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HighlightsThe crystal facets featured with facet-dependent physical and chemical properties can exhibit varied electrocatalytic activity toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) attributed to their anisotropy.The highly active exposed crystal facets enable increased mass activity of active sites, lower reaction energy barriers, and enhanced catalytic reaction rates for HER and OER.The formation mechanism and control strategy of the crystal facet, significant contributions as well as challenges and perspectives of facet-engineered catalysts for HER and OER are provided.The electrocatalytic water splitting technology can generate high-purity hydrogen without emitting carbon dioxide, which is in favor of relieving environmental pollution and energy crisis and achieving carbon neutrality. Electrocatalysts can effectively reduce the reaction energy barrier and increase the reaction efficiency. Facet engineering is considered as a promising strategy in controlling the ratio of desired crystal planes on the surface. Owing to the anisotropy, crystal planes with different orientations usually feature facet-dependent physical and chemical properties, leading to differences in the adsorption energies of oxygen or hydrogen intermediates, and thus exhibit varied electrocatalytic activity toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this review, a brief introduction of the basic concepts, fundamental understanding of the reaction mechanisms as well as key evaluating parameters for both HER and OER are provided. The formation mechanisms of the crystal facets are comprehensively overviewed aiming to give scientific theory guides to realize dominant crystal planes. Subsequently, three strategies of selective capping agent, selective etching agent, and coordination modulation to tune crystal planes are comprehensively summarized. Then, we present an overview of significant contributions of facet-engineered catalysts toward HER, OER, and overall water splitting. In particular, we highlight that density functional theory calculations play an indispensable role in unveiling the structure–activity correlation between the crystal plane and catalytic activity. Finally, the remaining challenges in facet-engineered catalysts for HER and OER are provided and future prospects for designing advanced facet-engineered electrocatalysts are discussed.

Crystallographic control of crystals as catalysts with precise geometrical and chemical features is significantly important to develop sustainable chemistry, yet highly challenging. Encouraged by first principles calculations, precise structure control of ionic crystals could be realized by introducing an interfacial electrostatic field. Herein, we report an efficient in situ dipole-sourced electrostatic field modulation strategy using polarized ferroelectret, for crystal facet engineering toward challenging catalysis reactions, which avoids undesired faradic reactions or insufficient field strength by conventional external electric field. Resultantly, a distinct structure evolution from tetrahedron to polyhedron with different dominated facets of Ag₃PO₄ model catalyst was obtained by tuning the polarization level, and similar oriented growth was also realized by ZnO system. Theoretical calculations and simulation reveal that the generated electrostatic field can effectively guide the migration and anchoring of Ag⁺ precursors and free Ag₃PO₄ nuclei, achieving oriented crystal growth by thermodynamic and kinetic balance. The faceted Ag₃PO₄ catalyst exhibits high performance in photocatalytic water oxidation and nitrogen fixation for valuable chemicals production, validating the effectiveness and potential of this crystal regulation strategy. Such an electrically tunable growth concept by electrostatic field provides new synthetic insights and great opportunity to effectively tailor the crystal structures for facet-dependent catalysis.

Cu2O nanoparticles (NPs) enclosed with different crystal facets, namely, c-Cu2O NPs with {100} facets, o-Cu2O NPs with {111} facets, and t-Cu2O NPs with both {111} and {100} facets, are prepared and their electrocatalytic properties for the reduction of CO2 to C2H4 are evaluated. It is shown that the selectivity and activity of the C2H4 production depend strongly on the crystal facets exposed in Cu2O NPs. The selectivities for the C2H4 production increases in the order, c-Cu2O < o-Cu2O < t-Cu2O, (with FEC2H4 = 38%, 45%, and 59%, respectively). This study suggests that Cu2O NPs are more likely responsible for the selectivity and activity for the C2H4 production than the metallic Cu NPs produced on the surface of Cu2O NPs. This work provides a new route for enhancing the selectivity of the electrocatalytic CO2 reduction by crystal facet engineering.Cu2O nanoparticles (NPs) enclosed with different crystal facets, namely, c-Cu2O NPs with {100} facets, o-Cu2O NPs with {111} facets, and t-Cu2O NPs with both {111} and {100} facets, are prepared and their electrocatalytic properties for the reduction of CO2 to C2H4 are evaluated. It is shown that the selectivity and activity of the C2H4 production depend strongly on the crystal facets exposed in Cu2O NPs. The selectivities for the C2H4 production increases in the order, c-Cu2O < o-Cu2O < t-Cu2O, (with FEC2H4 = 38%, 45%, and 59%, respectively). This study suggests that Cu2O NPs are more likely responsible for the selectivity and activity for the C2H4 production than the metallic Cu NPs produced on the surface of Cu2O NPs. This work provides a new route for enhancing the selectivity of the electrocatalytic CO2 reduction by crystal facet engineering.

High-performance ethanol sensors with low power consumption show critical applications in environmental monitoring, personal health diagnosis, industry and traffic safety. Herein, MoO3/Nb2C MXene heterojunction gas-sensing materials were constructed via a one-step hydrothermal method for MoO3 nanotube synthesis. The dominant facets of MoO3 were shifted from the (040) orientation in MoO3 nanotubes to the (110) and (021) orientations in the MoO3/Nb2C MXene composite. Nb2C nanosheets provide a large number of crystallization sites, preventing the growth of MoO3 nanotubes during synthesis, inducing a strategic facet release. The sensing performance shows MoO3/Nb2C MXene composite reduces the operating temperature down to 120 °C. The 15 wt% Nb2C MXene-precursor-mixed MoO3 sensor exhibits an enhanced response of 6.1 toward 100 ppm ethanol, which is higher than that of pristine MoO3 nanotubes at 120 °C, with response and recovery times of 19 s and 72 s, respectively. The sensors show high selectivity toward ethanol over other VOC gases and good long-term stability over 30 days. This work confirms that crystal engineering is an effective method for reducing operating temperature and enhancing gas-sensing performance, and the sensor shows potential application for ethanol sensing.

Water electrolysis represents one of the most environmentally friendly methods for hydrogen production, while its overall efficiency is primarily governed by the electrocatalyst. Nickel sulfides, e.g., Ni3S2, are considered to be highly promising catalysts for the hydrogen evolution reaction (HER) due to their distinctive chemical structure. However, the practical application of Ni3S2-based electrocatalysts is hindered by unsatisfactory high overpotential in the HER and weakened catalytic performance under alkaline conditions. Therefore, in this regard, further research on Ni3S2-based catalysts is being carried out to tackle these challenges. This review provides a comprehensive survey of the latest advancements in Ni3S2-based in improving the HER performance of Ni3S2-based electrocatalysts. The review may offer some inspiration for the rational design and synthesis of novel transition metal-based catalysts with enhanced water electrolysis performance.

HighlightsThe (011) facet has excellent charge transport properties achieving closer alignment of energy levels.By exploiting the (011) facet a device (0.06 cm2) and a module (29 cm2) achieved power conversion efficiencies of 25.24% and 21.12%, respectively.Perovskite crystal facets greatly impact the performance and stability of their corresponding photovoltaic devices. Compared to the (001) facet, the (011) facet yields better photoelectric properties, including higher conductivity and enhanced charge carrier mobility. Thus, achieving (011) facet-exposed films is a promising way to improve device performance. However, the growth of (011) facets is energetically unfavorable in FAPbI3 perovskites due to the influence of methylammonium chloride additive. Here, 1-butyl-4-methylpyridinium chloride ([4MBP]Cl) was used to expose (011) facets. The [4MBP]+ cation selectively decreases the surface energy of the (011) facet enabling the growth of the (011) plane. The [4MBP]+ cation causes the perovskite nuclei to rotate by 45° such that (011) crystal facets stack along the out-of-plane direction. The (011) facet has excellent charge transport properties and can achieve better-matched energy level alignment. In addition, [4MBP]Cl increases the activation energy barrier for ion migration, suppressing decomposition of the perovskite. As a result, a small-size device (0.06 cm2) and a module (29.0 cm2) based on exposure of the (011) facet achieved power conversion efficiencies of 25.24% and 21.12%, respectively.

Rational construction of the facet engineering over metal-organic frameworks is of significant interest for enhancing photocatalytic performance, yet the role of modulator except regulating facet is largely ignored. Herein, facet engineering of NH 2 -MIL125 (aMIL) was achieved through the facile one-pot method by controlling the concentration of acetic acid modulator. The probable domino effects induced with the detectable modulator were extensively investigated, evidencing the multi-position in one mode contained powder X-Ray diffraction (PXRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS), etc. Meanwhile, correlation among the {111} facets engineering, the degree of structural defects, and the performance of photocatalytic hydrogen peroxide (H 2 O 2 ) production was studied in detail, revealing that facet and defect engineering respectively play positive and relatively negative roles in the photocatalytic oxygen reduction reaction (ORR) with a volcano-type trend. aMIL-3 photocatalyst could deliver H 2 O 2 production rate of 925.8 µmol·h −1 ·g −1 (2.03-fold of aMIL) under visible-light irradiation and a quantum yield of 1.08% at 420 nm.

Oxygen evolution reaction (OER) still suffers from the bottleneck in electrocatalytic water splitting. Herein, in virtue of volcano plots drawn by theoretical calculation, the (001) facet was screened as the superb facet of orthorhombic CoSe 2 for OER. Afterwards, CoSe 2 (001) nanosheets were synthesized and the exposure ratio of (001) facet is controllable with thermodynamics methods effectively. The single-facet CoSe 2 (001) delivered an overpotential as low as 240 mV at 10 mA·cm −2 in 1 M KOH, which outperformed the bulk (380 mV) as well as other CoSe 2 -base OER catalysts reported before. Especially, a shorter Co-Co path was observed in CoSe 2 (001) by X-ray absorption spectroscopy. Further density functional theory (DFT) studies revealed that the reversible compression on the shorter Co-Co path could regulate the electronic structure of active sites during the OER process, and thus the energy barrier of the rate-determining step was reduced by 0.15 eV. This work could inspire more insights on the modification of electronic structure for OER electrocatalysts.

Crystallographic facets and phase structures play a decisive role in determining interfacial electrochemical reactions by dictating surface characteristics. In electrochemical catalysis, conventional polycrystalline catalysts often obscure intrinsic structure–activity relationships due to their structural heterogeneity. Single‐crystal and facet‐controlled catalysts therefore serve as well‐defined model platforms for establishing direct correlations between atomic‐scale surface properties and electrochemical performance. This review highlights recent advances in facet‐ and phase‐engineered electrocatalysts, with a primary focus on transition‐metal phosphides (TMPs). Starting from the fundamental facet‐dependent phenomena revealed by noble metal single crystals, we bridge these insights to TMPs, clarifying how facets and phase structures modulate electronic and adsorption properties along with outlining the synthetic principles governing their structural evolution. Emerging synthetic platforms, including liquid metal–assisted synthesis, are reviewed as enabling routes to single‐crystalline catalysts with controlled facets and phases. Finally, we address key challenges in translating fundamental model surface insights into scalable electrode architectures and provide perspectives on future research directions. Facet and phase engineering enables selective electrocatalysis in single‐crystalline transition‐metal phosphides by controlling surface termination, phase identity, and intermediate binding. This review connects noble metal benchmarks, phosphide phase evolution, synthetic growth principles, and electrode translation to guide rational catalyst design for H2O2 synthesis, CO2 reduction, and nitrate conversion.

Direct methanol fuel cells have emerged as highly promising energy conversion devices in the past few decades. However, some challenges, such as carbon monoxide (CO) poisoning and unsatisfactory long-term stability, remain for platinum (Pt) as a methanol oxidation reaction (MOR) catalyst. This review covers recent advances in Pt alloy MOR catalysts and provides some insights. This review presents MOR catalytic mechanisms based on CO or non-CO pathways. Typical dimension-based designs of MOR catalysts, such as anisotropic nanowires, metallene, nanoframes, and corresponding rationales for performance enhancements, are introduced. More importantly, some key tuning strategies are elaborated, including intermetallic compound synthesis, interface engineering, and surface facet engineering. High-entropy alloys as an intriguing class of MOR catalysts with favorable prospects are also discussed. Finally, future directions and opportunities are outlined.