Prussian blue analogues are one of the most promising
examples
of water oxidation catalysts presenting great performance, activity,
and stability under mild conditions. Herein, we report an alternative
methodology to synthesize the Prussian blue, obtaining a catalyst
with vacancies created by an electrochemical method. This catalyst
showed an outstanding activity, with an onset overpotential of 361
mV. Using pyridine as a molecular probe, we identified the presence
of vacant Fe2+ sites, and the quantification of these sites
allowed us to estimate a TOF number of 0.2170 s–1 for the water oxidation reaction. These results indicate that defect
engineering is a versatile strategy to boost the catalytic activity
in Prussian blue analogues by increasing the number of active sites.
Non-stoichiometric hydroxyapatite (HAp) presents an additional phase in its structure due to calcium or phosphorus excess, which can influence the material’s mechanical properties, as well as its bioactivity and biodegradability. While stoichiometric HAp, with calcium to phosphorus ratio (Ca/P) of 1.67, has been widely investigated, only a few studies have reported the synthesis of HAp with higher Ca/P ratio. In this work, non-stoichiometric HAp nanoparticles were synthesized using chemical precipitation method followed by a calcination protocol. In order to achieve better process control with chemical precipitation, starch, a natural additive, was applied. Three types of starch were selected for comparison: nonionic starch (NS), soluble starch (SS), and cationic starch (CS). Infrared spectroscopy and chemical analysis results confirmed the non-stoichiometric profile of the synthesized HAp, with a 1.98 Ca/P ratio. X-ray diffraction (XRD) results showed that HAp and calcium oxide (CaO) crystalline phases were obtained and no residual starch was detected. Rietveld refinements confirmed that, for all three types of starch, the content of crystalline HAp was greater than 96.5% and the unit cell volume was not affected. Scanning electron microscopy (SEM) showed agglomeration of particles. Nanoparticle tracking analysis (NTA) results demonstrated that the use of SS produced the smallest particles (approximately 60nm).
Additive manufacture, also known as 3D printing, is a powerful and versatile tool to fabricate three-dimensional objects, and many research fields have been exploring 3D printing techniques for diverse applications. One of the main advantages of additive manufacturing is the possibility of fabricating tailored parts for specific applications, allowing fast prototyping and flexibility to the process. For energy conversion applications, additive manufacturing has been studied to produce versatile 3D printed electrodes and electrochemical cells, which can be applied to the production of green hydrogen through water splitting. In this chapter, the versatility of 3D printing towards the production of green hydrogen is explored, presenting the main filaments used to produce 3D printed electrodes and the strategies reported to functionalize these electrodes and improve their electrochemical activity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.