Exclusive Hydrogen Generation by Electrocatalysts Coated with an Amorphous Chromium-Based Layer Achieving Efficient Overall Water Splitting

Abstract

Successful conversion of renewable energy to useful chemicals requires efficient devices that can electrocatalyze or photocatalyze redox reactions, e.g., overall water splitting. Excellent electrocatalysts for the hydrogen evolution reaction (HER), such as Pt, can also cause other sidereactions, including the water-forming back-reaction from H 2 and O 2 products. A Cr-based amorphous layer coated on catalysts can work as a successful surface modifier that avoids the back-reaction, but its capabilities and limitations toward other species have not been studied. Herein, we investigated the Cr-based layer on Pt from perspectives of both electrocatalysis and photocatalysis using redox-active molecules/ions (O 2 , ferricyanide, IO 3, H 2 O 2 , and CO gas). Our systematic study revealed that utilization of the Cr-based layer realized an exclusive cathodic reaction only to HER, even in the presence of the aforementioned reactive species, suggesting that Cr-based layers work as membranes, as well as corrosion and poison inhibition layers. However, the Crbased layer experienced self-oxidation and dissolved into the aqueous phase when a strong oxidizing agent or low pH was present. Presented herein are fundamental and critical aspects of the Cr-based modifier, which is essential for the successful and practical development of solar fuel production systems.

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

“…The diffusion‐limiting current density for the oxygen reduction reaction (ORR) was ≈−5 mA cm −2 on a bare Pt electrode (Figure d). The suppression of ORR by the CrO x layer is consistent with previous reports and is explained by the unique permselectivity through the layer . The CrO x layer prevents the diffusion of O 2 while allowing the mass‐transport of the protons and H 2 .…”

“…The suppression of ORR by the CrO x layer is consistent with previous reports and is explained by the unique permselectivity through the layer. [35][36][37] The CrO x layer prevents the diffusion of O 2 while allowing the mass-transport of the protons and H 2 . The cyclic voltammograms measured before and after the stability test remained unchanged (Figure 6d), which also indicate the excellent stability of CrO x during the HER in the presence of O 2 .…”

“…A crossover could take place on the cathode, where the oxidized Fe 3+ ‐HEDTA ion can be reduced instead of the HER. To avoid the crossover, a nano‐membrane coating was applied on the HER catalyst (bottom image in Figure ), which prevents the diffusion of large redox ions from reaching the electrocatalyst underneath while allowing protons and hydrogen to go through . In this study, CrO x was employed as a model nano‐membrane layer for the ion‐exchange‐membrane‐free device because of its well‐known functionality in corrosion protection, photocatalytic water splitting, and electrochemical chlorate production .…”

“…To avoid the crossover, a nano-membrane coating was applied on the HER catalyst (bottom image in Figure 1), which prevents the diffusion of large redox ions from reaching the electrocatalyst underneath while allowing protons and hydrogen to go through. [35][36][37][38][39][40][41][42] In this study, CrO x was employed as a model nano-membrane layer for the ion-exchange-membrane-free device because of its well-known functionality in corrosion protection, photocatalytic water splitting, and electrochemical chlorate production. [35][36][37]43,44] The applicability of CrO x to the present application is also discussed.…”

Photocatalytic overall water splitting using modified SrTiO3

“…In these cases the use of complex core-shell structured materials will be redundant. 69,[84][85][86] From PEC studies it is even known that catalysts such as Mo2C 87 , MoSx 87,88 and other transition metal oxides 89 are suitable to achieve stable PEC performances. Most of these non-noble materials possess semiconducting properties 90 which will change the description of the semiconductor/co-catalyst interface.…”