Search

Proton-exchange-membrane water electrolyzers (PEMWEs) produce high-purity H2, withstand load fluctuations, and operate with a pure-water feed but require platinum-group-metal catalysts for durability, such as IrO2 and Pt, due to the acidic environment. At the anode, the slow oxygen evolution reaction (OER) requires a high overpotential to achieve relevant current densities (>2 A·cm-2) even with a high loading of IrO2. Using a simple commercial 1,5-cyclooctadiene iridium chloride dimer precursor, we synthesized submonolayer-thick IrOx on the surfaces of conductive metal oxides to make every Ir atom available for catalysis and reach the ultimate lower limit for Ir loading. We show that the reaction on Sb/SnO2 and F/SnO2 conductive oxides is surface-limited and that a continuous Ir-O-Ir network provides improved stability and activity. We cover IrOx with a thin layer of acid-stable TiOx by atomic-layer deposition. The effects of TiOx on the catalyst’s performance were assessed by inductively coupled plasma mass spectrometry (ICP-MS) coupled in situ with an electrochemical flow cell and ex situ by X-ray photoelectron spectroscopy. Tuning the binding environment of IrOx by TiOx addition enhances the intrinsic activity of the active sites, simultaneously accelerating the dissolution of the catalyst and the metal-oxide support. We illustrate the interplay between the support, catalyst, and protection-layer dissolution with OER activity, and highlight the effects of annealing to densify the TiOx protection layer on stability/activity. These ultrathin supported Ir-based catalysts do not eliminate the long-standing issue of the catalyst and support instability during OER in acids, but do provide new insight into the catalyst-support interactions and may also be of utility for advanced spectroscopic investigations of the OER mechanism.

The electrochemical applications of gold span the entire pH spectrum. Recently, gold dissolution in acidic and alkaline media has been studied, but less attention has been given to electrolytes at intermediate pH values. To address this gap, this work uses on‐line electrochemical dissolution inductively coupled plasma mass spectrometry (ICP‐MS) to examine gold dissolution across a pH range of 1 to 12.7 using phosphate buffer solutions. All experimental parameters, except pH, are kept constant, enabling a clear investigation of pH effects on anodic (gold oxidation) and cathodic (gold oxide reduction) dissolution processes. Results show that dissolution amounts are lowest at neutral pH values between 3 and 7, varying with the applied potential and exposure time. Anodic and cathodic dissolution dominate in acidic and alkaline electrolytes, respectively. Depending on the highest applied potentials and time exposure, the main dissolution mechanism shifts at pH=5, 7, and 9. The pH dependence of Au dissolution is proposed to be linked to the nature of gold oxides formed, the kinetics of oxide formation/reduction, gold ion redeposition, and the influence of the oxygen evolution reaction (OER) on dissolution. These results provide fundamental insights into gold dissolution under neutral pH conditions. [ABSTRACT FROM AUTHOR]

Automated platforms assessing the stability of electrocatalysts are key to accelerate the deployment of clean energy technologies. Here, we present a robust system that allows the study of corrosion behavior in conjunction with the electrochemical protocol and electrolyte composition over many individual electrodes. Oxygen reduction reaction on Pt is used as a proof-of-concept platform, where the influence of the potential window and phosphoric acid (PA) addition on Pt dissolution is probed. A total of 72 hours of automated operation was realized with actions including liquid management, cell cleaning, aliquoting, PA injection, and bubble detection and removal, demonstrating further advancements in automated stability testing for electrocatalysts. [ABSTRACT FROM AUTHOR]

The widespread application of green hydrogen production technologies requires cost reduction of crucial elements. To achieve this, a viable pathway to reduce the iridium loading in proton exchange membrane water electrolysis (PEMWE) is explored. Herein, a scalable synthesis method based on a photodeposition process for a TiO2@IrOx core–shell catalyst with a reduced iridium content as low as 40 wt.% is presented. Using this synthesis method, titania support particles homogeneously coated with a thin iridium oxide shell of only 2.1 ± 0.4 nm are obtained. The catalyst exhibits not only high ex situ activity, but also decent stability compared to commercially available catalysts. Furthermore, the unique core–shell structure provides a threefold increased electrical powder conductivity compared to structures without the shell. In addition, the low iridium content facilitates the fabrication of sufficiently thick catalyst layers at decreased iridium loadings mitigating the impact of crack formation in the catalyst layer during PEMWE operation. It is demonstrated that the novel TiO2@IrOx core–shell catalyst clearly outperforms the commercial reference in single‐cell tests with an iridium loading below 0.3 mgIr cm−2 exhibiting a superior iridium‐specific power density of 17.9 kW gIr−1 compared to 10.4 kW gIr−1 for the commercial reference. [ABSTRACT FROM AUTHOR]

Global demand for more effective methods to reclaim gold from electronic waste (E‐waste) has never been greater. Alternatives to hydrometallurgical methods, such as cyanide, are still limited. This work examines utilizing ozone and chlorides to recycle Au from E‐waste. It is started with a fundamental investigation of Au dissolution processes on the extended surface of Au polycrystalline and Au nanoparticulated electrodes. An online electrochemical scanning flow cell coupled with inductively coupled plasma mass spectrometry quantifies the rates and amounts of Au leaching. Identical‐location scanning electron microscopy (IL‐SEM) further correlates dissolution events with electrode morphological changes. It is demonstrated that ozone in the electrolyte imposes an anodic potential on the electrode, leading to anodic Au dissolution. Passivation disappears when small amounts of chlorides are added to the electrolyte, significantly enhancing the leaching yield. IL‐SEM images of gold nanoparticles (NPs) before and after exposure to ozone reveal heterogeneity in NP size‐dependent dissolution, showing higher dissolution for smaller particles. An effective Au leaching procedure is further demonstrated in a lab‐scale reactor using real E‐waste where almost complete recovery of Au is achieved. This research suggests that with engineering optimization in reactor applications based on ozone‐stimulated gold, dissolution can pave the way for environmentally friendly gold recycling. [ABSTRACT FROM AUTHOR]