Room‐Temperature Electrochemical Conversion of Metal–Organic Frameworks into Porous Amorphous Metal Sulfides with Tailored Composition and Hydrogen Evolution Activity

Abstract

The conversion of metal-organic frameworks (MOFs) into inorganic nanomaterials is considered as an attractive means to produce highly efficient electrocatalysts for alternative-energy related applications. Yet, traditionally employed MOF-conversion conditions (e.g., pyrolysis) commonly involve multiple complex high-temperature reaction processes, which often make it challenging to control the composition, pore structure, and active-sites of the MOF-derived catalysts. Herein, a general, simple, room-temperature method is presented for a controlled electrochemical conversion of MOF (EC-MOF) films into porous, amorphous metal sulfides (a-MS x ). Detailed X-ray photoelectron spectroscopy analysis and control over independent EC-MOF parameters (e.g., scan-rate and potential window) enable to gain insights on the MOFconversion mechanisms, and in turn to fine-tune the porosity and composition of the obtained MS x . As a result, a highly active amorphous cobalt sulfide (a-CoS x ) electrocatalyst can be designed for hydrogen evolution reaction in neutral pH. Furthermore, the adjustable nature of the EC-MOF method allows to draw conclusions about the correlation between the concentration of catalytically active species (S 2 2sites) and the hydrogen evolution properties of the a-CoS x . Given the method's generality and the diversity of available MOF structures, EC-MOF provides a compelling platform for a rational design of a wide variety of active electrocatalytic materials.

Nitrogen Engineering on 3D Dandelion‐Flower‐Like CoS2 for High‐Performance Overall Water Splitting

“…The survey spectra of N‐CoS 2 shown in Figure S5 (Supporting Information) further indicates the presence of Co, S, and N. As shown in Figure a, the high‐resolution Co 2p spectra can be divided into Co 2p 3/2 and Co 2p 1/2 . The peaks located at 778.3 and 780.5 eV can be assigned to Co 0 (2p 3/2 ) and Co 2+ (2p 3/2 ), respectively . It can be seen clearly that the peak of Co 0 in N‐CoS 2 displays a positive shift of about 0.05 eV compared to that of CoS 2 .…”

Constructing Successive Active Sites for Metal‐free Electrocatalyst with Boosted Electrocatalytic Activities Toward Hydrogen Evolution and Oxygen Reduction Reactions

“…The micropores were beneficial for electrolyte diffusion as well as releasing of hydrogen molecular generated in hydrogen evolution reaction (HER) to reduce the charge/ mass transfer resistance resulting in high electrocatalytic activity, especially under high potential range. [17] Moreover, the EDS mappings depicted that N atoms were homogenously doped into carbon materials and quantitative analysis indicated that N doping amounts were 8.4 at%, 11.0 at%, 20.1 at% and 24.7 at% for PNC-1, PNC-2, PNC-3 and PNC-4, respectively. Continuously, the specific surface areas of different electrocatalysts were measured and shown in Figure S2a, in which the specific surface areas of PNC-0, PNC-1, PNC-2, PNC-3 and PNC-4 were 1156, 1075, 979, 850 and 1074 m 2 g À1 , respectively.…”

Recent Approaches to Design Electrocatalysts Based on Metal–Organic Frameworks and Their Derivatives

“…The better catalytic performance of porous CoP concave polyhedron should be associated with the porous structure, large surface area and highly conductive carbon network. Hod's group developed a facile experimental method to synthesize porous amorphous CoS x by the electrochemical conversion of ZIF‐67 MOF with various potential scan rates during the CV‐cycling . As shown in Figure e and f, the as‐prepared CoS x ‐(0.2–0.02)‐12, obtained after an electrochemical conversion of ZIF‐67 (12 growth cycles) with altered scan rates from 0.2 to 0.02 V s −1 , the overpotential of 168 mV at 10 mA cm −2 in neutral pH.…”

“…e) Schematic illustration showing the electrochemical conversion of ZIF‐67 to porous amorphous CoS x and f) the corresponding voltammetric curves and Tafel plots for the amorphous CoS x compared with other related catalysts. Reproduced with permission from reference . Copyright 2018, Wiley‐VCH.…”