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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. [ABSTRACT FROM AUTHOR]

The hydrogen evolution reaction (HER) at Pt-cathodes of microbial electrolysis cells (MEC) has been associated with overpotentials of several hundred millivolts. The high overpotentials challenge the sustainability of an MEC. This paper shows that the HER overpotential at MEC relevant pH values is reduced if buffer is present At 15 A/m2 and 50 mM buffer, the lowest overpotential for phosphate was -0.05 Vat pH 6.2, for ammonia was -0.05 V at pH 9.0, for carbonate was -0.09 V at pH 9.3, for Tris(hydroxymathyl)aminomathane was -0.07 V at pH 7.8, and for N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid was -0.08 V at pH 7.2. It was shown that the effect of buffer on the overpotantial is strongly pH dependent Furthermore, experimental data and a mass transport equation showed that by increasing the buffer concentration or linear flow speed (i.e., pump speed), or decreasing the currant density (i) the overpotential reduces and (iii) the minimum overpotential is reached at a pH that approaches the buffer dissociation constant (ρKa). Thus, to reduce the HER overpotential of an MEC, buffer (i.e., ρKa, buffer concentration, linear flow speed, and currant density must be well balanced with the expected operational pH. [ABSTRACT FROM AUTHOR]