No abstract

Development of a cost-effective and efficient electrocatalyst for the sluggish oxygen reduction reaction (ORR) is a crucial challenge for clean energy technologies. In this study, we have synthesized various Ni and Co oxide (NCO) nanomaterials via a facile coprecipitation, followed by the calcination method. The morphology of the formed NCO nanomaterials was controlled by varying the percentage of the Ni and Co precursors, leading to the formation of a template-free mesoporous spinel phase structure of Ni x ­Co3–x ­O4. It was found that the number of the octahedral site cations and the defect sites with lower oxygen in the spinel oxides can be tunable by taking appropriate ratios of the Ni and Co precursors. The optimized NCO nanomaterial exhibits superior electrocatalytic activity compared to the mono-metal oxides of NiO and Co3O4 with over 3 times higher current density and ∼0.250 V lower onset potential toward ORR in a 0.1 M KOH solution. Scanning electrochemical microscopy was utilized in mapping the activity of the catalyst and monitoring the ORR products, further confirming that a four-electron transfer pathway was facilitated by the NCO nanomaterial. Moreover, the developed mesoporous NCO nanomaterial exhibits a high methanol tolerance capability and long-term stability when compared to the commercial state-of-the-art Pt/C electrocatalyst. The improvement of the catalytic activity and stability of this advanced NCO nanomaterial toward ORR may be attributed to the facile accessible mesoporous structure, and the abundance of octahedral site cations and defective oxygen sites.

There is a lot of interest in understanding localized catalytic activities at the micro and nanoscale and designing robust catalysts for photoelectrochemical oxidation of water to address the pressing energy and environmental challenges. Here, we demonstrate that scanning photoelectrochemical microscopy (SPECM) can be effectively employed as a novel technique (i) to modify a photocatalyst surface with an electrocatalyst layer in a matrix fashion and (ii) to monitor its localized activity toward the photoelectrochemical (PEC) water oxidation reaction. The three-dimensional SPECM image clearly shows that the loading of the FeOOH electrocatalyst on the BiVO4 semiconductor surface strongly affects its local PEC reaction activity. The optimal photoelectrodeposition time of FeOOH on the BiVO4 photocatalyst was found to be ∼20 min when FeOOH was employed as the electrocatalyst. The electrocatalyst optimization process was conducted on a single photoanode electrode surface, making the optimization process efficient and reliable. The morphology of the formed photocatalyst/electrocatalyst hybrid, inclusive of its localized activity toward the water oxidation reaction, was simultaneously probed. A photoanode surface comprising CuWO4/BiVO4/FeOOH was further prepared in this study and investigated. It was found that the localized photoactivity truly reflects the activity of the local area, differs from region to region, and is contingent on the morphology of the surface. Moreover, the Pt UME is determined as an efficient probe to analyze the photoactivity of the PEC water splitting reaction. This work highlights the novel SPECM technique for enhancement and examination of the catalytic activity of the nanostructured materials.

The development of efficient electrocatalysts for the oxygen evolution reaction (OER) is an enduring challenge toward the commercialization of electrochemical technologies such as water electrolysis and solar to fuel production. Although noble metal based electrode materials (e.g., Pt, IrO2, and RuO2 etc.) are active catalysts for the OER, their cost-effectiveness, scarcity and long-term stability have hindered the development of electrochemical commercial applications. In addition, there is a great interest in the design of cost-effective and efficient catalysts for the oxygen reduction reaction (ORR) for the creation of clean energy technologies. In this presentation, we will report on the synthesis of one-dimensional Co3O4 nanorods, two-dimensional nanosheets, and three-dimensional nanocubes. The formed 1D, 2D, and 3D Co3O4 were systematically probed using a structure sensitive electrochemical OER, revealing that the 2D nanosheets exhibited higher catalytic activities in contrast to the 1D and 3D Co3O4, due to its high electrochemically active surface area and rich oxygen deficiencies. In addition, nanostructured nickel cobalt metal oxides with different composition were synthesized and studied for oxygen reduction. The effect of the composition, morphology, and active sites of the formed cobalt based nanomaterials on their catalytic activity will be discussed.

The rapid growth of pharmaceutical industries has led to new biomedical and environmental concerns. There is an urgent need for sensitive, portable and cost-effective sensors for the detection of pharmaceuticals to either track patient overdosing or to monitor the pollutants in the environment. Nanomaterial-based electrochemical sensing technologies can readily tackle the aforementioned problems, which spurred significant research interests recently [1-3]. In this presentation, the synthesis of nanoporous gold and graphene oxide-based nanomaterials for the electrochemical sensing of acetaminophen, naproxen and isoniazid is discussed. The design rationale and the performance of the proposed electrochemical sensors are highlighted. Specifically, the hierarchical nanoporous gold exhibited high sensitivity of 58.16 µAµM−1cm−2 and a low detection limit of 1.01 nM. In addition, it was found that the oxygen content of the graphene-based nanomaterials played a critical role in both sensing of naproxen and isoniazid. The proposed electrochemical sensors were further tested using real samples, which showed their promising applicability in biomedical and environmental applications. [1] J. van der Zalm, S. Chen, W. Huang, and A, Chen, J. Electrochem. Soc., 167 ,037532 (2020). [2] L. Qian, S. Durairaj, S. Prins, and A. Chen, Biosens. Bioelectron., 112836 (2020). [3] L. Qian, A.R. Thiruppathi, R. Elmahdy, J. van der Zalm, and A. Chen, Sensors., 20,1252 (2020).