Pt Nanoparticle Anchored Molecular Self-Assemblies of DNA: An Extremely Stable and Efficient HER Electrocatalyst with Ultralow Pt Content

An efficient electrocatalytic hydrogen evolution reaction (HER) with ultralow loading of Pt has been under intense investigation to make the state-of-the-art Pt economically affordable for water electrolyzers. Here, colloidally synthesized Pt nanoparticles of average size 3.5 ± 0.3 nm were successfully anchored on molecular self-assemblies of DNA. The synthesized Pt@DNA colloidal solution was directly assessed for the electrochemical hydrogen evolution reaction (HER) in 0.5 M H₂SO₄ with a loading of 5 μL of Pt@DNA colloidal solution that corresponds to a Pt equivalent of 15 μg/cm². The excellent adhesion of DNA onto GC and FTO substrate electrodes, the conductivity of DNA, and its stability upon potentiostatic electrolysis and accelerated degradation have made the synthesized, stable Pt@DNA colloidal solution an advanced HER electrocatalyst. The Pt@DNA–GC interface without binder required overpotentials of −0.026 and −0.045 V for current densities of 10 and 20 mA/cm², respectively. The potentiostatic electrolysis and accelerated degradation tests did not affect the electrocatalytic activity, and the observed increase in overpotential was highly negligible. The extreme stability of the Pt@DNA–GC interface was witnessed during an aging study carried out by keeping the working electrode in the electrolyte solution for more than 10 days and acquiring linear sweep voltammograms (LSVs) at intervals of 24 h. Under the same experimental conditions, the commercial Pt/C 10 wt % catalyst with Nafion binder had failed to compete with our colloidal Pt@DNA. These findings certainly indicate the advantageous use of electrocatalyst-loaded DNA molecular self-assemblies for the HER which has never been observed before

Study of the Oxygen Evolution Reaction Catalytic Behavior of Co_<i>x</i>Ni_1–<i>x</i>Fe₂O₄ in Alkaline Medium

Catalysts for the oxygen evolution reaction (OER) play an important role in the conversion of solar energy to fuel of earth-abundant water into H₂ and O₂ through splitting/electrolysis. Heterogeneous electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) exhibit catalytic activity that depends on the electronic properties, oxidation states, and local surface structure. Spinel ferrites (MFe₂O₄; M = Ni and Co) based materials have been attractive for the catalytic water oxidation due to their well-known stability in alkaline medium, easy synthesis, existence of metal cations with various oxidation states, low cost, and tunable properties by the desired metal substitution. To understand the better catalytic activity of MFe₂O₄ in detail the role of Ni and Co was studied through M_<i>x</i>Ni_1–<i>x</i>Fe₂O₄ (M = Co; 0 < <i>x</i> < 1), which was prepared by the sol–gel method. The results showed that bare NiFe₂O₄ has better catalytic activity (η = 381 mV at 10 mA cm^–2 and Tafel slope of 46.4 mV dec^–1) compared to Co-containing M_<i>x</i>Ni_1–<i>x</i>Fe₂O₄ (η = 450–470 mV at 10 mA cm^–2 and Tafel slope of 50–73 mV dec^–1) in alkaline medium, and the substitution of Co is found to suppress the catalytic activity of NiFe₂O₄. The degradation of catalytic activity with an increase in Co content was accounted for in further detailed investigations

Microwave-Assisted Template-Free Synthesis of Ni₃(BO₃)₂(NOB) Hierarchical Nanoflowers for Electrocatalytic Oxygen Evolution

The construction of cost-effective, efficient, and sustainable catalytic systems for electrocatalytic hydrogen generation by water splitting is extremely important for future fuels globally. Herein, we have prepared nickel orthoborate (NOB) via simultaneous oxidation and reduction of nickel precursors and studied their role in oxygen evolution reaction (OER) for water electrolysis. In addition, the specific role of microwave irradiation and conventional stirring in the formation of NOB was also investigated with comparative assessment of their catalytic ability in electrochemical water splitting. It was found that NOB nanoflowers prepared via microwave irradiation exhibited better OER electrocatalyst than the ones prepared by conventional heating. Interestingly, the NOB nanoflowers outperformed the commercial NiO nanopowder under the identical experimental conditions in catalyzing OER. Morphological hierarchy and high Brunauer–Emmett–Teller specific surface area were attributed for their enhanced OER activity. A long run of 6 h chronopotentiometry analysis showed a negligible degradation in activity signified the high stability and endurance of NOB nanoflowers. The numbers of merits from the electrochemical characterizations revealed that NOB nanoflowers could be an alternate, efficient, and abundant OER electrocatalyst for bulk water electrolysis

Self-Assembled Molecular Hybrids of CoS-DNA for Enhanced Water Oxidation with Low Cobalt Content

Water oxidation in alkaline medium was efficiently catalyzed by the self-assembled molecular hybrids of CoS-DNA that had 20 times lower Co loading than the commonly used loading. The morphological outcome was directed by varying the molar ratio of metal precursor Co­(Ac)₂ and DNA and three different sets of CoS-DNA molecular hybrids, viz. CoS-DNA(0.036), CoS-DNA(0.06), and CoS-DNA(0.084) were prepared. These morphologically distinct hybrids had shown similar electrocatalytic behavior, because of the fact that they all contained the same cobalt content. The CoS-DNA(0.036), CoS-DNA(0.06), and CoS-DNA(0.084) required very low overpotentials of 350, 364, and 373 mV at a current density of 10 mA cm^–2 (1 M KOH), respectively. The advantages of lower overpotential, lower Tafel slope (42.7 mV dec^–1), high Faradaic efficiency (90.28%), high stability and reproducibility after all, with a lower cobalt loading, have certainly shown the worth of these molecular hybrids in large-scale water oxidation. Moreover, since DNA itself a good binder, CoS-DNA molecular hybrids were directly casted on substrate electrodes and used after drying. It also showed minimum intrinsic resistance as DNA is a good ionic and electronic conductor. Besides, the present method may also be extended for the preparation of other active electrocatalysts for water splitting