Structural and Morphological Conversion between Two Co-Based MOFs for Enhanced Water Oxidation

Abstract

The rapid development of suitable and cheap water oxidation catalysts is of great significance in energy conversion and storage. In this context, herein we have synthesized two different types of metal−organic frameworks (MOFs, denoted as BMM-11 and BMM-12) constructed from the same metal salts (cobalt nitrate) and organic linkers (H 4 BPTC) at the similar solvothermal conditions. Interestingly, we learned that both crystalline materials can be conveniently converted into each other by a single-crystalto-single-crystal transformation method at their corresponding synthetic conditions. Meanwhile, we applied them directly as electrocatalysts into OER application where the pure BMM-11 and BMM-12 can achieve a stable current density of 10 mA cm −2 with an overpotential of 0.362 and 0.393 V, respectively, during which MOF degradation unexpectedly occurs. After electrolysis, the following microscopic, spectroscopic, as well as electrochemical measurements confirm that these initial MOF precursors are rapidly transformed into the mixed phases of CoO x H y species consisting of CoOOH and Co(OH) 2 , which are essentially active components for OER performance. Finally, we have also considered other strategies to improve MOF-derived composites in oxygen evolution activity, including bimetallic doping and physical grinding strategy. The approach described here can further be extended to other cobalt-based MOFs-derived electrocatalysts for water splitting.

Recent advancements in MOF‐ based catalysts for applications in electrochemical and photoelectrochemical water splitting: A review

“…105 Most recently, Zhong et al prepared two different types of MOFs (denoted as BMM-11 and BMM-12) by using metal salts of cobalt nitrate and organic linkers (H 4 BPTC) by the similar solvothermal process and they can be employed as direct electrocatalyst. 106 Integration of MOFs with functional materials in a controlled environment is resulting in the creation of new multifunctional composites, possessing characteristics superior to the individual components. Dai et al fabricated an electrocatalyst composite that is molybdenum polysulfide (MoS x ) anchored on Zr-based MOF (UiO-66-NH 2 ) modified by solvothermal synthesis process for HER application.…”

“…To control thickness and architecture of electrodes at molecular level, Cao et al used semi‐sacrificial template approach to fabricate self‐supporting electrode composed of ultrathin nanosheets of Ni‐rich Ni(Fe)‐MOF by using Ni‐Fe alloy foam as both metal source and substrate 105 . Most recently, Zhong et al prepared two different types of MOFs (denoted as BMM‐11 and BMM‐12) by using metal salts of cobalt nitrate and organic linkers (H 4 BPTC) by the similar solvothermal process and they can be employed as direct electrocatalyst 106 …”

“…Direct application of these MOFs for OER electrocatalysis can attain 10 mA/cm 2 of stable current density with an overpotential of 0.362 and 0.393 V, respectively. However, it was observed that during OER process, these pristine MOFs decompose to form catalytically active CoO x H y [Co(OH) 2 and CoOOH] nanosheets 106 …”

“…However, it was observed that during OER process, these pristine MOFs decompose to form catalytically active CoO x H y [Co(OH) 2 and CoOOH] nanosheets. 106…”

Recent Advances in Electrocatalysis of Oxygen Evolution Reaction using Noble‐Metal, Transition‐Metal, and Carbon‐Based Materials

“…Characterization techniques confirm the successful conversion of one form into another and the formation of Co (OH) 2 and CoOOH nanosheets during electrolysis. BMM‐11, directly used as a catalyst requires an overpotential 0.362 V for 10 mA/cm 2 current density along with a Tafel slope of 105 mV/dec while nickel doping results in a further reduction in Tafel slope [196] …”