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Green hydrogen production through the electrocatalytic hydrogen evolution reaction (HER) is a promising solution for transition from fossil fuels to renewable energy. To enable the use of a variety of electrolytes with different pH values, HER catalysts with pH universality are highly desirable but their performance remains mediocre. Herein, a pH‐universal HER catalyst composed of ruthenium nanoparticles decorated on amorphous Ni‐doped MoO3 (a–Ni–MoO3) nanowire support is reported, that is, Ru/a–Ni–MoO3, which achieves enhanced performance as compared to the commercial Ru/C catalyst. Electron transfer from Ru to a–Ni–MoO3 is identified by spectroscopic techniques, which results in a modified electronic structure of the Ru active sites with a reduced electron density of 4d states near the Fermi level. Density functional theory calculations further reveal that the modulated electronic structure weakens the interactions between the Ru active sites and the reaction intermediates, which facilitates the HER reaction steps including H intermediate desorption and water dissociation. Experimental and theoretical findings provide insight into enhancing pH‐universal HER performance through modulation of electrocatalyst electronic structure. [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]

Graphene edges exhibit a highly localized density of states that result in increased reactivity compared to its basal plane. However, exploiting this increased reactivity to anchor and tune the electronic states of single atom catalysts (SACs) remains elusive. To investigate this, a method to anchor Pt SACs with ultra‐low mass loadings at the edges of edge‐rich vertically aligned graphene (as low as 0.71 µg Pt cm–2) is developed. Angle‐dependent X‐ray absorption spectroscopy and density‐functional theory calculations reveal that edge‐anchored Pt SACs has a robust coupling with the π‐electrons of graphene. This interaction results in a higher occupancy of the Pt 5d orbital, shifting the d‐band center toward the Fermi level, improving the adsorption of *H for the hydrogen evolution reaction (HER). Pt primarily coordinated to the graphene edge shows improved alkaline HER performance compared to Pt coordinated in mixed environments (turnover frequencies of 22.6 and 10.9 s–1 at an overpotential of 150 mV, respectively). This work demonstrates an effective route to engineering the coordination environment of Pt SACs by using the graphene edge for enhanced energy conversion reactions. [ABSTRACT FROM AUTHOR]

Environmentally friendly routes from "Power‐to‐X" (P2X) technologies to sustainably harvest and store renewable energy with net‐zero CO2 emission are imperative. The concept of P2X relies on (photo)electrolysis of earth‐abundant molecules into value‐added products. For practical utilization, engineering robust, active, albeit inexpensive (photo)electrocatalysts via industrially compatible technologies is indeed crucial. In this context, flame spray pyrolysis (FSP) stands as an emerging approach for one‐step synthesis of ready‐to‐use (photo)electrocatalysts with production rates of Kg h‐1 in lab‐scales. While features of FSP to engineer nanomaterials have been summarised, there is a need for more critical discussions on key factors, modulating properties of flame‐made catalysts. Therefore, this review article will first provide an overview about the concept of the P2X and catalyst development strategies. Unique characteristic of flame‐synthesized nano‐catalysts including compositions, fractal morphologies, defects, and active sites will be then critically discussed. Furthermore, a potential of FSP as an electrode‐assembly technique for one‐step preparation of catalysts on gas diffusion layers for industry‐relevant electrolyser testing will be presented. Finally, perspectives on challenges and opportunities of FSP for renewable energies will be raised. This will provide insights into the versatility and commercial viability of the FSP route for engineering novel nanostructured catalysts for renewable energy applications. [ABSTRACT FROM AUTHOR]

In this study, scalable, flame spray synthesis is utilized to develop defective ZnO nanomaterials for the concurrent generation of H2 and CO during electrochemical CO2 reduction reactions (CO2RR). The designed ZnO achieves an H2/CO ratio of ≈1 with a large current density (j) of 40 mA cm−2 during long‐term continuous reaction at a cell voltage of 2.6 V. Through in situ atomic pair distribution function analysis, the remarkable stability of these ZnO structures is explored, addressing the knowledge gap in understanding the dynamics of oxide catalysts during CO2RR. Through optimization of synthesis conditions, ZnO facets are modulated which are shown to affect reaction selectivity, in agreement with theoretical calculations. These findings and insights on synthetic manipulation of active sites in defective metal‐oxides can be used as guidelines to develop active catalysts for syngas production for renewable power‐to‐X to generate a range of fuels and chemicals. [ABSTRACT FROM AUTHOR]

Renewable‐electricity‐powered electrocatalytic CO2 reduction reactions (CO2RR) have been identified as an emerging technology to address the issue of rising CO2 emissions in the atmosphere. While the CO2RR has been demonstrated to be technically feasible, further improvements in catalyst performance through active sites engineering are a prerequisite to accelerate its commercial feasibility for utilization in large CO2‐emitting industrial sources. Over the years, the improved understanding of the interaction of CO2 with the active sites has allowed superior catalyst design and subsequent attainment of prominent CO2RR activity in literature. This review tracks the evolution of the understanding of CO2RR active sites on different electrocatalysts such as metals, metal‐oxides, single atoms, metal‐carbon, and subsequently metal‐free carbon‐based catalysts. Despite the tremendous research efforts in the field, many scientific questions on the role of various active sites in governing CO2RR activity, selectivity, stability, and pathways are still unanswered. These gaps in knowledge are highlighted and a discussion is set forth on the merits of utilizing advanced in‐situ and operando characterization techniques and machine learning (ML). Using this technique, the underlying mechanisms can be discerned, and as a result new strategies for designing active sites may be uncovered. Finally, this review advocates an interdisciplinary approach to discover and design CO2RR active sites (rather than focusing merely on catalyst activity) in a bid to stimulate practical research for industrial application. [ABSTRACT FROM AUTHOR]

Abstract: Developing highly efficient and earth‐abundant electrocatalysts for the oxygen evolution reaction (OER) is critical in overall water splitting technology. Among all transition‐metal‐based materials, NiFe‐based electrocatalysts have been regarded as the most promising substitute to commercial noble metals in alkaline conditions. To overcome their leaching problem and improve intrinsic stability without compromising activity, we report a NiFe alloy covered with a discrete N‐doped graphitic shell for the OER. The alloy core@discrete graphitic shell structure exhibits enhanced OER activity and stability with a low onset potential of 1.48 V, reduced overpotential of 320 mV@10 mA cm−1, and small Tafel slope value of 41 mV dec−1, which is superior to Ir/C. It is believed that the nitrogen doping, a discrete graphitic shell, and a mesoporous structure work in harmony to enhance the OER performance. [ABSTRACT FROM AUTHOR]

A stable and selective electrocatalyst for CO2 reduction was fabricated by covalently attaching graphitic carbon nitride onto multiwall carbon nanotubes (g-C3N4/MWCNTs). The as-prepared composite is able to reduce CO2 exclusively to CO with a maximum Faraday efficiency of 60 %, and no decay in the catalytic activity was observed even after 50 h of reaction. The enhanced catalytic activity towards CO2 reduction is attributed to the formation of active carbon-nitrogen bonds, high specific surface area, and improved material conductivity of the g-C3N4/MWCNT composite. [ABSTRACT FROM AUTHOR]

Efficient and low-cost electrocatalysts for water splitting are essential for solar fuel production. Herein, we report that nanoarrays of CoP supported on carbon cloth are an efficient bifunctional catalyst for overall water splitting. The catalyst exhibits remarkable activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media, delivering a current density of 10 mA cm−2 at an overpotential of 281 mV for OER and 95 mV for HER. During electrocatalysis, the surface of the CoP catalyst was covered with a layer of CoO x, which was the active species. However, the CoP core and the nanoarray morphology contributed significantly to the activity. [ABSTRACT FROM AUTHOR]

The large‐scale application of electrochemical reduction of CO2, as a viable strategy to mitigate the effects of anthropogenic climate change, is hindered by the lack of active and cost‐effective electrocatalysts that can be generated in bulk. To this end, SnO2 nanoparticles that are prepared using the industrially adopted flame spray pyrolysis (FSP) technique as active catalysts are reported for the conversion of CO2 to formate (HCOO−), exhibiting a FEHCOO− of 85% with a current density of −23.7 mA cm−2 at an applied potential of −1.1 V versus reversible hydrogen electrode. Through tuning of the flame synthesis conditions, the amount of oxygen hole center (OHC; SnO●) is synthetically manipulated, which plays a vital role in CO2 activation and thereby governing the high activity displayed by the FSP‐SnO2 catalysts for formate production. The controlled generation of defects through a simple, scalable fabrication technique presents an ideal approach for rationally designing active CO2 reduction reactions catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spinel Co 3 O 4 with tailored fractal, chemical and electronic properties. • A structure–activity-stability relationship is systematically studied. • Catalytic activity is bound to active species and sites, and a local electric field. • Evidence for the in-situ transformation to amorphous oxyhydroxide species. • Co 3 O 4 fractal performed high mass-normalized j of 1947 A g−1 @1.63 V vs RHE at 80 °C. Carbon-free production of hydrogen from renewable energy sources is readily attainable via electrochemical water splitting. Increasing the fraction of H 2 generated by such environmentally friendly routes requires, however, further progress in electrode design to overcome the limited stability and activity of earth-abundant electrocatalysts. Herein, we report the multiscale engineering of the properties of Co 3 O 4 electrocatalysts for oxygen evolution reaction (OER), revealing insights into the close interplay between activity and stability. The surface chemistry and physical properties of Co 3 O 4 electrodes such as Co2+/Co3+ ratio, fractal features, and electron conductivity are modulated by a highly scalable one-step hot-aerosol synthesis. Optimized Co 3 O 4 electrodes are obtained with a high mass-specific current density for OER of 642 A g−1 at 400 mV overpotential, which can be boosted to 1947 A g−1 at industrially-relevant elevated electrolyte temperature of 80 °C. Through operando Raman measurements, we reveal the in-situ transformation of the as-synthesized cobalt oxide moieties to oxyhydroxide species, identifying their role as catalytic active sites for OER. The potential of these earth-abundant electrocatalysts and their scalable preparation approach are demonstrated with a custom-designed electrolyzer, achieving a very high mass-specific current density of 800 A g−1 at 400 mV overpotential and more than 12 h stable operation. [ABSTRACT FROM AUTHOR]