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Highlights: A rational design of metal halide perovskites for achieving efficient CO2 reduction reaction was demonstrated. The stability of CsPbI3 perovskite nanocrystal (NCs) in aqueous electrolyte was improved by compositing with reduced graphene oxide (rGO). The CsPbI3/rGO catalyst exhibited > 92% Faradaic efficiency toward formate production with high current density which was associated with the synergistic effects between the CsPbI3 NCs and rGO. Transformation of greenhouse gas (CO2) into valuable chemicals and fuels is a promising route to address the global issues of climate change and the energy crisis. Metal halide perovskite catalysts have shown their potential in promoting CO2 reduction reaction (CO2RR), however, their low phase stability has limited their application perspective. Herein, we present a reduced graphene oxide (rGO) wrapped CsPbI3 perovskite nanocrystal (NC) CO2RR catalyst (CsPbI3/rGO), demonstrating enhanced stability in the aqueous electrolyte. The CsPbI3/rGO catalyst exhibited > 92% Faradaic efficiency toward formate production at a CO2RR current density of ~ 12.7 mA cm−2. Comprehensive characterizations revealed the superior performance of the CsPbI3/rGO catalyst originated from the synergistic effects between the CsPbI3 NCs and rGO, i.e., rGO stabilized the α-CsPbI3 phase and tuned the charge distribution, thus lowered the energy barrier for the protonation process and the formation of *HCOO intermediate, which resulted in high CO2RR selectivity toward formate. This work shows a promising strategy to rationally design robust metal halide perovskites for achieving efficient CO2RR toward valuable fuels. [ABSTRACT FROM AUTHOR]

Photoelectrochemical water splitting is a promising approach to produce green hydrogen using solar energy. A primary bottleneck remains the lack of efficient photoanodes to catalyze the sluggish water photooxidation reaction. Engineering photoabsorbers with a narrow bandgap and suitable band edge can boost the photoelectrochemical performance. Herein, nanostructured iron tungstate (FeWO4) photoanodes are engineered directly on a fluorine doped tin oxide glass substrate via a scalable and ultra-fast flame synthesis route in 13 seconds. Physiochemical, optoelectronic, and electrochemical properties of these photoanodes are systematically investigated. The key roles of charge transport, transfer, and dissolution of W and Fe ions from the FeWO4 matrix within long-term performance are revealed. Optimal FeWO4 photoanode with a bandgap of 1.82 eV and a FeOOH/NiOOH co-catalyst coating shows an improved water photooxidation performance, reaching a photocurrent density of 0.23 mA cm-2 at 1.4 V versus reversible hydrogen electrode in 1 m potassium hydroxide. It further demonstrates relatively good photostability, maintaining ≈96% of photocurrent density after 1-hour continuous photooxidation, albeit some trace of Fe, W and Ni elements dissolution. Insights on the photooxidation performance of nanostructured FeWO4 provide promising directions for the engineering of small band-gap catalysts for a variety of photoelectrochemical applications. [ABSTRACT FROM AUTHOR]

The electrochemical conversion of NOx (including NO3– and NO2–) to ammonium using renewable energy is emerging as a green alternative pathway for decarbonization of high emission industry to meet net zero emission targets. The key to efficient NOx electrolysis relies on the understanding of surface chemistry to establish the structure–activity relationships that will govern future scaleup of this process. In this work, we have undertaken a mechanistic investigation, wherein by tuning the surface oxidation state of CuOx nanoparticles on Cu foam (referred as CuOx/CuF), we are able to investigate its impact on conversion of NOx to ammonium (NH4+) under acidic reaction conditions. Supported by in situ Raman measurements, we reveal the importance of tuning the Cu oxidation state to maximize Cu2O formation, which forms beneficial Cu2O/Cu interfaces during reaction, allowing an enhanced NH4+ yield with a production rate of 45 nmol s–1 cm–2 and Faradaic efficiency (FENH4+) of 83% at −0.5 V vs RHE. Further, we reveal the promising stability of such interfaces under acidic conditions during long-term electrolysis for usage of up to 20 h. [ABSTRACT FROM AUTHOR]

Oxide-derived Cu catalysts from Cu2O microcrystals are capable of electro-chemically converting CO2 into various value-added chemicals. However, their structural transformation and associated preferred products remain unclear, requiring further investigation. Herein, Cu2O microcrystals with controllable low- and high-index facets exposure are fabricated to differentiate the effects of initial exposed facets on their structural reconstruction and product selectivity in electrochemical CO2 reduction reaction. Combined in situ characterizations and theoretical investigation reveal the direct correlations of Cu2O reconstruction and product selectivity to its initial facet exposure. The Cu2O low-index facet, being more stable with a high energy barrier on material reduction, tends to partially maintain its original crystalline structure and larger Cu2O particle size throughout the transformation. The derived flatter surface and limited Cu2O/ Cu interfaces result in a favorable selectivity toward 2-electron transfer products. The chemically active Cu2O high-index facet (311) is energetically favorable to be reduced owing to the feasible protonation process, thus experiencing a drastic reconstruction with rich newly formed Cu nanoparticles and evolved fine Cu2O grains; Such a reconstruction creates uncoordinated Cu species and abundant boundaries, benefiting charge transfer and increasing the local pH by confining OH-, thus leading to a high selectivity toward C2+ products. [ABSTRACT FROM AUTHOR]

MXenes, due to their tailorable chemistry and favourable physical properties, have great promise in electrocatalytic energy conversion reactions. To exploit fully their enormous potential, further advances specific to electrocatalysis revolving around their performance, stability, compositional discovery and synthesis are required. The most recent advances in these aspects are discussed in detail: surface functional and stoichiometric modifications which can improve performance, Pourbaix stability related to their electrocatalytic operating conditions, density functional theory and advances in machine learning for their discovery, and prospects in large scale synthesis and solution processing techniques to produce membrane electrode assemblies and integrated electrodes. This Review provides a perspective that is complemented by new density functional theory calculations which show how these recent advances in MXene material design are paving the way for effective electrocatalysts required for the transition to integrated renewable energy systems. [ABSTRACT FROM AUTHOR]