Cobalt Phosphates and Applications

*Riadh Marzouki, Mahmoud A. Sayed, Mohsen Graia and Mohamed Faouzi Zid*

### **Abstract**

Cobalt phosphates with open framework present various physical performances in relation to their structures. In fact, the development of new materials that could potentially be ionic conductors or ion exchangers led us to examine the Co-P-O and A-Co-P-O crystallographic systems (A: monovalent cation) and their different methods of synthesis. This work consists first of all in highlighting the crystalline phases of cobalt phosphates. Indeed, many works related to the discovery of some of these materials with interesting properties, in particular ionic conductivity, motivated our research and encouraged us to collect several cobalt phosphates and to correlate structure-physical properties in particular electrical properties.

**Keywords:** cobalt phosphate, structure, open framework, physical property, battery

#### **1. Introduction**

The search for new inorganic materials with open frameworks formed by tetrahedra and octahedra sharing corners or edges; delimiting cages (1D), interlayer spaces (2D), or tunnels (3D); or communicating by the intermediate of windows where cations are located is an interesting field with intense activity including several disciplines: solid-state chemistry, physics, mechanics, etc. Synthesis and physicochemical studies of metallophosphate compounds are the driving force behind the recent technological development, and studies are progressing through the exchange of points of view between specialists concerned.

Metallophosphates have a promising field for various applications: electrical, electrochemical, magnetic, and catalytic processes [1–7]. Nevertheless, the introduction of monovalent ions into metallophosphates can lead to materials with interesting properties. This orientation was initiated from the discovery of the ionic conduction properties of NASICON Na3Zr2Si2PO12 (σ300°C = 0.2 S cm<sup>−</sup><sup>1</sup> and Ea = 0.29 eV) in 1976 [5] followed by olivine series studies of general formula LiMPO4 (M = Co2+, Fe2+, Mn2+) usable in the manufacture of cathodes of rechargeable lithium-ion batteries [7]. These materials have a remarkable structural richness: olivine structure [7], zeolitic structure [8], alluaudite structure [9], melilite structure [10], etc. In relation to their structures, these materials have many physicochemical properties: ionic conduction [10], ion exchange [6, 7], etc. In this context, several researcher groups have tried to explore CoO-P2O5 and A2O-CoO-P2O5 systems (A: monovalent metals). This chapter is dedicated to treated physicochemical and structural studies of monovalent cation cobalt phosphates (Li, Na, K, and Ag).
