Electrochemical, Spectroscopic, and Computational Investigations on Redox Reactions of Selenium Species on Galena Surfaces

Materials interacting with inorganic selenium from the perspective of electrochemical sensing

Inorganic selenium, the most common form of harmful selenium in the environment, can be determined using electrochemical sensors, which are compact, fast, reliable and easy-to-operate devices. Despite progress in this area, there is still significant room for developing high-performance selenium electrochemical sensors. To achieve this, one should take into account (i) the electrochemical process that selenium undergoes on the electrode; (ii) the valence state of selenium species in the sample and (iii) modification of the sensor surface by a material with high affinity to selenium. The goal of this review is to provide a knowledge base for these issues. After the Introduction section, mechanisms and principles of the electrochemical reduction of selenium are introduced, followed by a section introducing the modification of electrodes with materials interacting with selenium and a section dedicated to speciation methods, including the reduction of non-detectable Se(VI) to detectable Se(IV). In the following sections, the main types of materials (metallic, polymers, hybrid (nano)materials…) interacting with inorganic selenium (mostly absorbents) are reviewed to show the diversity of properties that may be endowed to sensors if the materials were to be used for the modification of electrodes. These features for the main material categories are outlined in the conclusion section, where it is stated that the engineered polymers may be the most promising modifiers.

FeCoSe2 Nanoparticles Embedded in g-C3N4: A Highly Active and Stable bifunctional electrocatalyst for overall water splitting

To investigate cost affordable and robust HER and OER catalysts with significant low overpotentials, we have successfully embedded FeCoSe2 spheres on smooth surfaces of graphitic carbon nitride that demonstrated high stability and electrocatalytic activity for H2 production. We systematically analyzed the composition and morphology of FexCo1-xSe2/g-C3N4 and attributed the remarkable electrochemical performance of the catalyst to its unique structure. Fe0.2Co0.8Se2/g-C3N4 showed a superior HER activity, with quite low overpotential value (83 mV at -20 mA cm-2 in 0.5 M H2SO4) and a current density of -3.24, -7.84, -14.80, -30.12 mA cm-2 at 0 V (vs RHE) in Dulbecco's Phosphate-Buffered Saline (DPBS), artificial sea water (ASW), 0.5 M H2SO4 and 1 M KOH, respectively. To the best of our knowledge, these are the highest reported current densities at this low potential value, showing intrinsic catalytic activity of the synthesized material. Also, the catalyst was found to deliver a high and stable current density of -1000 mA cm-2 at an overpotential of just 317 mV. Moreover, the synthesized catalyst delivered a constant current density of -30 mA cm-2 for 24 h without any noticeable change in potential at -0.2 V. These attributes confer our synthesized catalyst to be used for renewable fuel production and applications.