ion exchange of [Co2(μ-Cl)2(btta)] (MAF-X27-Cl, H2bbta =1H,5H-benzo(1,2-d:4,5-d')bistriazole) possessing open metal sites on its pore surface yields a material [Co2(μ-OH)2(bbta)] (MAF-X27-OH) functionalized by both open metal sites and hydroxide ligands, giving drastically improved electrocatalytic activities for the oxygen evolution reaction (an overpotential of 292 mV at 10.0 mA cm(-2) in 1.0 M KOH solution). Isotope tracing experiments further confirm that the hydroxide ligands are involved in the OER process to provide a low-energy intraframework coupling pathway.

Electrochemical Water Oxidation Catalyzed by an In Situ Generated α‐Co(OH)2 Film on Zeolite‐Y Surface

“…[31] Herein, we report an in situ generated zeolite-Y-supported a-Co(OH) 2 film as aC o-OECw ith enormous stability and good efficiency.W er eport av ery simple but unique technique to generate at hin-film of a-Co(OH) 2 of a-Co(OH) 2 on the surface of zeolite-Y also remains the same. Moreover,t he efficiency of this heterogeneous electrocatalytic system is highert han for the existing, previously reported, aCo(OH) 2 -based electrocatalysts operating at alkalinep H. [29,30,32] Results and Discussion Figure 1c ompares 6 (Figure 1) matches well with that of previously reported Co II -exchanged zeolite-Y. [33] As shown in Figure 1, the relative intensities of the diffraction peaks at 10.1 and 11.88 are found to be reversed in Y-Co II (H 2 O) 6 .T his could be attributed to ac hange in the structure factor of zeolite-Y upon exchange with ar elatively heavier ion (Co II ), as has been reportedf or Cs I -exchanged zeolite-Y.…”

“…The zeolite support probably prevented the catalyst particles from agglomeration, thereby enhancing the activity as well as the long-term durability.W eh ave performed detailed electrochemical experiments to determine the oxygenevolution kinetics andf ound aT afel slope as low as 59 mV decade À1 at an overpotential of 329 mV with aT OF of 0.35 mol O 2 mol Co À1 s À1 at 1mAcm À2 in alkalinem edium (pH 13). Thus, the efficiency of this heterogeneous electrocatalytic system is superior to the existing a-Co(OH) 2 -based oxygenevolution electrocatalysts operating at alkalinep H. [29,30,32] Experimental Section Materials Sodium zeolite-Y was procured from Sigma-Aldrich (Molecular sieves, CAS No. 334 448, MDL No.…”

“…The calculated TOF is the lower limit of each actives ite because not all Co-atoms/ions present in the catalystt ake parti ne lectrocatalysis. The turnover number (TON) at ap articularo verpotential (and hence at ap articular current density) can thenb ereadily calculated by considering that each catalytic turnover requires the transfer of four electrons (4 e À /4 H + process) according to Equation (2): [32] j ¼ 4FÂ TON ð2Þ in which j is the current density at ag iven overpotential and F is the Faraday constant. Dividing the TON by the number of active Co centers thus gives the TOF.T he calculatedl ower limit of the TOF for Y-a-Co(OH) 2 in 0.1 m KOH is 0.87 mol O 2 (mol Co) À1 s À1 at h = 360 mV (starting point of the Ta fel plot) and 0.02 at h = 260 mV (end point of the Ta fel plot).…”

“…The value is even higher than for other Co(OH) 2 based electrocatalysts reported in recent times (SectionS7i n the SupportingI nformation). [29,30,32] Another striking feature of this catalyst is its stability under operating conditions. For this, an accelerated durability test was performed by recording 2000 cycles of CV scans.…”

Recent Progress in Metal‐Organic Frameworks for Applications in Electrocatalytic and Photocatalytic Water Splitting

“…As such, one of the most challenging and rewarding endeavors in this field is to synthesize porous MOFs with good charge mobility and conductivity. Recently, the development of new type MOFs with enhanced intrinsic conductivity has attracted increasing attention 125, 126, 127. In 2009, Takaishi et al reported one of the first conductive MOFs, Cu[Cu(pdt) 2 ] (pdt = 2,3‐pyrazinedithiolate), and its electrical conductivity was 6 × 10 −4 S cm −1 at 300 K 128.…”