Design and Synthesis of Lead(II)-Based Electrocatalysts for Oxygen Evolution Reaction.

A well-organized worldwide effort in providing remedies to sustainable clean energy generation and storage has focused on the strategic design and development of stable and efficient earth-abundant metal (Fe, Co, Ni, Pb, etc.)-based electrocatalysts for the oxygen evolution reaction (OER). Unfortunately, examples of Pb-based catalysts for such a process are rare. In this work, based on the dual-linker strategy, we have designed and synthesized two new two-dimensional (2D) coordination polymers of Pb with the hcb topology, [Pb2(tpbn)(adc)2]·4H2O·0.5CH3OH}n (CP1) and {[Pb2(tpbn)(fum)2]·7H2O}n (CP2), in excellent yields by the room-temperature self-assembly of Pb(OAc)2, tpbn, and H2adc or H2fum (where tpbn = N,N',N‴,N‴'-tetrakis-(2-pyridylmethyl)-1,4-diaminobutane, H2adc = acetylene dicarboxylic acid, and H2fum = fumaric acid). In addition to determining their X-ray single crystal structures, the phase purity and thermal stability were established by powder X-ray diffraction and thermogravimetric analysis, respectively. Furthermore, these were also characterized by the microscopic techniques (SEM/EDX and TEM/HRTEM). For their conductive and highly stable nature in alkaline medium, both CP1 and CP2 were tested for their suitability in the OER process. Interestingly, with a subtle change from adc in CP1 to fumarate in CP2 as the dicarboxylate linker, the latter performed much better than the former and displayed an excellent electrochemical stability in basic medium. Remarkably, CP2 has one of the lowest Tafel values (35 mV dec-1) and a low overpotential value (140 mV vs RHE) in 0.5 M KOH compared to those reported for any materials. Such a comparative study with CP1 and CP2, which are the simplest CPs and made with green-chemistry protocols for an easy making in large quantities, provides an outlook to developing the next-generation Pb-based electrocatalysts.

Spherical Ni/NiO nanoparticles decorated on nanoporous carbon (NNC) as an active electrode material for urea and water oxidation reactions.

Herein, we report a chemical method for scalable synthesis of spherical Ni/NiO nanoparticle-decorated nanoporous carbon (NNC) based electrocatalytic system using a simple and easy chemical method with ultra-high activity towards urea electrooxidation. Morphological analysis by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) confirms the formation of Ni/NiO NPs on highly nanoporous carbon with an average size of ∼50 nm. X-ray diffraction (XRD) confirms NNC with a face-centred cubic (FCC) crystal structure. Ni/NiO NPs intercalated with nanoporous carbon exhibited the best electrocatalytic performance towards urea oxidation with an ultra-low onset potential of ∼0.33 V vs. SCE, and faster electrokinetic mechanism confirmed from Tafel slope (∼45 mV dec-1), EIS Rct (∼6.98 Ω), and long term durability for 7 h at 10 mA cm-2 with high CO poisoning tolerance. This work affords noble metal-free electrocatalysts for novel appliances and remarkable potential for urea determination, hydrogen generation, real-time water remediation, and energy conversion.

Recent Progress on Carbon Quantum Dots Based Photocatalysis.

As a novel carbon allotrope, carbon quantum dots (CQDs) have been investigated in various fields, including photocatalysis, bioimaging, optoelectronics, energy and photovoltaic devices, biosensing, and drug delivery owing to their unique optical and electronic properties. In particular, CQDs' excellent sunlight harvesting ability, tunable photoluminescence (PL), up-conversion photoluminescence (UCPL), and efficient photo-excited electron transfer have enabled their applications in photocatalysis. This work focuses on the recent progress on CQDs-related materials' synthesis, properties, and applications in photocatalysis.

Enhanced Overall Water-Splitting Performance: Oleylamine-Functionalized GO/Cu2ZnSnS4 Composite as a Nobel Metal-Free and NonPrecious Electrocatalyst.

Using emergent highly proficient and inexpensive non-noble metal-based bifunctional electrocatalysts to overall water splitting reaction is a pleasingly optional approach to resolve greenhouse gases and energy anxiety. In this work, oleylamine-functionalized graphene oxide/Cu2ZnSnS4 composite (OAm-GO/CZTS) is prepared and investigated as a higher bifunctional electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The OAm-GO/CZTS shows brilliant electrocatalytic performance and durability toward H2 and O2 in both acidic and basic media, with overpotentials of 47 mV for HER and 1.36 V for OER at a current density of 10 mA cm-2 and Tafel slopes of 64 and 91 mV dec-1, respectively, which are extremely higher to those of transition metal chalcogenide and as good as of commercial precious-metal catalysts.

Enhanced oxygen evolution reaction on amine functionalized graphene oxide in alkaline medium.

Development of highly efficient oxygen evolution reaction (OER) electrocatalysts is a critical challenge in the cost-effective generation of clean fuels. Here, a metal-free tyramine functionalized graphene oxide (T-GO) electrocatalyst is proposed to use in alkaline electrolytes for enhanced OER. Moreover, the T-GO and GO nanomaterials are well characterized by SEM, XRD, FTIR, XPS and Raman spectroscopy. T-GO exhibits an electrocatalytic OER with a current density of 2 mA cm-2 at a low onset potential of ∼1.39 V and a small Tafel slope of about 69 mV dec-1 and GO exhibits an onset potential of 1.51 V and Tafel slope of about 92 mV dec-1. Additionally, the current stability and RRDE based diffusion controlled response of the T-GO electrocatalyst are outstanding compared to GO. This study establishes metal free T-GO as an efficient electrocatalyst for the OER and used for cathodic production of hydrogen as a counter reaction in the field of water splitting.

Graphene oxide-based electrochemical activation of ethionamide towards enhanced biological activity.

The electrochemical behavior of ethionamide (ETO) was investigated on GO (∼500 nm) using the linear sweep voltammetric (LSV) technique at the sweep rate of 10 mV s-1 in 1 M PBS buffer solution, and the characteristic anodic signal was examined at 0.240 V over the potential range of -0.4 to 1 V vs. SCE. However, linearity was observed with the increase in scan rate (2-300 mV s-1) and concentration of ETO (1 µM to 100 mM), suggesting that the process involved diffusion-controlled electron transfer. The results also exhibited excellent current and potential stability, limit of detection (LOD 1.33) and limit of quantification (LOQ 4.4) at optimized experimental conditions. This electrochemical oxidation method was successfully applied in the complete oxidation of ETO to its oxidized form, which was further confirmed by high resolution mass spectroscopy (HRMS) and Fourier transform infrared (FTIR) spectroscopic measurements. Interestingly, the comparative biological evaluation of ETO and ETO-O (oxidised form) showed good enhancement in the activity of oxidised ETO against some Gram-negative pathogens, such as E. aerogenes, S. abony, S. boydii, and E. coli.

CZTS Decorated on Graphene Oxide as an Efficient Electrocatalyst for High-Performance Hydrogen Evolution Reaction.

Cu2ZnSnS4 (CZTS) was synthesized by the sonochemical method using 2-methoxyethanol as the solvent and subsequently decorated onto graphene oxide (GO synthesized by the modified Hummers' method) using two different approaches such as in situ growth and ex situ synthesis followed by deposition. Preliminary characterizations indicated that the synthesized CZTS belongs to the kesterite structure with a sphere-like morphology. The in situ-synthesized CZTS/GO (I-CZTS/GO) composite is used as an efficient electrocatalyst for hydrogen evolution reaction (HER) which revealed superior electrocatalytic activity with a reduced overpotential (39.3 mV at 2 mA cm-2), Tafel slope (70 mV dec-1), a larger exchange current density of 908 mA cm-2, and charge transfer resistance (5 Ω), significantly different from pure CZTS. Besides, the I-CZTS/GO composite exhibits highest HER performance with high current stability of which shows no noticeable degradation after i-t amperometry. The catalytic activity demonstrates that the I-CZTS/GO composite could be a promising electrocatalyst in hydrogen production from their cooperative interactions.

Enhanced electrocatalytic hydrogen generation from water via cobalt-doped Cu2ZnSnS4 nanoparticles.

Herein, we adopted a novel noble metal-free Co-doped CZTS-based electrocatalyst for the hydrogen evolution reaction (HER), which was fabricated using a facile, effective, and scalable strategy by employing a sonochemical method. The optimized Co-doped CZTS electrocatalyst shows a superior HER performance with a small overpotential of 200 and 298 mV at 2 and 10 mA-1, respectively, and Tafel slope of 73 mV dec-1, and also exhibits excellent stability up to 700 cycles with negligible loss of the cathodic current. The ease of synthesis and high activity of the Co-doped CZTS-based cost-effective catalytic system appear to be promising for HER catalysis.