Controlling the synthesis of metal nanostructures is
one approach
for catalyst engineering and performance optimization in electrocatalysis.
As an emerging class of unconventional electrocatalysts, two-dimensional
(2D) metallene electrocatalysts with ultrathin sheet-like morphology
have gained ever-growing attention and exhibited superior performance
in electrocatalysis owing to their distinctive properties originating
from structural anisotropy, rich surface chemistry, and efficient
mass diffusion capability. Many significant advances in synthetic
methods and electrocatalytic applications for 2D metallenes have been
obtained in recent years. Therefore, an in-depth review summarizing
the progress in developing 2D metallenes for electrochemical applications
is highly needed. Unlike most reported reviews on the 2D metallenes,
this review starts by introducing the preparation of 2D metallenes
based on the classification of the metals (e.g., noble metals, and
non-noble metals) instead of synthetic methods. Some typical strategies
for preparing each kind of metal are enumerated in detail. Then, the
utilization of 2D metallenes in electrocatalytic applications, especially
in the electrocatalytic conversion reactions, including the hydrogen
evolution reaction, oxygen evolution reaction, oxygen reduction reaction,
fuel oxidation reaction, CO2 reduction reaction, and N2 reduction reaction, are comprehensively discussed. Finally,
current challenges and opportunities for future research on metallenes
in electrochemical energy conversion are proposed.