The pH Influence on the Water-Splitting Electrocatalytic Activity of Graphite Electrodes Modified with Symmetrically Substituted Metalloporphyrins

Abstract

Hydrogen, considered to be an alternative fuel to traditional fossil fuels, can be generated by splitting water molecules into hydrogen and oxygen via the use of electrical energy, in a process whose efficiency depends directly on the employed catalytic material. The current study takes part in the relentless search for suitable and low-cost catalysts relevant to the water-splitting field by investigating the electrocatalytic properties of the O2 and H2 evolution reactions (OER and HER) of two metalloporphyrins: Zn(II) 5,10,15,20-tetrakis(4-pyridyl)-porphyrin and Co(II) 5,10,15,20-tetrakis(3-hydroxyphenyl)-porphyrin. The TEM/STEM characterisation of the porphyrin samples obtained using different organic solvents revealed several types of self-assembled aggregates. The HER and OER experiments performed on porphyrin-modified graphite electrodes in media with different pH values revealed the most electrocatalytically active specimens. For the OER, this specimen was the electrode manufactured with one layer of Co-porphyrin applied from dimethylsulfoxide, exhibiting an overpotential of 0.51 V at i = 10 mA/cm2 and a Tafel slope of 0.27 V/dec. For the HER, it was the sample obtained by drop casting one layer of Zn-porphyrin from N,N-dimethylformamide that displayed a HER overpotential of 0.52 V at i = −10 mA/cm2 and a Tafel slope of 0.15 V/dec.

Free-Base Porphyrin Aggregates Combined with Nickel Phosphite for Enhanced Alkaline Hydrogen Evolution

“…At i = −10 mA/cm 2 , ηH2 = 0.43 V for GP4-NiPh-THF and 0.47 V for GNiPh-THF. A comparison between the results obtained on GP4-NiPh-THF in the two electrolyte solutions reveals that the increase in KOH concentration led to the improvement of the catalytic activity-a previously reported phenomenon [62,64]. The EASA value was estimated for both specimens, G P4-NiPh-THF and G NiPh-THF , following the procedure described in the Experimental Section and it was found to be 0.511 cm 2 and 0.427 cm 2 , respectively.…”

“…At i = −10 mA/cm 2 , ηH2 = 0.43 V for GP4-NiPh-THF and 0.47 V for GNiPh-THF. A comparison between the results obtained on GP4-NiPh-THF in the two electrolyte solutions reveals that the increase in KOH concentration led to the improvement of the catalytic activity-a previously reported phenomenon [62,64]. sample obtained by applying 1.5 mg NiPh from THF on the graphite support, designated GNiPh-THF.…”

“…Unless otherwise specified, the values of the current density (i) refer to the geometric current density. The hydrogen evolution overpotential was obtained with Equation ( 2), and the Tafel slope values were determined with Equation (3) [63,64].…”

New Hybrid Organic-Inorganic Structures for Water Splitting Electrocatalysts

“…The higher OER catalytic activity of the electrode modified with the P11 perovskite material, Carbon Black and Nafion is probably the outcome of structural and transport effects [48]. However, it should also be pointed out that the higher EASA value estimated for this sample indicates its surface is more discontinuous, probably due to features including edges and defects that generate more catalytically active centers [49]. Furthermore, it is sometimes the case that electrodes manufactured using compositions containing at least two materials benefit from improved charge transfer and adjusted electron density at the catalytic centers as a result of their interplay [50].…”

Nanographene‐Based Decoration as a Panchromatic Antenna for Metalloporphyrin Conjugates

“…For example, understanding and eventually fine-tuning charge carrier dynamics in molecular dyes is key to facilitating electron-transfer reactions in donoracceptor systems, where transferred electrons can subsequently trigger catalytic activity. [1][2][3] Typical examples of light induced catalysis based on these architectures are water splitting to produce hydrogen for fuel cells [4][5][6][7] and/or CO 2 reduction to achieve high added-value chemicals. [8,9] Within this context, harnessing parallel electronic decay pathways that detrimentally compete with the targeted photochemical reaction is crucial to improve photoconversion efficiency.…”