A Stand‐Alone Module for Solar‐Driven H₂ Production Coupled with Redox‐Mediated Sulfide Remediation

Abstract

Efficient electrochemical devices are required to convert electric power by intermittent renewable energy sources into a chemical form. The choice of combination in reduction–oxidation reactions can vary depending on the target, which provides different thermodynamics and kinetics. A promising approach for H2 production coupled with sulfide remediation is demonstrated to utilize the intermediate redox media. H2 is produced on the cathode, and soluble redox ions in a reduced form are oxidized on the anode. The ions are then transferred to a separate reactor to oxidize the sulfide ions via a homogeneous reaction, and the reduced redox ions are recirculated. A solar‐driven redox photovoltaic‐electrochemical (PV‐EC) system is operated as a stand‐alone module and is composed of Cu(In,Ga)(S,Se)2 (CIGS) PVs and EC cells in series and operated under natural solar irradiation. A unique EC cell is established in an aqueous‐phase membraneless configuration at ambient temperature, and a cathode is decorated with a semipermeable CrOx‐based nanomembrane. This allows for selective H2 evolution without causing Fe redox reduction. Remaining issues associated with the stability of the CrOx permselective layer on the cathode are also discussed, which are associated with the formation constant of a soluble metal complex in the presence of ligand counterions.

Low-temperature direct electrochemical splitting of H2S

“…The potential difference between the H 2 evolution reaction (HER) and sulfur oxidation reaction (SOR) is only 0.14 V (Kelsall and Thompson, 1993), substantially lower than the theoretical 1.23 V necessary to drive water splitting (Kay et al, 2006). However, the overall energy required to drive H 2 S splitting depends not only on its thermodynamics but also on the electrochemical setup, given that it is largely affected by the ohmic and mass transport losses as well as kinetic overpotentials on the electrocatalysts (Obata et al, 2019). Proper selection of the electrochemical conditions is a crucial step for optimizing the energy expenditure of the process.…”

Prediction of Limits of Solar‐to‐Hydrogen Efficiency from Polarization Curves of the Electrochemical Cells

“…Equation (4) describes the voltage efficiency of an EC cell with a Faradaic efficiency of 100%, which is realistic for optimized experimental EC cells. [8,47,48] Although details of the hydrogen and oxygen evolution reactions during water splitting are still under debate, [2,49] we have assumed ΔE ¼ 1.23 V, which is widely used in the literature, [1,[6][7][8][9][10][11][19][20][21][22][23][31][32][33][34][35][43][44][45][46][47][48][50][51][52][53][54][55] to calculate the EC voltage efficiency. In this section, we address the coupling and STH limit problems using the absolute currents of both PV and EC devices as well as the absolute total irradiance P in , which is practical if both devices have predefined areas.…”

Catalytic effects of molybdate and chromate–molybdate films deposited on platinum for efficient hydrogen evolution

“…The selective permeability has been exploited to drive the photocatalytic degradation of harmful wastes (e.g. sulfide) 29 . Addition of Pt to chromium‐formed films is beneficial as an effective cocatalyst for photocatalytic water splitting 30 .…”

“…sulfide). 29 Addition of Pt to chromium-formed films is beneficial as an effective cocatalyst for photocatalytic water splitting. 30 Therefore, understanding the role of MoO x H y films and of their synergy with CrO x H y on catalytic reactions has a wide range of implications for sustainable fuel generation and the remediation of wastewater.…”