Ultrafine TaOx/CB Oxygen Reduction Electrocatalyst Operating in Both Acidic and Alkaline Media

The high activity of non-platinum electrocatalysts for oxygen reduction reaction (ORR) in alkaline media is necessary for applications in energy conversion devices such as fuel cells and metal-air batteries. Herein, we present the electrocatalytic activity of TaOx/carbon black (CB) nanoparticles for the ORR in an alkaline atmosphere as well as in an acidic electrolyte. Ultrafine TaOx nanoparticles 1–2 nm in size and uniformly dispersed on CB supports were prepared by potentiostatic electrodeposition in a nonaqueous electrolyte and subsequent annealing treatment in an H2 flow. The TaOx/CB nanoparticles largely catalyzed the ORR with an onset potential of 1.03 VRHE in an O2-saturated 0.1 M KOH solution comparable to that of a commercial Pt/CB catalyst. ORR activity was also observed in 0.1 M H2SO4 solution. According to the rotating ring disk electrode measurement results, the oxide nanoparticles partly produced H2O2 during the ORR in 0.1 M KOH, and the ORR process was dominated by both the two- and four-electron reductions of oxygen in a diffusion-limited potential region. The Tafel slope of −120 mV dec−1 in low and high current densities revealed the surface stability of the oxide nanoparticles during the ORR. Therefore, these results demonstrated that the TaOx/CB nanoparticles were electroactive for the ORR in both acidic and alkaline electrolytes.

Screening of bacterial isolates for phosphate solubilizing capability in a ferruginous ultisol in Benin City, Edo State, Nigeria

Phosphorus is a major growth-llimiting nutrient which plays important biochemical role in living system. It is widely distributed in minerals as phosphates. It reacts easily with Fe3+ in ferruginous ultisols and therefore not bioavailable for plant usage. Many bacteria have the ability to solubilize phosphate minerals and make it bioavailable to plants.Thus this research investigates the culturable bacterial composition of ferruginous ultisol, comparative to control soils as well as the phosphate solubilizing capabilities of the isolates for future use in soil improvements. Six soil samples of different ferruginous levels and a control were assayed for physicochemical parameters prior to the experiment. Culturable bacteria as well as the phosphate solubilizing bacteria (PSB) were assayed in Pikovskaya’s medium at 27oC with 7.5 pH for 7days. Six distinct isolates were observed which proved to be Proteus spp., Pseudomonas spp., Klebsiella spp., Salmonella spp., Bacillus spp. and Serratia spp. based on biochemical and morphological characteristics. Of these six isolates, three isolates(EMBF2-Klebsiella spp, BCAF1- Proteus spp and BCAC2- Bacillus spp) were identified to solubilize phosphate by releasing a considerable amount of phosphate (12.01-21.23 ppm) and lowering the pH of the media. The three isolates showed tolerance to acidic and alkaline media and also showed plant growth promoting capabilities by releasing indole acetic acid and siderophores. The result revealed that the three isolates had potential to chelate the ion bond in identified to solubilize phosphate by releasing a considerable amount of phosphate (12.01-21.23 ppm) and lowering the pH of the media. The three isolates showed tolerance to acidic and alkaline media and also showed plant growth promoting capabilities by releasing indole acetic acid and siderophores. The result revealed that the three isolates had potential to chelate the ion bond in Fe3+ in ferruginous ultisol by releasing low molecular weight organic acid, making phosphate to be bioavailable for plant usage. This will serve as biofertilizer in improving yield of crops in ferruginous ultisol and improve soil fertility.

Moving beyond bimetallic-alloy to single-atom dimer atomic-interface for all-pH hydrogen evolution

Single-atom-catalysts (SACs) afford a fascinating activity with respect to other nanomaterials for hydrogen evolution reaction (HER), yet the simplicity of single-atom center limits its further modification and utilization. Obtaining bimetallic single-atom-dimer (SAD) structures can reform the electronic structure of SACs with added atomic-level synergistic effect, further improving HER kinetics beyond SACs. However, the synthesis and identification of such SAD structure remains conceptually challenging. Herein, systematic first-principle screening reveals that the synergistic interaction at the NiCo-SAD atomic interface can upshift the d-band center, thereby, facilitate rapid water-dissociation and optimal proton adsorption, accelerating alkaline/acidic HER kinetics. Inspired by theoretical predictions, we develop a facile strategy to obtain NiCo-SAD on N-doped carbon (NiCo-SAD-NC) via in-situ trapping of metal ions followed by pyrolysis with precisely controlled N-moieties. X-ray absorption spectroscopy indicates the emergence of Ni-Co coordination at the atomic-level. The obtained NiCo-SAD-NC exhibits exceptional pH-universal HER-activity, demanding only 54.7 and 61 mV overpotentials at −10 mA cm−2 in acidic and alkaline media, respectively. This work provides a facile synthetic strategy for SAD catalysts and sheds light on the fundamentals of structure-activity relationships for future applications.