Considering the attractive optoelectronic properties of metal halide perovskites (MHPs), their introduction to the field of photocatalysis was only a matter of time. Thus far, MHPs have been explored for the photocatalytic generation of hydrogen, carbon dioxide reduction, organic synthesis, and pollutant degradation applications. Of growing research interest and possible applied significance are the currently emerging developments of MHP-based Zscheme heterostructures, which can potentially enable efficient photocatalysis of highly energy-demanding redox processes. In this Perspective, we discuss the advantages and limitations of MHPs compared to traditional semiconductor materials for applications as photocatalysts and describe emerging examples in the construction of MHP-based Z-scheme systems. We discuss the principles and material properties that are required for the development of such Z-scheme heterostructure photocatalysts and consider the ongoing challenges and opportunities in this emerging field.

The instability and expense of anodes for water electrolyzers with acidic electrolytes can be overcome through the implementation of a cobalt‐iron‐lead oxide electrocatalyst, [Co–Fe–Pb]Ox, that is self‐healing in the presence of dissolved metal precursors. However, the latter requirement is pernicious for the membrane and especially the cathode half‐reaction since Pb2+ and Fe3+ precursors poison the state‐of‐the‐art platinum H2 evolving catalyst. To address this, we demonstrate the invariably stable operation of [Co–Fe–Pb]Ox in acidic solutions through a cobalt‐selective self‐healing mechanism without the addition of Pb2+ and Fe3+ and investigate the kinetics of the process. Soft X‐ray absorption spectroscopy reveals that low concentrations of Co2+ in the solution stabilize the catalytically active Co(Fe) sites. The highly promising performance of this system is showcased by steady water electrooxidation at 80±1 °C and 10 mA cm−2, using a flat electrode, at an overpotential of 0.56±0.01 V on a one‐week timescale.

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Dye-sensitized photocathodes have been observed on several occasions to sustain light-driven H 2 generation without intentionally introduced catalysts. Herein, plausible mechanisms addressing this phenomenon are probed by a combination of long-term photoelectrochemical measurements with concurrent gas chromatography, transient absorption spectroscopy, and inductively coupled mass spectrometry using a perylenemonoimide-sexithiophene-triphenylamine (PMI-6T-TPA) sensitized NiO electrode. The experimental evidence obtained discounts the possibility for direct reduction of hydrogen by the dye and demonstrates that the availability of interfaces between dye molecules and any electrically disconnected NiO particles exposed to the electrolyte solution is critical for photoelectrocatalytic H 2 generation. These interfaces are postulated to serve as photoactive sites for the formation of a hydrogen evolution catalyst, e.g., metallic nickel, which can accept photogenerated electrons from the excited dye molecules. The Ni 0 catalyst can form via photoelectroreduction of Ni 2+ , which has been found to slowly dissolve from the NiO support into the solutions during the photoelectrochemical measurements. Additionally, dependence of the H 2 generation rate on the anion within the electrolyte has been identified, with the highest rates of 35-40 nmol h -1 cm -2 achieved with acetate. The origin of this dependence remains unsolved at this stage but is clearly demonstrated to be not associated with the different rates of dissolution of NiO, the presence of other transition metal contaminants, nor electronic impacts of the anion on the NiO valence band. Overall, the results herein demonstrate that the effects of the chemical nature of the electrolyte, metallic nickel deposited from dissolved Ni 2+ , and availability of the interfaces between disconnected NiO and adsorbed dye should be considered when interpreting the photoelectrocatalytic performance of dye-sensitized photocathodes for dihydrogen evolution. × Our colleague, mentor and friend Prof. Leone Spiccia has passed away before this work could be published. Leone was an outstanding researcher and personality, and is sadly missed. ABSTRACTDye-sensitized photocathodes have been observed on several occasions to sustain light-driven H2 generation without intentionally-introduced catalysts. Herein, plausible mechanisms addressing this phenomenon are probed by a combination of long-term photo-electrochemical measurements with concurrent gas chromatography, transient absorption spectroscopy and inductively coupled mass spectrometry using a perelenmonoimid-sexithiophene-triphenylamine (PMI-6T-TPA) sensitized NiO electrode. The experimental evidence obtained discounts the possibility for direct reduction of hydrogen by the dye and demonstrates that the availability of interfaces between dye molecules and any electrically-disconnected NiO particles exposed to the electrolyte solution is critical for photo-electrocatalytic H2 generation. These interfaces are postulated to serve as photo-a...

Development of catalysts for the oxygen evolution reaction (OER) that are capable of robust operation at low pH and elevated temperatures, but do not contain scarce ruthenium and iridium, presents a challenging yet very attractive strategy in decreasing the high cost of efficient water electrolyzers paired with proton-exchange electrolytes. Toward this aim, combinations of both catalytically active and acid-stable components offer an appealing approach to cost-effective anode catalysis for low-pH water electrolysis. The current work presents an oxygen-evolving [Ag + Bi]­O x catalyst based on intermixed silver and bismuth oxides, prepared by a simple anodic electrodeposition. We demonstrate that numerous electrode substrates can be functionalized and operate stably with the [Ag + Bi]­O x catalyst in nominally pure aqueous H2SO4 solutions. Moreover, this catalyst maintains robust operation at pH 0.3 and temperatures as high as 80 °C. Under these conditions, the [Ag + Bi]­O x catalyst can deliver an OER rate of 100 mA cm–2 at an overpotential of 0.70 ± 0.02 V vs reversible hydrogen electrode (RHE). In situ X-ray absorption spectroscopic and Fourier transformed alternating current cyclic voltammetric studies of the [Ag + Bi]­O x system demonstrate the stabilizing role of the bismuth oxide matrix that facilitates the transformation of silver into a highly oxidized state catalyzing the acidic water electrooxidation.

Aiming to design a catalyst for stable electrooxidation of water at low pH, the present work explores the properties and structural features of electrodeposited composite oxides based on Bi and Co, which were anticipated to provide stability and catalytical activity, respectively. Materials deposited as very thin (ca 50 nm) films on F-doped SnO 2 (FTO) substrate do not initially exhibit high activity in 0.1 M H 2 SO 4 , but are activated during operation through the electrooxidatively-induced enrichment of the catalytic surface with Co and Sn oxides. The latter originate from the FTO support and are identified as an important component of the catalyst through control experiments with a Sn-free substrate and with Sn 2 + intentionally added at the electrodeposition stage. A distinctive feature of the CoÀ BiÀ Sn-based electrocatalyst is the slow but persistent improvement in the activity during operation in 0.1 M H 2 SO 4 at both ambient and elevated (60 °C) temperatures, which contrasts with the continuously degrading behaviour of state-ofthe-art oxygen evolution catalysts at low pH. This is demonstrated by 9-day-long galvanostatic tests at 10 mA cm À 2 , during which the CoÀ BiÀ Sn-based thin film catalyst shows no degradation and sustains stable water oxidation at ca 1.9 V vs. reversible hydrogen electrode. The effects of tin leaching from the support detected herein might have implications to other acidic water oxidation catalysts supported on high-surface area doped SnO 2 materials.

Influence of the conditions for aerobic oxidation of Mn2+(aq) catalysed by the MnxEFG protein complex on the morphology, structure and reactivity of the resulting biogenic manganese oxides (MnO ) is explored. Physical characterisation of MnO includes scanning and transmission electron microscopy, and X-ray photoelectron and K-edge Mn, Fe X-ray absorption spectroscopy. This characterisation reveals that the MnO materials share the structural features of birnessite, yet differ in the degree of structural disorder. Importantly, these biogenic products exhibit strikingly different morphologies that can be easily controlled. Changing the substrate-to-protein ratio produces MnO either as nm-thin sheets, or rods with diameters below 20 nm, or a combination of the two. Mineralisation in solutions that contain Fe2+(aq) makes solids with significant disorder in the structure, while the presence of Ca2+(aq) facilitates formation of more ordered materials. The (photo)oxidation and (photo)electrocatalytic capacity of the MnO minerals is examined and correlated with their structural properties.

The possibility of efficient water electrooxidation sustained by continuous (re)generation of catalysts derived from the oxidative electrodeposition of transition‐metal contaminants is examined herein for three natural water samples from Australia and China. The metal composition of the solutions has been determined by inductively coupled plasma optical emission spectrometry, and a range of strategies to produce water‐splitting catalysts by means of in situ electrodeposition have been applied. The performance of the resulting electrocatalysts is below the state‐of‐the‐art level owing to large amounts of impurities in the solutions and non‐optimal concentrations of naturally available catalyst precursors. Nevertheless, these studies have identified the FePb‐based system as a rare example of an electrocatalyst for water oxidation that forms in situ and maintains reasonable activity (≥4.5 mA cm−2 at an overpotential of 0.8 V) in weakly acidic solutions (pH 2.9).