Heterogeneous electrochemical phenomena, such as (photo)electrochemical water splitting to generate hydrogen using semiconductors and/or electrocatalysts, are driven by the accumulated charge carriers and thus the interfacial electrochemical potential gradients that promote charge transfer. However, measurements of the “surface” electrochemical potential during operation are not generally possible using conventional electrochemical techniques, which measure/control the potential of a conducting electrode substrate. Here we show that the nanoscale conducting tip of an atomic force microscope cantilever can sense the surface electrochemical potential of electrocatalysts in operando. To demonstrate utility, we measure the potential-dependent and thickness-dependent electronic properties of cobalt (oxy)hydroxide phosphate (CoPi). We then show that CoPi, when deposited on illuminated haematite (α-Fe₂O₃) photoelectrodes, acts as both a hole collector and an oxygen evolution catalyst. We demonstrate the versatility of the technique by comparing surface potentials of CoPi-decorated planar and mesoporous haematite and discuss viability for broader application in the study of electrochemical phenomena.

异质电化学现象，例如使用半导体和/或电催化剂分解（光）电化学水以产生氢的化学现象，是由积累的电荷载流子驱动的，并由此促进电荷转移的界面电化学势梯度驱动。然而，使用常规的电化学技术通常不可能测量操作期间的“表面”电化学电势，所述常规的电化学技术测量/控制导电电极基底的电势。在这里，我们表明原子力显微镜悬臂的纳米级导电尖端可以在操作中感应电催化剂的表面电化学势。为了证明其实用性，我们测量了磷酸钴（氧）氢氧化物（CoPi）的电势依赖性和厚度依赖性。₂ O ₃）光电电极既充当空穴收集器又充当析氧催化剂。我们通过比较CoPi装饰的平面和介孔赤铁矿的表面电势来证明该技术的多功能性，并讨论了在电化学现象研究中更广泛应用的可行性。