Fabrication of niobium-based oxides/oxynitrides/nitrides and their applications in dye-sensitized solar cells and anaerobic digestion

Abstract Transition metal compounds (TMCs), as a representative family of functional materials, have attracted great attention in the field of renewable energy. Herein, Nb 3.49 N 4.56 O 0.44 and NbN are prepared from the nitridation of NbO 2 in an NH 3 atmosphere. These dual-functional Nb-based compounds were applied to dye-sensitized solar cells (DSSCs) and anaerobic digestion (AD), and the efficiency and stability of these DSSCs and AD systems were systematically evaluated. The Nb 3.49 N 4.56 O 0.44 counter electrode (CE) exhibited considerable electrocatalytic activity and stability in I 3 − reduction in DSSCs, achieving photovoltaic performance comparable with Pt (6.36% vs. 7.19%). Furthermore, as accelerants, Nb-based compounds can greatly improve the AD environment, increasing substrate utilization and decreasing the hazards in the digestate. Compared with the control sample (409.2 mL/g·VS and 29.55%), substantially higher cumulative biogas production (437.1–522.7 mL/g·VS) and chemical oxygen demand removal rates (56.08%–65.19%) were achieved using Nb-based accelerants in the AD system. The nitridation technique is an effective and general means of converting Nb-based oxides into oxynitrides and nitrides. The Nb-based compounds with high electrocatalytic activities showed promise for DSSCs applications, while greatly enhancing the biodegradability of the AD system as accelerants. These findings could pave the way for multifunctional applications of TMCs in renewable energy fields.