Molecular hydrogen production from wastewater electrolysis cell with multi-junction BiOx/TiO2 anode and stainless steel cathode: Current and energy efficiency

Abstract

Electrochemical hydrogen evolution reaction (HER) has been recognized as a viable approach to generate a clean energy fuel. However, substantial technical breakthroughs are needed to reduce the costs for electricity and chemical reagents. In this study, we explore a specific wastewater electrolysis cell (WEC) as an alternative of decentralized H 2 production coupled with onsite water treatment. A prototypical WEC consists of a multi-junction semiconductor anode and a stainless steel cathode paired in single compartment cell. A distinct layer of BiO x /TiO 2 on anode surface had relatively low crystallinity that was shown to be beneficial for higher oxide formation and O 2 evolution. The over-potential and Tafel slope of the BiO x /TiO 2 anode were determined to be 0.32 V and 120 mV decade-1. In a single compartment WEC with a NaCl electrolyte ([Cl-] ≤ 50 mM), the current density (j) ranged up to 500 A m-2 at cell voltages less than 6 V, while the current efficiency (CE) for free chlorine (FC) evolution showed maximum value near 0.3. The CE and energy efficiency (EE) for the HER were assessed using NaCl solutions (50 mM with or without 2.5 g L-1 urea) and real wastewater with variable compositions ([Cl-]: 6 ~ 33 mM, [chemical oxygen demand]: 60 ~ 790 mg L-1). The ohmic resistance of wastewater electrolyte rules out the usage of membrane separation, resulting in side reactions such as reduction of O 2 whose CE values monotonically decreased with an increasing j under the diffusion controlled regime. Chloride ions reduce the electron consumption during O 2 reduction, while elevated levels of FC significantly lower the CE for the HER. The combined presence of oxidizable organic compounds and Clenhance the CE for the HER as long as the concentration of organics is enough to quench FC to maintain a pseudo steady-state concentration. The highest CE (0.8) and EE (0.23) for HER were observed during electrolysis of real wastewater at j values exceeding 200 A m-2. However, a dependency of value of EE on the applied cell voltage needs to be addressed further.

Bio‐reduced GO /Pd nanocomposite as an efficient and green synthesized catalyst for hydrogen evolution reaction

“…Although water electrolysis constitutes a small part of the world hydrogen production, its tendency is increasing day by day because of zero carbon emissions 1‐3 . The purity of hydrogen produced by the water electrolysis is very high, the method is simple and it ensures the development of the fuel cell technology 4‐9 . Beside these remarkable properties, the main disadvantage of the hydrogen production by the water electrolysis is the high energy consumption and consequently the low catalytic activity.…”

Hydrogen Environmental Benefits Depend on the Way of Production: An Overview of the Main Processes Production and Challenges by 2050

“…Then, the electrons migrate to the cathode where hydrogen is produced by the reduction of protons. [124] In this system, usually powered by PV cells, the organic pollutants can be eliminated through a direct or indirect process. [125] During the H 2 O oxidation to O 2 , some intermediates are formed (reactive oxygen species [ROS]).…”

Urea - Hydrogen Compost Soil Microbial Fuel Cell for Multifunctional Applications

“…The catalytic activities were found to be at ± 0.1 to 0.6 V range for urea and ± 0.5 V for the ammonium ions [5]. Both urea and ammonium ions are related to each other as sources of nitrogen and as fuel for accelerating the process of power generation used this time [3,4,[9][10][11][12].…”

“…The focus is to get power from the UH-CSMFC in coming future by using waste like urea rich wastewater, urine, industrial wastewater, which contains much amount of urea and a huge source of hydrogen storage. [1][2][3][4][5][6][7][8][9][10][11][12][13][44][45][46][47][48][49][50][51][52][53][54][55].…”

“…Therefore, compost soil is preferred for minimizing the risks, and less fuel and get more work and more power as compared to the liquid state. Furthermore, the reliable sources are usually cheaper and pose no issues with volatilization; moreover, it is easy to maintain the pH levels in the soil as solid-state [7][8][9][10][11]. Among all the available resources of sustainable energy, urea is a suitable fuel for MFCs.…”