Electrochemical Bi/BiPO₄ Cells for a Sustainable Phosphate Cycle

Phosphorus is one of the main components of fertilizer and is also essential for various industrial manufacturing processes. While a continued increase in human population will require more fertilizer production, global phosphate rock reserves are limited. Furthermore, the collection of phosphate rock, its conversion to phosphoric acid, and disposal of phosphate create various environmental concerns. Here, we demonstrate intriguing electrochemical properties of Bi/BiPO4 electrodes which are used to construct phosphate removal and recovery cells. The Bi/BiPO4 cells selectively remove phosphate from a solution via a phosphate-specific electrode reaction and directly recover it as phosphoric acid without needing additional acid or generating any byproduct wastes. This discovery offers an unprecedented opportunity to produce phosphoric acid using phosphate wastes, which can lead to a sustainable phosphate cycle

A Comparative Study of Nickel, Cobalt, and Iron Oxyhydroxide Anodes for the Electrochemical Oxidation of 5‑Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

2,5-Furandicarboxylic acid (FDCA) has received increasing attention as a near-market platform chemical that can potentially replace terephthalic acid in the production of commercial and high-performance polymers, such as polyethylene terephthalate. FDCA can be obtained from the oxidation of 5-hydroxymethylfurfural (HMF), which is produced from the dehydration of C-6 monosaccharides obtained from cellulosic biomass. Recently, various heterogeneous Ni- and Co-based electrocatalysts were reported that can efficiently oxidize HMF to FDCA. The actual catalytically active species of these catalysts are most likely NiOOH and CoOOH or species related to NiOOH and CoOOH. However, the intrinsic catalytic properties of NiOOH and CoOOH for HMF oxidation have yet to be carefully and systematically investigated. In this study, we prepared thin and thick sets of NiOOH, CoOOH, and FeOOH films having comparable numbers of metal sites to systematically and methodically compare the intrinsic catalytic activity of these materials for HMF oxidation in a 0.1 M KOH (pH 13) solution. Our investigation revealed that they have distinctively different catalytic abilities for HMF oxidation. The use of extremely thin MOOH films containing limited numbers of catalytic sites allowed us to resolve anodic currents that were generated from HMF oxidation by different oxidation pathways. By comparing the voltammetric results of thin and thick films, the effect of the film thickness on the current generated by different oxidation pathways could be observed. The thick set of MOOH films was also used to compare the performances of these films for constant potential HMF oxidation and product analysis. The work herein contributes to a better understanding of the mechanisms of HMF oxidation on Ni-, Co-, and Fe-containing heterogeneous electrocatalysts whose surfaces are covered by their hydroxide and oxyhydroxide phases

A Desalination Battery Combining Cu₃[Fe(CN)₆]₂ as a Na-Storage Electrode and Bi as a Cl-Storage Electrode Enabling Membrane-Free Desalination

A desalination battery is an attractive route for seawater desalination because it couples ion removal with energy storage. In this work, we paired Cu3[Fe­(CN)6]2·nH2O as the Na-storage electrode with Bi as the Cl-storage electrode to construct a novel desalination battery that enables membrane-free desalination. Most current desalination technologies, with the exception of thermal distillation, rely on the use of membranes. Eliminating the need for a membrane can significantly simplify the construction and maintenance of desalination systems. After carefully examining the sodiation/desodiation reactions and cycle performance of Cu3[Fe­(CN)6]2·nH2O in both acidic and neutral saline solutions (0.6 M NaCl), we combined Cu3[Fe­(CN)6]2·nH2O with Bi, which was previously identified as a promising Cl-storage electrode, to construct a Cu3[Fe­(CN)6]2·nH2O/Bi desalination battery. The Cu3[Fe­(CN)6]2·nH2O/Bi desalination battery generates an electrical energy output during desalination, which is equivalent to discharging, and requires an electrical energy input during salination, which is equivalent to charging. We investigated optimum pH conditions to perform salination to minimize the energy necessary for charging so that the desalination/salination cycle could be achieved with a minimum overall energy input. The results obtained in this study suggest that with further optimization the Cu3[Fe­(CN)6]2·nH2O/Bi desalination battery will offer new possibilities for practical seawater desalination

Template-Free Electrochemical Synthesis of Sn Nanofibers as High-Performance Anode Materials for Na-Ion Batteries

Sn nanofibers with a high aspect ratio are successfully synthesized using a simple electrodeposition process from an aqueous solution without the use of templates. The synthetic approach involves the rapid electrochemical deposition of Sn accompanied by the strong adsorption of Triton X-100, which can function as a growth modifier for the Sn crystallites. Triton X-100 is adsorbed on the {200} crystallographic planes of Sn in an elongated configuration and suppressed the preferential growth of Sn along the [100] direction. Consequently, the Sn electrodeposits are forced to grow anisotropically in a direction normal to the (112) or (1̅12) plane, forming one-dimensional nanofibers. As electrode materials for the Na-ion batteries, the Sn nanofibers exhibit a high reversible capacity and an excellent cycle performance; the charge capacity is maintained at 776.26 mAh g^–1 after 100 cycles, which corresponds to a retention of 95.09% of the initial charge capacity. The superior electrochemical performance of the Sn nanofibers is mainly attributed to the high mechanical stability of the nanofibers, which originate from highly anisotropic expansion during sodiation and the pore volumes existing between the nanofibers

Electrochemically Synthesized Sb/Sb₂O₃ Composites as High-Capacity Anode Materials Utilizing a Reversible Conversion Reaction for Na-Ion Batteries

Sb/Sb₂O₃ composites are synthesized by a one-step electrodeposition process from an aqueous electrolytic bath containing a potassium antimony tartrate complex. The synthesis process involves the electrodeposition of Sb simultaneously with the chemical deposition of Sb₂O₃, which allows for the direct deposition of morula-like Sb/Sb₂O₃ particles on the current collector without using a binder. Structural characterization confirms that the Sb/Sb₂O₃ composites are composed of approximately 90 mol % metallic Sb and 10 mol % crystalline Sb₂O₃. The composite exhibits a high reversible capacity (670 mAh g^–1) that is higher than the theoretical capacity of Sb (660 mAh g^–1). The high reversible capacity results from the conversion reaction between Na₂O and Sb₂O₃ that occurs additionally to the alloying/dealloying reaction of Sb with Na. Moreover, the Sb/Sb₂O₃ composite shows excellent cycle performance with 91.8% capacity retention over 100 cycles, and a superior rate capability of 212 mAh g^–1 at a high current density of 3300 mA g^–1. The outstanding cycle performance is attributed to an amorphous Na₂O phase generated by the conversion reaction, which inhibits agglomeration of Sb particles and acts as an effective buffer against volume change of Sb during cycling