The use of fast surface redox storage (pseudocapacitive) mechanisms can enable devices that store much more energy than electrical double-layer capacitors (EDLCs) and, unlike batteries, can do so quite rapidly. Yet, few pseudocapacitive transition metal oxides can provide a high power capability due to their low intrinsic electronic and ionic conductivity. Here we demonstrate that two-dimensional transition metal carbides (MXenes) can operate at rates exceeding those of conventional EDLCs, but still provide higher volumetric and areal capacitance than carbon, electrically conducting polymers or transition metal oxides. We applied two distinct designs for MXene electrode architectures with improved ion accessibility to redox-active sites. A macroporous Ti₃C₂T_x MXene film delivered up to 210 F g⁻¹ at scan rates of 10 V s⁻¹, surpassing the best carbon supercapacitors known. In contrast, we show that MXene hydrogels are able to deliver volumetric capacitance of ∼1,500 F cm⁻³ reaching the previously unmatched volumetric performance of RuO₂.

快速表面氧化还原存储（伪电容）机制的使用可以使设备存储的能量比双电层电容器（EDLC）多得多，并且与电池不同，它可以非常迅速地进行存储。然而，由于伪电子过渡金属氧化物的固有电子和离子导电率低，因此很少能提供高功率能力。在这里，我们证明了二维过渡金属碳化物（MXenes）可以超过常规EDLC的速率运行，但仍比碳，导电聚合物或过渡金属氧化物提供更高的体积和面积电容。我们为MXene电极架构应用了两种不同的设计，改善了离子对氧化还原活性位点的可及性。大孔Ti ₃ C ₂ T _xMXene薄膜以10 V s ^-1的扫描速率提供高达210 F g ^-1的薄膜，超过了已知的最佳碳超级电容器。相反，我们表明MXene水凝胶能够提供约1,500 F cm ^-3的体积电容，从而 达到RuO ₂以前无法比拟的体积性能。