**Paweł P. Włodarczyk \* and Barbara Włodarczyk \***

Institute of Environmental Engineering and Biotechnology, Faculty of Natural Sciences and Technology, University of Opole, Kominka Str. 6, 45-032 Opole, Poland

**\*** Correspondence: pawel.wlodarczyk@uni.opole.pl (P.P.W.); barbara.wlodarczyk@uni.opole.pl (B.W.); Tel.: +48-077-401-6717 (P.P.W.)

Received: 31 October 2019; Accepted: 5 December 2019; Published: 8 December 2019

**Abstract:** Microbial fuel cells (MFCs) are devices than can contribute to the development of new technologies using renewable energy sources or waste products for energy production. Moreover, MFCs can realize wastewater pre-treatment, e.g., reduction of the chemical oxygen demand (COD). This research covered preparation and analysis of a catalyst and measurements of changes in the concentration of COD in the MFC with a Ni–Co cathode. Analysis of the catalyst included measurements of the electroless potential of Ni–Co electrodes oxidized for 1–10 h, and the influence of anodic charge on the catalytic activity of the Ni–Co alloy (for four alloys: 15, 25, 50, and 75% concentration of Co). For the Ni–Co alloy containing 15% of Co oxidized for 8 h, after the third anodic charge the best catalytic parameters was obtained. During the MFC operation, it was noted that the COD reduction time (to 90% efficiency) was similar to the reduction time during wastewater aeration. However, the characteristic of the aeration curve was preferred to the curve obtained during the MFC operation. The electricity measurements during the MFC operation showed that power equal to 7.19 mW was obtained (at a current density of 0.47 mA·cm<sup>−</sup>2).

**Keywords:** Ni–Co catalyst; oxygen electrode; microbial fuel cell; environmental engineering; electricity production
